GEOLOGIA DA OCORRÊNCIA DE COBRE DE MANDACARU (PI)

Abstract

The Mandacaru area, Sao Juliao County , Piaui, comprises a Precambrian crystalline basement of granitic to quartz dioritic gneisses overlain by several younger units of low grade metamorphic, volcanic and sedimentary rocks. The Late Proterozoic Sao Juliao sequence comprises folded epicontinental marine metasediments of low rank greenschist facies, including phyllite, marble, metarkose, and quartzite. The Eopaleozoic Catole Formation is represented by continental volcanic material (basalt, andesitic basalt, dacite, rhyolite, pyroclastics) and sedimentary rocks (conglomerate, arkosic wacke, feldspathic sandstone, siltstone), intruded by the post-tectonic Mandacaru Granite and related dykes and apophyses of granophyre, quartz porphyry and other felsic subvolcanic rocks. Eopaleozoic volcanism, sedimentation, and granite intrusion are controlled by faulting and graben-like structures, the evolution of which culminated with the deposition of polymictic conglomerate and breccia of the Tamborit Unit. Al1 the previous units are unconformably overlain by the Silurian Serra Grande Formation at the eastern border of the Parnaiba Basin. The Cu mineralization, probably of volcanic origin, is associated with the volcanic and sedimentary rocks of the Catole Formation, having been later convectively remobilized by water-rich fluids along minor faults and fractures within both the volcano-sedimentary pile and the granitic rocks during the Mandacaru Granite intrusion.