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

SHALLOW LEVEL LOW-SULPHIDATION TYPE EPITHERMAL SYSTEMS IN THE REGEC CALDERA, CENTRAL TOKAJ MTS., NE-HUNGARY

Pages: 217 - 227

Authors: BERNADETT BAJNOCZI, FERENC MOLNAR, KATSUHIKO MAEDA, EIJI IZAWA

Abstract: Detailed investigation of the Regec caldera in the Central Tokaj Mts. revealed several types of hydrothermal centers of low-sulphidation type formed at different paleolevels. At the paleosurface, a hydrothermal eruption breccia and layered siliceous deposit of opal-C and -CT material with cinnabar and anomalous enrichments of Hg and Sb were formed from a hot spring. Silicified tuff horizons with alunite-kaolinite alteration indicate steam-heated zones. This type of alteration was formed in the near surface zone, probably above the paleowater table. Stable isotope data for large-sized alunite crystals in brecciated tuff may also indicate a magmatic steam origin. In the deeper zone, around 90–140 m minimal paleodepth, adularia-sericite alteration with quartz veining in andesite formed with anomalous Sb, As and Ba concentrations. Two stages of K-feldspar formation can be recognized: 1. metasomatic K-feldspar, replacing plagioclase phenocrysts, and 2. late adularia in quartz-pyrite-veinlets. Intensive brecciation and adularia formation suggest a pressure drop and boiling of the mineralizing fluids. Late stage quartz crystals show frequent homogenization temperatures between 170 and 190 °C and a maximum salinity of 3 wt. % NaCl equiv. Stable isotope data for quartz crystals suggest that the dominant mineralizing fluid was meteoric water that underwent exchange reaction with the host rock and/or mixed with magmatic water.

Keywords: Tokaj Mountains, epithermal systems, low-sulphidation type, fluid inclusions, stable isotopes

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