Hîrtopanu, Paulina

English

Hîrtopanu Paulina

Scott P. W.

Andersen J. C.

Fairhurst R. J.

Chukanov N. V.

Jakab Gy.

Petrescu L.

University of Szeged

Acta Mineralogica-Petrographica, Abstract Series, Szeged, Vol. 7, 2012 55 Joint 5th Mineral Sciences in the Carpathians Conference and 3rd Central-European Mineralogical Conference 20–21 April, 2012, University of Miskolc, Miskolc, Hungary BARIUM MINERALIZATION WITHIN THE TULGHEŞ GROUP, EAST CARPATHIANS, ROMANIA  HIRTOPANU, P.1*, SCOTT, P.W.2, ANDERSEN, J.C.2, FAIRHURST, R.J.2, CHUKANOV, N.V.3, JAKAB, Gy.4 & PETRESCU, L.1 1 University of Bucharest, Romania; 2 University of Exeter, Camborne School of Mine, UK; 3 Institute of Problems of Chemical Physics, Russia; 4 I.G. Mineral, Gheorgheni, Romania; * E-mail: paulinahirtopanu@hotmail.com  A Ba mineralization, less known than the Mn and sulphide ones, also is situated in the Cambrian Tulgheş Group (TG) extending over more than 200 km. The Mn belt is situated at the bottom and the sulphide belt on the top of TG. The Ba mineralization is present in the whole TG together with both Mn and sulphide belts. It has a large development of about 10 km at the crossing of two belts Holdita-Paraul and Caselor-Brosteni-Borca, with the same orientation (NW-SE), like the Mn and sulphide ores. The mineralogy of TG is simple and uniform being made up generally of five major minerals in variable proportions: quartz, muscovite albite, chlorite, Ca-Mg-Fe-carbonates (± graphite ± titanite ± rutile ± stilpnome-lane ± ilmenite ± magnetite ± pyrite). Its huge thickness is due to its developmental history in a narrow deep, active subduction zone. The rocks of TG are metamor-phosed under greenschist facies and display a pro-nounced schistosity, having some similarities with that of burial metamorphism. During metamorphism, the wall rocks were tidily folded and microsheared. VODA & VODA (1980) have described the Holdita-Brosteni syngenetic barite ore deposit, as conformable beds within the metamorphic formation of the black quartz-ites of the TG. The lithostratigraphical sequence with Ba mineralization of about 80–120 m comprises on the bottom, a lens of Mn ore and on the top, a barite lens banded by sulphide ore. The barite ore contains Ba-feldspars (celsian, hyalophane), cymrite, barytocal-cite, benstonite, aragonite, witherite, phlogopite, sericite, diverse carbonates and quartz. Pyrite, and other sulphides, including sphalerite, bornite, galena, chal-copyrite, tetrahedrite-tennantite also occur. Alabandite, sometimes associated with pyrochroite also occurs in the Mn belt, in reduced tephroite parageneses. The Mn belt also contains other Ba minerals, including celsian, hyalophane, barite and cymrite as accessory minerals. This indicates a genetic link between the Ba and Mn mineralization, which is suggested to have formed by the same submarine hydrothermal process on the Cam-brian sea floor. The lenses of Mn-carbonate-silicate ore are closely interbedded with barite ore. This close inter-bedding of barite, Mn and sulphide ores demonstrates their common origin and evolution. Barite is the main barium mineral (more than 70%) of these deposits, having isometric grains of 0.5 mm diameter and more, forming compact, grainy aggregates from several cm to 4 m. In the Holdita deposit, the late barite replaces the earlier Ba-feldspars. The Holdita barite contains: BaO = 65–77%, SO3 = 33–19%, and SrO = 3–4%. There is some isomorphism with celestine. The hydrothermal activity (like springs) began on the Cambrian seafloor, where the Mn ores were deposited and mixed with little barium mineralization in the distal zones.  In the south-ern area, the barium is predominant, where it is mixed with some Mn and sulphide mineralization. The Ba-feldspars occur in crystals ranging from a few mm to 1 cm and even larger, forming thin layers interbedded with other enriched layers of barite, apatite, sulphides (mostly pyrite, but also alabandite, chalcopyrite occur). Celsian is the predominant Ba-feldspar. Hyalophane is very rare. The primary substitution is between BaAl and KSi series (KAlSi3O8–BaAl2Si2O8) seems to be con-tinuous. However exsolutions of hyalophane in celsian in the same grain shows a compositional gap between the two minerals on the BSE images from Holdita de-posit. The celsian contains over 90% BaAl2Si2O8 com-ponent (Cn), whereas hyalophane contains under 30% Cn, consistent with the presence of a substantial compo-sitional gap. The Ba feldspars are replaced by barite and by cymrite plates (HIRTOPANU et al., 2008). The relics of celsian in cymrite may have escaped the reac-tion because locally PH2O may have been lower than Pfluid, and when PH2O was higher than Pfluid, celsian did not form. The real situation could be more complex kinetically, e.g. the substitution process could be not completed because its speed was too low, or because the activity of H2O decreased. The coexistence and phase relations between celsian and cymrite are of great petrological interest being a natural example of the experimentally established reaction curve, celsian + H2O = cymrite (ESSENE, 1967). The lineally developed Ba, Mn and sulphide mineralization belts evolved in a subduction zone of the Cambrian sea floor, in a narrow active paleotrench area. The hydrothermal submarine activity began with Mn ore with little Ba in the North and more Ba and little Mn in the South. Later, in the upper Cambrian, the sea floor was subducted towards the East and sulphides were deposited at some distance from, and over the Mn ore containing body.  References ESSENE, E.J. (1967): American Mineralogist, 52: 1885–1890. HIRTOPANU, P., ANDERSEN, J.C., CHUKANOV, N. & PETRESCU, L. (2008): Romanian Journal of Mineral Deposits / Romanian Journal of Mineralogy, 83: 58–61. VODA, A. & VODA, D. (1980): Dări de Seamă ale Institutului de Geologie şi Geofizică, 67(2): 233–246. 

Barum mineralization within the Tulgheş group, East Carpathians, Romania

http://acta.bibl.u-szeged.hu/32997/1/mineralogica_as_007_055.pdf

Barum mineralization within the Tulgheş group, East Carpathians, Romania

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