Abstract:
New data are reported on the concentration of oxidized and reduced N and C species in solutions from fluid inclusions in gangue quartz from gold deposits of various types. At all deposits, the solutions are composed of water and carbon dioxide. The CH4 amount is 1-2 orders of magnitude lower than that of CO2, whereas ammoniacal forms are the prevalent nitrogen species. A direct relationship between CO2/CH4 and N2/NH3 is observed at the Charmitan and Zod deposits hosted in igneous rocks. At the Muruntau and Marjanbulak deposits localized in carbonaceous sedimentary rocks, the NH3 content in fluid increases with enrichment in CO2. Thermodynamic analysis shows that equilibrium between C- and N-bearing species in fluids was not achieved at the deposits under study, probably, because of their relation to different sources. A temperature range of 200-300°C is most favorable for the formation of ammonium-bearing micas, which are depleted in ammonium at a higher temperature. In addition, the low temperature hampers ammonium oxidation to nitrogen. This controls the concentration of ammonium in solutions and minerals related to the low-temperature metamorphism and hydrothermal alteration of sedimentary rocks enriched in organic matter.