At the Gerfed gold deposit, fluid inclusions were studied by thermobarometry, gas chromatography, Raman spectroscopy, and ICP MS in quartz samples of three types: quartzites, Au-poor (<1–2 ppm) feathering veins, and Au-rich (>2.8–10 ppm) feathering veins. It has been found that these three types were produced from fluids differing in composition and thermobarogeochemical parameters. The quartzites formed from low-salinity (<7.0 wt.% NaCl equiv) homogeneous fluids of essentially aqueous–chloride composition at 120–230 °C and 0.1–0.5 kbar. The gas phase in these fluids comprises H2O, CO2, CH4, and N2, with CO2/(CO2 + H2O) = 0.04–0.15 and CO2/CH4 = 2.2–3.8. The Au-poor feathering veins formed from homogeneous and heterogeneous fluids at 150–300 °C and 0.5–2.0 kbar. The salinity of the fluids increased to 10 wt.% NaCl equiv. The gas phase in them comprises H2O, CO2, N2, and CH4. Here, CO2/(CO2 + H2O) = 0.09–0.17 and CO2/CH4 = 2.2–2.3. The Au-rich feathering veins formed from heterogeneous and more saline (6.0–23.3 wt.% NaCl equiv) CO2–H2O fluids at higher temperatures (150–400 °C) and pressures (1.1–2.5 kbar). In this fluid CO2/(CO2 + H2O) = 0.18–0.27 and CO2/CH4 = 4.1–20.8. All three quartz types show negative Eu anomalies and a distinct predominance of LREE over HREE. Differently directed trends of REE and Eu/Sm in the quartzites and feathering veins suggest that the fluids were produced from different sources. The fluids of the gold-bearing quartz veins are enriched in K, Li, and Rb, and those of the Au-poor feathering veins, in Sr and Na. The quartzites have low Rb and Sr and similar Na and K contents. Areas with a high and bonanza gold content in feathering-vein stockworks formed when high-temperature saline H2O–CO2 fluids were superposed on the Au-poor quartzites and feathering veins.

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