Refined timing of porphyry copper formation in the Serbian and Bulgarian portions of the Cretaceous Carpatho-Balkan belt
Résumé
he Bor district in Serbia and the Panagyurishte district in Bulgaria are part of the mineralized Late Cretaceous Carpatho-Balkan igneous belt. 40Ar/39Ar laser probe radiometric age information from porphyry copper deposits of the two districts in this study provides new constraints on the timing of host-rock emplacement and the hydrothermal alteration that is linked to the porphyry mineralization. In the Bor district, igneous hornblende from the host intrusions has an average plateau age at 84.0 ± 1.5 Ma (2σ). The timing of alteration is constrained by white mica with an average inverse isochron age of 85.4 ± 1.8 Ma and an average plateau age at 86.6 ± 1.0 Ma (elevated by a small excess 40Ar contribution). Together, these analyses indicate that porphyry mineralization occurred around 85 Ma. In the Panagyurishte district previous isotopic studies have produced much older host-rock ages in the northwest than mineralization ages in the southeast. Ages of igneous and alteration mineral separates from Elatsite and Medet in the northwestern and central parts of the district from the present study confirm pluton emplacement at 90.8 ± 0.8 Ma but much younger alteration at 79.5 ± 0.5 Ma. It is proposed that two episodes of magmatic-hydrothermal activity have affected the district, one at ~91 Ma, with the emplacement of the majority of the plutonic rocks, and one at 79 to 80 Ma during which the alteration micas were reset. Integration of these new ages with existing radiometric age information emphasizes the complex history of magmatic-hydrothermal activity along the immature Late Cretaceous Carpatho-Balkan convergent margin.