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

Autori
Strmić Palinkaš, Sabina, Palinkaš, Ladislav, Lüders, Volker, Molnar, Ferenc

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Architecture of collisional orogens / Franz Neubauer - Salzburg, 2007, 71-72

Skup
Austria-China workshop: Architecture of collisional orogens

Mjesto i datum
Salzburg, Austrija, 13.09.2007. - 15.09.2007

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Pb-Zn-Ag deposits; fluid inclusions; Kopaonik; Neogene volcanism

Sažetak
Stari Trg mine (42.9°N, 20.9°E), Trepča, is located 35 km NW from Priština, Kosovo. The deposit is related to intensive Miocene syncollisional magmatism within the Western ophiolitic Vardar zone in the Dinaride Alpine Belt (Fig. 1). The geological formations consist of schist, phyllite, quartzite and mramorized limestones of Triassic age (Stari Trg series). The principal mineralized stratum is limestone with developed paleokarst. The Stari Trg Series is unconformably overlain and partly obscured by andesite flows and tuffs of Miocene age. The older rocks of the region are strongly folded. An anticlinal structure, along which mine is developed, plunges about 40°NW. A nearly circular sanidine-dacite and breccia dyke transects the limestone-schist contact along the crest of the anticline (Fig. 1). At the surface and in the upper levels of the mine, the dyke contains a core of sanidine-dacite surrounded by a mantle of breccia. The dyke/stock terminages at depth and is absent in the lower levels of the mine. In the upper levels breccia is composed of subangular fragments of the country rocks and rounded fragments of dacite. In the deeper levels breccia cuts limestones and has characteristics of fluidized breccias with milled matrix (Forgan, 1949 ; Schumacher, 1954). Galena, sphalerite, pyrite, arsenopyrite and pyrrhotite constitute the primary ore mineral assemblage. Commonly skarn minerals (ilvaite, hedenbergite, garnet) precede sulfide mineralization. The major gangue minerals are carbonates with variable cation composition (calcite, kuthnohorite, rodochrosite, siderite) and quartz. The P-T-X conditions during mineralization were determined by combination of fluid inclusion (FIs) data and sulfides geothermometry. Fluid inclusion 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 (homogenization temperature (Th) between 385 and 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 (11.4 &#177; 0.8 wt.% Fe) suggest mixing of hot, saline magmatic with cold, diluted meteoric fluid. The presence of marcasite points to acidic environment. A negative thermal gradient of approximately of 20°/m between level X. (+75m) and V. (+375m) is estimated according to FIs data from sphalerite. The formation temperature for the sulfide mineralization defined from the chemical composition of arsenopyrite co-existing with pyrite and sphalerite (level X., +75m ; 38 atomic % Fe, 34 atomic % As, 28 atomic % S) is 360&#186; C. The chemical composition of sphalerite in equilibrium with pyrite and pyrrhotite (0.03 mol.% CuS) points to a formation temperature between 380 and 405°C. The pressure range from 1 to 1.25 kbars was determined by combination of fluid inclusion data and the sphalerite geothermometer. FIs from gangue minerals with salinity between 5.7 to 10.7 wt. % NaCl eq. and Th in an interval from 270 and 355°C support the fluid mixing as the major precipitation mechanism. Deposition of carbonates requires higher pH of fluids. Boiling effects noticed in the carbonates from level VII. (+255m) (liquid-rich FIs: 9.2-10.0 wt. % NaCl equ. and Th=294-315°C, vapor-rich FIs: Th=290-318°C) indicates to formation temperature between 294 and 318°C. Determination of formation pressure is disable due to presence of CO2 (<5 mol. %). Geological setting and geochemical investigations characterize the Stari Trg mineral deposit as calcic Pb-Zn-Ag skarn deposit (e.g. Einaudi et al., 1981). 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 (hedenbergite) 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.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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