Microthermometric, laser raman spectroscopic, and volatile-ion chromatographic analysis of hydrothermal fluids in the paleozoic Muruntau Au-Bearing quartz vein ore field, Uzbekistan

Fluid inclusions in quartz and scheelite from flat, steeply dipping central , and stockwork-type quartz veins within the Muruntau Au-bearing quartz vei n ore field have been investigated in a reconnaissance study, using fluid i nclusion mapping, microthermometry, laser Raman spectroscopy, and integrate d gas and ion chromatography fur bulk volatile and cation-anion analysis. M uruntau central veins are dominated by inferred early CO2-bearing fluid inc lusions. In contrast, flat quartz veins contain considerable numbers of low -density, pure aqueous inclusions on deformation- and recrystallization-rel ated microstructures. Fluid phase separation is indicated for samples from te Muruntau central ore veins by fluid inclusion observational work, as wel l as by microthermometry and bulk fluid geochemistry (CO2/CH4, CO2/N-2, and CO2/C-2-, and C-3- hydrocarbon ratios; salinity data). However, in flat ve ins and all samples from the Myutenbai deposit no evidence for fluid immisc ibiliy could be found. Quartz microstructural results and fluid inclusion d ata suggest formation of the low-grade mineralized flat veins before the ma in stage of hydrothermal activity and considerable variation in the geochem ical conditions during fluid evolution in the Muruntau and Myutenbai deposi ts. Mixing of fluids from different sources in variable proportions may be inferred from halide geochemistry. Furthermore, fluid inclusion Br/Cl ratio s differ significantly for samples from differ ent vein types. Fluid phase separation is suggested as a mechanism for the precipitation of Au from the hydrothermal fluid in the Muruntau high-grade hu mineralized central veins .