Datation Re-Os sur pyrite et traçage des sources des métaux dans des gisements de type porphyre et épithermal neutre : exemple des gisements de Bolcana, Troita et Magura, Monts Apuseni, Roumanie

Abstract : Many porphyry-type and neutral epithermal ore deposits related to a neogene andesitic volcanism are encountered in the Apuseni Mountains. To study possible genetic relationships between the porphyry-type and neutral epithermal deposits, the Bolcana porphyry has been investigated since it is surrouded by a number of epithermal low-sulfidation veins with a Pb-Zn ± Au mineralization (Troita and Magura). In order to establish the temporal relationship between the different ore deposits, a Re-Os dating method has been developped and applied on pyrite. This method enabled us to assign an age of 10.9 ± 1.9 Ma for the porphyry-hosted mineralization. The ages obtained for the epithermal systems are somewhat approximative as perturbations of the Re-Os system are observed for these environements. A fractionation of rhenium and arsenic responsible for a significant enrichment in these elements for the apical zone of the porphyry has been demonstrated. This enrichment is most probably related to a maximum boiling event. The sources for the metals have been characterized by combining two isotopic systems (Re-Os and Pb-Pb) on both pyrite and galena. The osmium data indicate that the Troita deposit has composition which is similar to that of the Bolcana porphyry. In constrast the results obtains for the Magura deposits indicates the Re-OS system has in this case been perturbed due to a weathering of nearby ophiolites which probably contributed some osmium to the pyrite at Magura. Additional results obtained for common lead seem to confirm the osmium data, with an osmium isotopic composition which has a more important mantle-derived component than at Troita.
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Olivier Cardon. Datation Re-Os sur pyrite et traçage des sources des métaux dans des gisements de type porphyre et épithermal neutre : exemple des gisements de Bolcana, Troita et Magura, Monts Apuseni, Roumanie. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10130⟩. ⟨tel-01748279⟩

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