engleski

P-T-X conditions of mineralizing fluids from Pb-Zn-Ag hydrothermal-metasomatic deposit Stari Trg, Trepè a, Kosovo

Stari Trg mine (42.9°N, 20.9°E), Trepa, is located 35 km NW from Pristina, Kosovo. The deposit is related to intensive Late Palaeogene post-collisional magmatism within the Western ophiolitic Vardar zone in the Dinaride Alpine Belt. Mineralization represented mainly by galena, sphalerite, pyrite, arsenopyrite and pyrrhotite, is hosted in mramorized limestones with developed paleokarst and covered by Triassic schists. The major gangue minerals are carbonates and quartz. Commonly skarn minerals antecede sulfide mineralization. In the upper levels, nearly circular quartz-latite and breccia pipe transects the limestone-schist contact along the crest of the anticline. Breccia is composed of subangular fragments of the country rocks, rounded fragments of quartz-latites and contains pyrrhotite and pyrite mineralization. In the deeper levels breccia cuts limestones and occasionally has characteristics of fluidized breccias with milled matrix. The P-T-X conditions during mineralization were determined by combination of fluid inclusion (FIs) data and sulfides geothermometry. FIs studies were carried out on skarn (hedenbergite), sulfide (sphalerite) and gangue (quartz, carbonate) minerals. The main dissolved salts are NaCl and CaCl2, and FIs related to skarn parageneses contain KCl as well. FIs from hedenbergite represent high temperature (Th=385- 410°C) and moderate saline (14.8-16.5 wt.% NaCl equ.) magmatic fluid. Lower salinity (8.0-14.6 wt.% NaCl equ.) and lower Th (240-305°C) from FIs within dark sphalerite suggest mixing of hot, saline magmatic with cold, diluted meteoric fluid. The presence of marcasite points to acidic environment. The formation temperature for the sulfide mineralization defined from the chemical composition of arsenopyrite co-existing with pyrite and sphalerite is 360º C. The chemical composition of sphalerite in equilibrium with pyrite and pyrrhotite points to a formation temperature between 380 and 405°C. The pressure range from 1 to 1.25 kbars was determined by combination of FIs data and the sphalerite geothermometer. FIs from gangue minerals (5.7- 10.7 wt. % NaCl eq., Th=270-355°C) support the fluid mixing as the major precipitation mechanism. Deposition of carbonates requires higher pH of fluids. Geological setting and geochemical investigations characterize the Stari Trg mineral deposit as calcic Pb-Zn-Ag skarn deposit. The prevalence of carbonate host rocks and presence of gangue coarse-grained, iron-rich mixture of Ca-Mg-Fe-Al silicates (skarn minerals) differentiate this deposit from the other contemporaneous deposits in the region. FIs studies recognized three major stage of mineralization: 1. metasomatic formation of skarn minerals from fluid of magmatic origin ; 2. precipitation of ore minerals caused by mixing of magmatic and meteoric fluids and 3. deposition of gangue carbonates and quartz from diluted and neutralized fluids.

Pb-Zn-Ag deposits; hydrothermal-metasomatic; Neogene vulcanism; fluid inclusions; skarn

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