The Krasna Hora, Mileov, and PA (TM) iovy Sb-Au ore deposits, Bohemian Massif: mineralogy, fluid inclusions, and stable isotope constraints on the deposit formation
Abstract
The Krasna Hora-Mileov and PA (TM) iovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks.
Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krasna Hora-Mileov) or are associated with local strike-slip faults (PA (TM) iovy).
Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at similar to 250 to similar to 130 A degrees C and gold at similar to 200 to similar to 130 A degrees C from low-salinity aqueous fluids.
The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 A degrees C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature (similar to 250 MPa, similar to 400 A degrees C).
The estimated oxygen isotope composition of the ore-bearing fluid (4 +/- 1aEuro degrees SMOW; based on post-ore calcite) suggests its metamorphic or mixed magmatic-metamorphic origin and excludes the involvement of meteoric water. Rapid cooling of warm hydrothermal fluids reacting with "cold" host rock was probably the most important factor in the formation of both stibnite and gold.