Mapeamento geológico e petrografia das ocorrências de cobre da Bacia de Carnaubinha, Pio IX – PI.

Abstract

In recent decades, the rift basins of Borborema Province have been the subject of prospective studies on rocks rich in iron and copper contents. There is about ten rift basins in the Borborema Province, and most of them have record of iron and copper ocurrences. Some authors correlate the occurrences of these basins with mineralization in IOCG systems due to characteristics such as extensional setting, structural control, morphology, associated hydrothermal alterations, among others. The Carnaubinha basin is located in the Pio IX city, Piauí, and corresponds to a small eopaleozoic rift basin. It its inserted in the central-western portion of Borborema Province, far west of Orós Mobile Belt, in the Orós-Jaguaribe System. This basin corresponds to an immature clastic sequence deposited in an intracontinental rift on the Orós Group, which is formed by an association of metavulcanosedimentary rocks, which basement is constituted by orthogneisses of São Nicolau Complex. The sedimentary rocks from Carnaubinha basin are predominantly matrix-supported polimitic conglomerates, with interlevels of sandstone, shale and siltstone. This work presents a detailed mapping of the Carnaubinha Basin, aiming a better delimitation of its limits, the characterization of occurrences mineralized in copper and iron and of the hydrothermal alterations in the area. The rocks from the basin and in the adjacent basement are affected by hidrotermal alteration and its been found records of mineralizations in iron and copper associated with the silicified zones. In the location, hydrothermal alterations such as K-feldspatization, carbonitization, silicification, epidotization, chloritization and sericitization have also been described. These characteristics allow to correlate the mineralizations studied in this work with IOCG type deposits. Also, the presence of alterations described as shallow and distal in these deposits allow us to infer that these occurrences are part of a larger hydrothermal system, correlated to those described in other eopaleozoic rift basins such as Jaibaras and Cococi.