Characteristics and origin of polymetallic mineralisation in the Kopaonik region of Serbia and Kosovo, with particular reference to the Belo Brdo Pb-Zn (Ag) deposit
This project was initiated with the aim of determining the origin and evolution of the Belo Brdo Pb-Zn (Ag) carbonate-replacement and vein-type deposit in the Kopaonik metallogenic district of Serbia and Kosovo and to test its potential genetic association to nearby porphyry Cu-Au and skarn deposits. Hydrothermal-replacement, stockwork, skarn and vein-type base metal deposits in the region are related to a Tertiary (65.5 to 1.8 Ma) volcano-magmatic complex that intruded a tectonic nappe pile that includes a Triassic (251-199.6 Ma) Metamorphic Complex, a Jurassic (199.6 to 145.5 Ma) Ophiolite Unit and an Upper Cretaceous (99.6 to 65.5 Ma) Flysch Unit. Petographic and geochemical investigations of the Tertiary igneous rocks confirm a calc-alkaline chemistry for regionally distributed andesitic-dactic and quartz-latite rocks. These volcanic rocks show a clear subduction-related character. The Pb-ZN (Ag) minerlaisation at Belo Brdo evolved as a result of several successive stages of mineralisation includeing: (1) pre-ore stage, including early hydrothermal alteration and listwanisation followed by the deposition of Ni-Co-As sulphides; (2) main-ore stage, represented by massive sulphides including sphalerite, galena, pyrite, arsenopyrite, chalcopyrite, Ag-tetrahedrite-tennantite, bournonite; and (3) post-ore stage represented by quartz, carbonates + pyrite. A combination of fluid inclusion microthermometry, sphalerite and arsenopyrite geothermometry, and oxygen-isotype geothermometry suggests that the hydrothermal mineralisation at Belo Brdo was deposited from epithermal- to monderately high temperature (160-350[degrees]C), low salinity (6.5 eq. wt. % NaCl) fluids. Calculated [delta][sup]18O (6.5 to 10 ‰) and [delta]D (- 38 to - 62 ‱) values of water in equilibrium with sericite, tourmaline and quartz of the pre-ore stage are consistent with the ore fluids being derived from a magmatic source. Additionally, calculated oxygen isotopic composition of the main-ore stage fluid shows magmatic signatures (5.9 to 7.7 ‰). However, the water from fluid inclusions hosted by quartz from the late- ore stage breccia exhibits lower [delta]D (-93 to -96 ‰) and [delta][sup]18O (4.8 to 2.3 ‰) values, indicating an involvement of a more dilute, low-temperature meteoric hydrothermal fluids, Meteoric water played an increasing role toward the later stages of ore deposit evolution. The [delta][sup]34S values of the sulphides at Belo Brdo are homogeneous (average 4.4‰) and similar to those from nearby Cu-Au porphyry and skarn deposits in the study area, indicating a common source of sulphur for all deposits. The hydrothermal deposits in the study area show homogenous lead isotopic compositions ([sup]206P/[sup]204Pb= 18.68 to 18.76, [sup]207Pb/[sup]204PB= 15.67 to 15.68, and [sup]208Pb/Pb = 38.87 to 38.91), similar to those of local calc-alkaline volcanic rocks ([sup]206Pb/Pb - 18.76-18.82, [sup]207Pb/Pb 15.66-15.68 and [sup]208Pb/[sup]204Pb 38.87-38.97 indicating a genetic link between minerlisation and magmatism. The data suggests that the Belo Brdo and the nearby Pb-Zn deposits are not Mississippi Valley type, but similar to a high temperature carbonate-replacement massive sulphide deposits associated with calc-alkaline magmatism in a supra-subduction zone setting.