MINERALOGY AND FLUID INCLUSION STUDY OF THE ZIDAROVO COPPER POLYMETALLIC DEPOSIT, EASTERN BULGARIA

The Zidarovo polymetallic deposit is genetically related to trachyande sites and trachybasalts of Upper Cretaceous age. Four stages of vein t ype ore mineralization have been established; they carry the following mineral assemblages: 1. quartz-pyrite; 2. chalcopyrite-bismuthinite ( including first generation gold and electrum); 3. hematite-chlorite; 4 . galena-sphalerite (including a second generation of gold and electru m). Specific to Zidarovo are Bi-bearing (Bi up to 11.22 wt.%) zincian tetrahedrite and tennantite, which were deposited in the second and fo urth stage of mineralization. Mineralogical data suggest that silver w as enriched in hydrothermal fluids during the last stage of mineraliza tion. Fluid inclusions in quartz show gradually decreasing formation t emperatures from early (371-310 degrees C) to late (292-197 degrees C) stage of mineralization. The lowest temperatures (150-120 degrees C) were obtained for sphalerites of stage four. The overall low salinitie s of the fluids (on average: 4.0 eq. wt.% NaCl) suggest that meteoric water was involved in mineralization. The possibility of interactions between ascending hydrothermal fluids and dilute meteoric waters is su pported by geological features and mineralogical data which indicate a shallow depth of mineralization.