Karbonatova hydrotermalni zilna mineralizace v granitoidnich horninach stredoceskeho plutonu na lozisku zlata Mokrsko-zapad

The Mokrsko-West underground research laboratory (50 km S of Prague) is a part of the Čelina-Mokrsko gold deposit, which represents the largest gold accumulation in the Bohemian Massif. At present, the Josef Gallery - the Josef UEF - an underground educational facility at the Mokrsko-West deposit enables the research of the interactions between the geological environment and construction materials, and tests on the long-term stability of materials.
The older type of hydrothermal veins is formed by steeply dipping Au-bearing quartz veins of E-W strike. Au (> 850/1000), and sparse Au₂Bi occur in arsenopyrite. Au-bearing quartz veins were formed at the temperature up to 400 °C at the low-salinity H₂O-CO₂±CH₄ fluids (Boiron et al. 2001).
In this contribution, we focused on the later type of hydrothermal veins represented by steep calcite veins of N-S, and E-W strike, and subhorizontal calcite veins of NW-SE strike, dipping to NW.
Only fluids of the H₂O-type were found in inclusions in the calcite. Temperatures of homogenization yielded valuable data in the range from 60 to 160 °C, and the salinity of the solution was found to be from 0.2 to 9.3 mass % NaCl equiv.
The fluids depositing the calcite had δ¹³C values ranging from -7.9 to -14.65 ‰ PDB, and δ¹⁸O values between -0.87 and 6.45 ‰ SMOW. It means that the waters of deeper circulation in metamorphic rocks and meteoric waters of shallow circulation can be considered to be the mature fluids.
The values of Sr content higher than 100 ppm, together with REE pattern indicate the hydrothermal origin of calcites. On the basis of structural position of the veins, and the fission track analyses in apatites, the calcite veins are believed to be Post-Variscan.
AFT analysis was used for the age measurement and time-temperature modeling. All samples revealed very similar time-temperature paths. The rocks were uplifted from zone of total annealing (≤ 120 °C) in 180 Ma, then the temperature slowly decreased from 120 °C to 80 °C, subsequently stagnated, and finally (10 Ma ago) quickly decreased to the present temperature.

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