A fluid inclusion study of Au-W stratiform mineralization at Orlik near Humpolec, Czechoslovakia
Ďuršová, Jana; Sztacho, Petr; Dubessy, Jean
European Journal of Mineralogy Volume 4 Number 5 (1992), p. 965 - 976
published: Oct 14, 1992
manuscript accepted: Feb 4, 1992
manuscript received: Jul 16, 1991
ArtNo. ESP147050405017, Price: 29.00 €
Abstract Gold-scheelite mineralization occurs in polyphase, high-grade metamorphic rocks of the Moldanubicum in the core of the Bohemian Massif near the contact with the Variscan Central Moldanubian pluton in SE Bohemia. The stratiform ore-bearing zone is cross-cut by younger pegmatite veins of Variscan age. Fluid inclusions were studied by microthermometry and micro-Raman analysis in quartz, apatite and scheelite. H2O-CO2 fluids (CO2 < 50 mol.%, ch4 < 3 mol.%, n2 < 2 mol.%, and h2s -rich fluids (CH4 < 24 mol.% and n2 < 26 mol.%) with very low density (th ch4 (v) from -137.8 to -118.7 °c, d 2 kbar to < 1 kbar) and input of a new fluid (CH4-rich) along the tectonically weakened zone. Crystallization of scheelite (at T 360-390 °C and P < 0.7 kbar) was probably caused by the change of oxidation state (CO2 to CH4) in the ore-bearing zone. The precipitation of gold and maldonite (Au2Bi) occurred after scheelite crystallization at temperatures lower than 373 °C (the upper thermal stability of maldonite).