Mapeamento geológico e das alterações hidrotermais associadas às ocorrências de ferro na região de Pio IX - PI

Abstract

IOCG-type deposits attract attention in mineral exploration and academia, especially after the discovery of the Olympic Dam deposit (Australia). These deposits contribute for a large part of the world's copper reserves, and show significant contribution in by-products such as iron and gold. The potential of Borborema Province for the exploration of these deposits was always underestimated due to the intense deformation in the Neoproteorozoic, since these deposits are commonly associated with extension tectonic environments. However, in the region of Pio IX (PI), there are several occurrences of iron in the form of hydrothermal breccias hosted by different host rocks, with no evident record of ductile deformation. Such occurrences have already been subject of mineral research by the Australian company Western Mining Corporation in 1990’s. These occurrences are located in the center-west portion of the Borborema Province, southwest of the Upper Paleoproterozoic Orós Mobile Belt, in the OrósJaguaribe Domain. The geology of the region is marked by a metavulcanosedimentary association constituted by metapelites, metavulcanic rocks, marbles and calcissilictic rocks, produced by greenschist facies metamorphism, belonging to the Orós Group, and its basement, represented by gneissic associations, variously migmatized, with granodioritic to tonalitic composition, formed by metamorphism in the amphibolite facies, belonging to the São Nicolau Complex. Brasiliano-age granitoids intruded all these sequences. The lithological association that hosts the breccias is controversial, and there have been no studies to characterize and map hydrothermal alterations and their relation to the formation of these breccias. This work focused on the description of the occurrences of hematite breccias and on the characterization of the associated hydrothermal alterations in temporal and spatial character. The mapping allowed to identify the occurrence of hydrothermal breccias subdivided into hematite and silicious breccias, both with associated sulphides, locally, malachite disseminations occur, as well as epidote breccias. Alterations were described as albitization, K-feldspatization, epidotization, silicification and hematization. The characterization of the different breccias and associated hydrothermal alterations indicate that these occurrences have a number of characteristics common to IOCG type deposits, evidenced especially by the mineral associations typical of hydrothermal alterations in deposits of this type. The occurrence of these breccias rich in iron oxides, with associations of sulphides and evidence of copper mineralization extends throughout all the Eopaleozoic basins, from Jaíbaras to the north, to the basins of São Julião/Catolé south of Pio IX, suggesting that these occurrences are part of a continental scale hydrothermal system.