Kamen BogdanovAssociate Professor of MineralogySOFIA UNIVERSITY “St. Kl. Ohridski”Faculty of Geology and Geography 15 Tsar Osvoboditel Bd. 1000 Sofia, Bulgaria E-mail: kamen@gea.uni-sofia.bg |
Ivan Pojarevski G.D.Gem President of BULGARIA GEMS Ltd 128 Tsar Boris Bd. Bl16, entr. B 1618 Sofia, BULGARIA .E-mail: bg.gems@datacom.bg |
The Republic of Bulgaria covers territory of 110 994 km2 and is situated in the SE part of the Balkan peninsula, which lies entirely within the Alpine folded belt. The territory of Bulgaria covers part of the Moesian platform (to the north) and almost the entire Rhodope massive (to the south) , as well as the northern part of the Alpine folded belt known as Balkanides.
According to Bogdanov (1980) and Ivanov,(1988, 2001) the major tectonic and metallogenic units important for different mineral deposits in Bulgaria (Fig.1) are:
1.Moesian platform; 2.Balkanides; 3.Srednogorie zone; 4.Rhodope massif
The most important economically and from mineralogical point of view mineral deposits and unique mineral species and samples in Bulgaria are located in the Srednogorie zone and the Rhodope massif.
The Moesian Platform covers the Northern part of Bulgaria and has a Precambrian and Paleozoic basement and Mezosoic cover of shallow marine sediments. The sedimentary deposits of gypsum (Koshava), fireclays(Pleven), kaolinite ( Razgrad), salt (Provadia) and manganese(Obrochishte) are characteristic for the Moesian Platform.
The Balkanides are segment of the northern branch of the Alpine folded beltin Southeast Europe that includes (Ivanov,1988, 2001) External,Intermediate and Internal Balkanides.
The External Balkanides are situated immediately to the South of the Moesian Platform and include the Balkan Mountains(Stara Planina Mountain).
The Srednogorie Zone (Fig.1) is part of the Intermediate Balkanides and has been developed as Upper Cretaceous island arc system, strongly affected by subduction related magmatism. The porphyry-copper (Assarel, Medet, Tsar Assen, Elatsite) and epithermal gold–copper deposits (Chelopech, Krassen,Radka, Elshitsa) are most important sources for Au, Ag, Se,Te,Ga, Ge, In and some rare minerals such as kostovite, germanite, roquesite, etc.
The Internal Balkanides with: a) Sakar – Strandga zone: composed of metamorphosed Triassic and Jurassic sediments.; and b) Kraishte zone.
The Rhodope Massif (Fig. 1) is built up of regional metamorphic rocks, such as granitised gneisses mica gneisses, amphibolites, schists and marbles(Bogdanov 1960, Vergilov 1963), intruded by large bodies of post metamorphic granitoides, as a result of Upper Cretaceous to Tertiary extension (Ivanov,1988, 2000; Ivanov et al., 2000;Burg et al.,1989, 1995,1998).
The most important types of ore deposits in Bulgaria are:Copper deposits (Porphyry-copper, Epithermal Cu-Au-sulphide deposits,Cu-vein type deposits, Scarn type deposits); Gold deposits(Mesothermal vein type and Epithermal (LS) and (HS) type); Lead-zinc-silver deposits (Mesothermal veins and replacement type); Iron and Manganese deposits;Pegmatite deposits.
The distribution of the main types of mineral deposits in the different tectonic and metallogenic units in Bulgaria is specific. Base-metal and gold deposits occur in the Balkan zone (External Balkanides).
Copper, gold and iron deposits are characteristic for the Srednogorie zone, while the lead-zinc-silver deposits and fluorite deposits are most typical for the Rhodope Massif (Figs.1, 2). The pegmatite deposits are characteristic for the Srednogorie zone, the External Balkanides and the Rhodope massif. Salt, gypsum, manganese and fire clay deposits are important for the Moesian platform, while zeolite (clinoptilolite deposit Beli Plast) deposits occur in the Eastern Rhodopes.
The porphyry - copper deposits (Medet, Assarel, Tsar Assen and Elatsite) from the Srednogorie and Balkan zones of Bulgaria are connected to subvolcanic granodiorite and quartz-diorite porphyryte intrusions, while the volcanic hosted epithermal deposits Elshitsa, Radka, Krassen and Chelopech are related to andesite - dacite magmatic activity that took place about 65 - 94 m. y. ago (Bogdanov,1984,1986;Lilov, Chipchakova,1999).
The base-metal (Pb-Zn-Cu-Ag)and epithermal low - and high sulphidation gold deposits in the eastern part of the Rhodope massif are results of the Late Paleogene collisional stage of the development of the tectono-magmatic and hydrothermal processes during the longlasting subduction proccesses of the African and the Eurasian tectonic microplates as a final stage of the Tethys closure(De Boorder et al.,1998). Madjarovo, Spahievo, Zvezdel and Lozen base-metal Au-Ag deposits (Fig. 1) were formed during Miocene hydrothermal activity in the eastern part of the Rhodope massif. The main ore veins and lenses of galena-sphalerite-chalcopyrite are hosted by Tertiary volcano - plutonic and terrigeneous sequences. The different geodynamic scenarios and the ore-remobilisation processes during the Phanerozoic metallogeny in Bulgaria led to significant, but also different behavior of the mineral assemblages that are important Au-Ag-carriers and their isotope and fluid evolution.
The Pb-Zn(-Cu-Ag-Au) hydrothermal vein deposits in the Madan extensional core complex in the Bulgarian Rhodope Mountains (Bogdanov,1960, Z. Ivanov, 1998, 2000.; Kolkovski et al., 1996; 2000) are the most important source for Pb-Zn and Ag in Bulgaria. More than 30 Pb-Zn-Ag deposits (Fig. 2) represented by mesothermal veins and johannsenite-rhodonite scarn type ore bodies,are emlaced along six subparallel NW striking faults in the Madan ore field. The Pb-U age of the deposits is 30-40 m.y.(Bogdanov,1974). The ore veins are 0.5-1.9 km long and up to 10m wide. They consist of quartz, pyrite, galena, sphalerite, tennantite, Mn carbonates, barite that have been deposited at the temperature range 350-105 oC as a result of fluid boiling,interaction and neutralization in marble horizons (G.Palas, Ribnitsa, Strashimir,Mogilata ,Osikovo, Krushev Dol mines, etc.).
Minerals and deposits in the Madan ore field
The lead – zinc deposits of MADAN ORE FIELD (Fig.2) were operated by the Turks in the Middle Ages . Greek coins from Tassos island dating from 14th century AD, have been foud in the ancient galleries, as well as name of the “Madan” field, which in Turkish means “ore” originates from that time (Bogdanov,1980). During 1947-1995 the Madan ore field produced 94 887 t. ore with 2 412 459 t Pb and 1 991 586 t Zn.
The Madan ore field is built up mainly of the highly crystalline rocks of the lower (Ar) and upper (Pt) metamorphic units which form the Madan dome structure (B. Bogdanov, 1960, Ivanov,1988, 2000). The lead – zinc deposits of the Madan ore field are represented by: 1. Ore veins of quartz – carbonate – sulphide composition, and 2. Metasomatic scarn deposits of johannsenite – rhodonite, or quartz – sulphide composition.
The principal part of the lead – zinc ores in the ore field is concentrated in ore veins emplaced along five subparallel faults striking NW and cutting rhyolitic dykes and Oligocene conglomerates and breccias. The host rocks alternations are of quartz – sericite – chlorite type. The main minerals in the ore veins are: galena and sphalerite, which are almost accompanied by pyrite, chalcopyrite, arsenopyrite, alabandite, tetrahedrite, etc.. Native silver and silver bearing minerals, Ag-sulphosalts, gold and electrum are also found. Among the vein minerals quartz, rodochrosite, mangancalcite, and calcite are of widest occurrence.
Scarn and massive sulphide metasomatic deposits (Fig. 2) in the Madan ore field are formed at the intersections between the marble beds and the ore veins. The scarn deposits comprise radial aggregates of johannesite bustamite and rhodonite. They are formed at the very beginning of the hydrothermal infiltration scarns. The studies of the filling temperatures of the fluid inclusions in quartz, sphalerite, carbonites and barite show that the sxcarns were formed at over 400 degrees C, the quartz – pyrite ore at 320-350 degrees C, the quartz – sphalerite – galena ore at 210 – 300 degrees C, carbonates at 90 – 180 o C and baryte at 50 o C. (Bogdanov,1960; Kolkovski et al,1980; Petrov, 2000).
The mineral diversity of Bulgaria
In the beginning of 2001 the knowm minerals in Bulgaria include 1054 mineral names. In Bulgaria have been discovered new and rare minerals such as:
Ardaite Pb17Sb15S33Cl9 Balkanite Cu9Ag5HgS8 Bonchevite PbBi4S7 Germanocolusite Cu26V2(Ge,As)6S36 HemusiteCu6SnMoS8 Kostovite AuCuTe4 Orpheite H6Pb8Al20[PO4]12(SO4)5 (OH)40 11H2O Stibiocolusite Cu26V2(Sb,Sn,As)6S36 Strashimirite Cu4(AsO4)2(OH)2.2.5H2O; Vasilite (PdCu)16(S,Te)7 Kiddcreekite Cu6.01Sn1.0W1.0S7.98 .
The pyrite and galena and sphalerite and chalcopyrite are the most widespread minerals in the Cu-Au and Pb-Zn-Ag deposits in the Srednogorie and in the Madan areas in Bulgaria. All the four sulphide minerals display a great diversity of crystal habits due to the local variations of the crystallization environment in the different genetical type of mineral deposit.
Pyrite is the most widespread mineral in the different ore deposits types in Bulgaria. The most common crystal forms and habits of pyrite in the mineral deposits from the Srednogorie zone and the Rhodopes in Bulgaria are: {100}, {110}, {111} and {210}. The {100} and {210} form are most typical (Fig.13,14) for the late stages of the mineral deposition and temperatures of formation 270-150 oC. In some cases(Lozen ore field, Eastern Rhodopes) the {210} habit type is characteristic for the zones of the mineral deposits enriched in Au. The {111} habit is regarded as more high temperature type . The {321} diploidal habit of pyrite is rare, but could be found in the pyrite from the Madan ore field.
Galena is the most characteristic mineral in the Madan ore field in Bulgaria. The most common crystal forms and habits of galena in the mineral deposits from the the Rhodopes in Bulgaria are: {100}, {110}, {111} , {211} and {210}. The {100} and {111} form are most typical for the different mineral assemblages (Fig. 9, 13, 14). Large galena {100} and {111} 20 cm crystals were reported from Madan and still can be found in some mines. The {111} habit type is characteristic for some Bi rich zones of the mineral deposits, while the {100} habit is more common in Ag rich zones. Epitaxy phenomena , etch figures and galena twins by spinel law are frequently observed.
The sphalerite displays most of the basic forms (Fig.15) in the mineral deposits from the the Rhodopes : {111}, {1-11}, {11-1}, {110}, {1-1-1}, {011} , {211} and {210}. Large green {111} 7 cm crystals were reported last wears from Madan are still con be found in some mines. The {111} habit type is characteristic for some Fe rich marmatite varieties. Sphalerite twins by spinel law are frequently observed.
The chalcopyrite displays most of the basic forms in the mineral deposits from the the Rhodopes : {112}, , {001}, {110}, {101}, {011} , {332} and {012}. Chalcopyrite whiskers from Madan have also been reported.
The great diversity of the mineral habits could be a result of the specific local variations of the crystallizational environment , as well as to the changes of the P/T conditions of mineral formations.
