Geocronologia PbPb TIMS de sulfetos do depósito do tipo VHMS da Fazenda Coqueiro Cráton do São Francisco NE do Brasil: implicações sobre a idade e a gênese da mineralização de ZnPb

Abstract (English)

TIMS Pb-Pb geochronological data allow determination of the timing and genesis of the Fazenda Coqueiro volcanic-hosted massive sulfide (VHMS) Zn-Pb deposit hosted in the Neoarchean Mundo Novo greenstone belt (MNGB), NE São Francisco Craton. The deposit is inserted in the Rhyacian-Orosirian Contendas-Jacobina lineament between Archean cratonic blocks. The basement of the deposit is composed of Paleoarchean metagranite and metarhyolite nuclei tectonically emplaced within the supracrustal rocks. The volcanic-sedimentary rocks comprise the ocean floor western metabasalt, calcsilicate rock, aluminous schist, metachert, banded iron formation, and tremolitite of the middle sequence and metasedimentary siliciclastic rocks of the uppermost sequence of the MNGB. The western metabasalt is hydrothermally altered, which resulted in the formation of two alteration zones. They consist of carbonate zone, proximal, hosting massive sulfides composed mainly of sphalerite and galena with minor chalcopyrite; and sericite-chlorite zone, distal, hosting mainly disseminated chalcopyrite. Pb-Pb galena, chalcopyrite and sphalerite data from the massive and disseminated zones in the Fazenda Coqueiro deposit yielded model ages of 2,804 ± 11.15, 2,794 ± 11.2, and 2,767 ± 11.1 Ma, respectively, with the Pb sourced from the upper crust, based on the uranogenic and thorogenic diagrams. The Pb-Pb isochron mineralization age of 2,747 ± 16 Ma obtained from chalcopyrite and sphalerite samples from the massive and disseminated zones suggests that the sulfides were coeval and do not record later metamorphic-hydrothermal events. Therefore, the Fazenda Coqueiro deposit would have formed from Neoarchean ocean floor volcanic-exhalative processes. The Rhyacian-Orosirian tectonic event compressed the deposit between Archean blocks along the Contendas-Jacobina lineament, preserving the sulfides from remobilization processes.