ORIGIN OF THE CHARMITAN GOLD-QUARTZ DEPOSIT (UZBEKISTAN)

Data on fluid inclusions and stable isotope composition, analysis of m ineral assemblages, and thermodynamic calculations are used to work ou t a genetic model for the Charmitan gold-quartz deposit. The ores of t he deposit precipitated at temperatures from 400 to 150 degrees C, und er pressures of 2.77-0.9 kbar, from fluids with pH similar to 5 +/- 1. The oxygen fugacity did not exceed the values typical of a pyrite-pyr rhotite-magnetite buffer (10(-38) to 10(-29) bar), the sulfur activiti es were 10(-8) to 10(-20), CO2 fugacities varied from 10(2.6) to 10(1. 5) and CH4 fugacities ranged from 10(1.5) to 10(2.6) bar. The minerals crystallized from fluids of various compositions: (a) H2O-rich CO2- a nd CH4-bearing fluid with dissolved chlorides (1.5-15 wt % equiv. NaCl ), (b) vapor-rich fluid composed of CO2, CH4, and (c) aqueous-saline f luid with a salinity up to 10 wt % equiv. NaCl. The occurrence of syng enetic liquid-rich and vapor-rich inclusions is evidence of the immisc ibility of the initial fluid into two fluids at the earliest productiv e stages. The delta(18)O, delta(13)C and delta(34)S of fluids were cal culated to be +1.6 to +6.6 parts per thousand, -0.6 to -17 parts per t housand, and +2.6 to +10.7 parts per thousand, respectively. These var iations suggest a mixing of fluids from different sources. According t o the proposed genetic model, fluids and components of magmatic origin dominated during ore formation, but those derived from metamorphic de hydration and decarbonatization of host rocks also participated.