MINERALIZING FLUID COMPOSITION AND GENESIS OF GOLD-SULFIDE-TELLURIDE MINERALIZATION AT THE MEGRADZOR DEPOSIT: EVIDENCE FROM FLUID INCLUSIONS

Abstract

Evidence provided by fluid inclusions points to a broad interval of physical conditions and fluid compositions at which the mineralization was produced: temperatures of 360-132 degreesC, pressures of 2180-130 bar, fluid salinities of 18.5-1.4 wt % equiv. NaCl, 5.7-0.9 mol CO2/kg of solution, and 4 x 10(-2) to 10(-2) mol H2S/kg of solution. The solutions are determined to contain Cl (0.77-0.24 mol/kg of solution), Na (0.7-0.3 mol/kg of solution), and K (0.14-1.5 x 10(-3) mol/kg of solution). Thermodynamic calculations indicate that the most probable deposition factors of metals early in the mineralizing process were an increase in the pH and a decrease in the temperature, perhaps, due to the ascent of the mineralizing solution and its mixing with meteoric waters. The origin of the telluride mineralization was controlled by the involvement of fluids of other geneses (probably related to connate solutions) into the hydrothermal system. The early hydrothermal mineral assemblages are demonstrated to have been formed at relatively high temperatures and pressures by fluids compositionally most close to magmatic fluids. Gold-bearing mineral assemblages were deposited in environments most close to epithermal systems. The fact that gold-bearing mineral assemblages inherit certain features from early assemblages suggests that the Megradzor deposit was produced with the participation of deep-seated fluids.