~(40)Ar/~(39)Ar geochronology of gold mineralization in Brasiliano strike-slip shear zones in the Borborema province, NE Brazil

摘要

~(40)Ar/~(39)Ar geochronology of muscovite and biotite grains genetically related to gold and Be-Ta-Li pegmatites from the Serido Belt (Borborema province, NE Brazil) yield well-defined, reliable plateau ages. This information, combined with data about paragenetic and field relationships, reveals Cambro-Ordovician mineralization ages (520 and 500-506 Ma) for the orogenic gold deposits in the Serido Belt. Biotite ages of 525 ± 2 Ma, which represent the mean weighted results of the incremental heating analysis of six biotite single crystals, record the time of pegmatite emplacement and reactivation of Brasiliano/Pan-African strike-slip shear zones. These results, along with previous structural evolution studies, suggest that shear zones formed during the Brasiliano/Pan-African event were reactivated in the Upper Cambrian-Lower Ordovician. Mineralization occurs late in the history of the orogen.