Origin and Evolution of Ore-Forming Fluids at the Small-Sized Gold Deposits in the Khudolaz Area, Southern Urals

Lode gold deposits are widespread in orogenic belts of various ages and a valuable source, but their genesis remains debatable. The close relationship between native quartz was considered reason to search for acid-magmatic sources heat fluids (i.e., granite intrusions), while small gabbro bodies were often ignored. Six minor associated with NE-strike faults studied the Khudolaz area South Urals (Tukan, Bilyan-Tau, Fazly-Tau, Muildy-Tamak, Alasiya-II Isyanbet-I). It established, first time, that all similar geologically differ mineralogical diversity ore-bearing veins, which is due different composition host rocks intrusions (325–329 Ma, U-Pb) Ulugurtau (321 ± 15 Sm-Nd) ultramafic-mafic complexes. Results geochemical study veins (ICP MS) fluid inclusions (microthermometry, gas chromatography) showed mostly precipitated at temperatures 230–330 °C from low- moderate-saline (8–12 wt.% NaCl-eq.) H2O–CO2–CH4-bearing fluid, when weakly oxidized or near-neutral conditions, replaced by reducing ones. No significant differences barren milky white brownish defined, indicates common formation settings an impulse pattern vein injection. stable salinity, along low hydrocarbon N2 contents, as well narrow range δ18O values, indicate prevailing magmatogenic source certain influence without meteoric waters. Based on presented data, attributed epizonal type. This shows lode possible participation massifs.