International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Triassic fluid mobilization and epigenetic lead-zinc sulphide mineralization in the Transdanubian Shear Zone (Pannonian Basin, Hungary)

Pages: 177 - 194

Authors: ZSOLT BENKÓ, FERENC MOLNÁR, MARC LESPINASSE, KJELL BILLSTRÖM, ZOLTÁN PÉCSKAY, TIBOR NÉMETH

Abstract: A combined fluid inclusion, fluid inclusion plane, lead isotope and K/Ar radiometric age dating work has been carried out on two lead-zinc mineralizations situated along the Periadriatic-Balaton Lineament in the central part of the Pannonian Basin, in order to reveal their age and genetics as well as temporal-spatial relationships to other lead-zinc- fluorite mineralization in the Alp-Carpathian region. According to fluid inclusion studies, the formation of the quartz- fluorite-galena-sphalerite veins in the Velence Mts is the result of mixing of low (0—12 NaCl equiv. wt. %) and high salinity (10—26 CaCl2 equiv. wt. %) brines. Well-crystallized (R3-type) illite associated with the mineralized hydrother- mal veins indicates that the maximum temperature of the hydrothermal fluids could have been around 250 °C. K/Ar radiometric ages of illite, separated from the hydrothermal veins provided ages of 209—232 Ma, supporting the Mid- to Late-Triassic age of the hydrothermal fluid flow. Fluid inclusion plane studies have revealed that hydrothermal circulation was regional in the granite, but more intensive around the mineralized zones. Lead isotope signatures of hydrothermal veins in the Velence Mts (206Pb/204Pb = 18.278—18.363, 207Pb/204Pb = 15.622—15.690 and 208Pb/204Pb = 38.439—38.587) and in Szabadbattyán (206Pb/204Pb = 18.286—18.348, 207Pb/204Pb = 15.667—15.736 and 208Pb/204Pb = 38.552—38.781) form a tight cluster indicating similar, upper crustal source of the lead in the two mineralizations. The nature of mineralizing fluids, age of the fluid flow, as well as lead isotopic signatures of ore minerals point towards a genetic link between epigenetic carbonate-hosted stratiform-stratabound Alpine-type lead-zinc-fluorite deposits in the Southern and Eastern Alps and the studied deposits in the Velence Mts and at Szabadbattyán. In spite of the differences in host rocks and the depth of the ore precipitation, it is suggested that the studied deposits along the Periadriatic-Balaton Lineament in the Pannonian Basin and in the Alps belong to the same regional scale fluid flow system, which developed during the advanced stage of the opening of the Neo-Tethys Ocean. The common origin and ore formation process is more evident considering results of large-scale palinspastic reconstructions. These suggest, that the studied deposits in the central part of the Pannonian Basin were located in a zone between the Eastern and Southern Alps until the Early Paleogene and were emplaced to their current location due to northeastward escape of large crustal blocks from the Alpine collision zone.

Keywords: Triassic, Velence Mts, Szabadbattyán, Periadriatic-Balaton Lineament System, lead isotopes, fluid inclu- sions, Alpine-type epigenetic lead-zinc mineralization

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