Shallow level low-sulphidation type epithermal systems in the Regec caldera, Central
Tokaj Mts., NE-hungary
Bajnoczi B, Molnar F, Maeda K, Izawa E
GEOLOGICA CARPATHICA
51 (4): 217-227 AUG 2000
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, adulariasericite 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 Kfeldspar, 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 degrees 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.