Acta Musei Moraviae

Gold in the quartz veins of the Hláska and Vysoká hora, north field of the Andělská Hora Ore District, Jeseníky Mts., Czech Republic

The lenticular gold-bearing quartz ± carbonate veins at the Vysoká hora Mt. and Hláska Mt. crosscut sericite phyllites of the Vrbno Group. The gold sheets hosted by both quartz and limonitized Mg-rich siderite reach up to 3.5 mm in size and have fineness of ~840–920. Pyrite occurs in two types: early homogeneous and younger porous. Other detected minerals include only accessories: Co-gersdorfite, galena (with ~0.9 wt. % Bi), rutile (sagenite), ilmenite, and albite. Hypergene collomorphic goethite contains grains of monazite and xenotime and rims of hydrohematite. The vugs are filled up by allophanehalloysite, gibbsite, and secondary apatite. The fluid inclusions hosted by quartz and carbonates trapped a heterogeneous mixture of low-salinity (<6 wt. % NaCl eq.) aqueous solution and carbonic phase (with 89–99 mol. % CO₂ and 1–11 mol. % CH₄). The mineralization formed at temperatures of 200–320 °C and pressures 0.5–2.0 kbar. The elevated content of methane (up to 50 mol. %) in the sample SRS-14 can be related to the adjacent slightly metamorphosed Culmian flysch siliciclastics, or to retrograde hydration of host graphite phyllite. The vein morphology, presence of albite, rutile, and ilmenite, gold fineness, chemical composition of fluids, and interpreted PT conditions are all consistent with ore formation during a late phase of metamorphic reworking which occurred during the Variscan Orogeny in the given area. Pressure fluctuations suggest that the veins formed by crack-seal mechanism. The mineralizations from both studied sites represent temporary episodes in evolution of the ore mineralization in the Andělská hora Ore District.