Kónya Péter (szerk.): A Bakony-Balaton-felvidék vulkáni terület ásványai - TQS Monographs 1. (Miskolc - Budapest, 2015)
Kónya P. - Bozsó G. - Bartha A.: A Bakony-Balaton-felvidék vulkáni terület üregkitöltő kalcitja
Kónya P. (szerk.) (2015): A Bakony-Balaton-felvidék vulkáni terület ásványai. TQS Monographs 1. Miskolc-Budapest: Herman Ottó Múzeum és Magyar Földtani és Geofizikai Intézet, pp. 171-180. A Bakony-Balaton-felvidék vulkáni terület üregkitöltő kalcitja Cavity filling calcitefrom the Bakony-Balaton Highland Volcanic Field, Hungary Kónya Péter1*, Bozsó Gábor2, Bartha András3 * 'Magyar Földtani és Geofizikai Intézet, 1143 Budapest, Stefánia út 14. 2Szegedi Tudományegyetem, Ásványtani, Geokémiai és Kőzettani Tanszék, 6722 Szeged, Egyetem u. 2-6. 3Cemkut Kft, 1034 Budapest, Bécsi út 122-124. 'e-mail: konya.peter@mfgi.hu Abstract Calcite is the most frequent carbonate mineral in the cavities of the basalt of the Bakony-Balaton Highland Volcanic Field (BBHVF). Calcite was the first investigated at the beginning of the 20th century from Hajagos and Guides hills, and observed two_generations which were as follows: Generation I: yellow rhombohedral crystals with the forms {0221}, {0552} and {0331}; Generation П: light brown, white or colourless rhombohedra with the forms {0111}, {0221} and {0331}, and hemispheric aggregates. Calcite was studied by stereomicroscope, stable isotope investigations and chemical analyses, and three generations were recognised as related to zeolites (primarily phillipsite and partially natrolite). Generation I. Colourless, white or light yellow rhombohedra and gunspar crystals in close association with phillipsite. Group I/a: white, colourless, rarely light yellow rhombohedra {0111}, 3-4 mm in length, and white to yellow {0221} and {0772} rhombohedra, 1 cm in length. Group I/b: colourless or light yellow hemispheres consisting of {1011} and {0221} rhombohedra. Group I/c: combination of rhombohedron and prism faces. Group I/d: colourless, elongated or stubby gunspar crystals. Group I/e: colourless, rarely white rhombohedron {1011}, 2 mm in length. Generation II. Its crystallization follows zeolites (phillipsite and natrolite group) and calcite-I. Group Il/a: white, rarely light yellow, elongated or stubby scalenohedral crystals, 5-10 mm in length. Group Il/b: elongated, steep scalenohedral calcite, 2-3 cm in length in basalt breccia. Group II/c: colourless, rarely white {1011} rhombohedron, 2 mm in length. Generation I/A: calcite is always associated with the miarolitic minerals. Phillipsite and natrolite group minerals do not occurred with calcite-I/A. Group I/A/a: colourless, white or light yellow {0112} and {1011} rhombohedra, or yellow yellowish brown {0221} rhombohedra. Group I/A/b: white, massive, concentrica! calcite hemisphere on miarolitic minerals. Group I/A/c: colourless, rarely white {1011} rhombohedron, 2 mm in length on hemispheres. Twelve samples were studied by pX-ray Fluorescent method. According to the pXRF results most calcites are pure CaC03. ICP results supported that Mg2+ entered the lattice of the white or colourless calcite, and Fe entered the yellow calcite. Stable isotope studies were made on 12 calcite specimens. The calcite of the BBHVF can be compartmentalized in three groups: Group 1: these calcite samples have the highest d13C values (-2.66 < 8I3C <-6.11%c), and the lowest 8180 values (17.04 < 8180 < 21.48%c). Most cavity filling calcites belong to this group. Group 2: the d13C and 8lsO values vary in a very wide range from -5.50 to -9.90%o, and 22.64 to 25.73%c, respectively. Crystallisation of calcite-II follows zeolites (phillipsite and natrolite group). Group 3: the 813C and 5lsO values vary in a very narrow range from -11.73 to -13.39%c, and 22.27 to 22.59%c, respectively. Calcite is associated with the miarolitic minerals and its status with the main zeolite paragenesis is doubtful. Carbonate component of the BBHVF calcite indicates igneous origin. Positive correlation between MgO and 813C in Generation I—II does not support to rainwater inflow. The generations of calcite were developed by cooling of the system and low to great outgassing. Development of Generation I/A caused by intensive cooling and outgassing parallel to Generation I—II. Stable isotope data show that assuming ~ 100 °C initial crystallization temperature the cooling of the system is characterised by a 70 °C drop in temperature. (Calculations were made with the equation S18Ocald,e-818Of]ulde = 2.78*(Ю6/Т2)-2.89). Összefoglalás A Bakony-Balaton-felvidék vulkáni terület (BBVT) bazaltjainak leggyakoribb üregkitöltő karbonátásványa a kalcit, amelyet részletesen a múlt század első felében Mauritz Béla vizsgált. Kutatásai során kiderült, hogy a kalcit több, de legalább két generációban jelenik meg. A kalcit-I^generációba a nagy mennyiségben megjelenő, maximálisan 2 cm-es, tiszta, átlátszó, sárga romboéderes {0221}, {0552} és {0331} kristályok, míg a kalcit-II-be a világosbarnás {0221} és {0331}, illetve fehéres és színtelen {OlTl} romboéderek, valamint a belőlük összenőtt félgömbök tartoznak, mely utóbbiak zeolitokra települnek.
