CHARACTERISTICS AND MINERALIZATIONS OF THE ARCHAEAN AND EARLY PROTEROZOIC OF THE BORBOREMA PROVINCE, BRAZIL

Resumo

Based upon its tectonic and magmatic mobilization, the Borborema Province is, by definition, a Brasiliano structural feature. Thus, the identification of Archean and Lower Proterozoic terrains is quite difficult still an aceount of the lack of sufficient geochronological data. For the most part of this province, the identification of such old terrains has been made by indirect and deductive reasoning, using mainly litho-structural and analogical criteria. Two fundamental kinds of terrains characterize this Province: a) Gneissic-Migmatitic terrains ("Massifs") where pre-Brasiliano Isotopic ages are more common, and b) metasedimentary and metavolcano-sedimentary Proterozoic terrains (so-called "Fold Belts"). The "massifs" include the majority of Archean and Lower. Proterozoic lithological sequences. No important mineral deposits are known in these massifs. However, closely associated with the mafic and ultramafic rocks are 40% of the tale and asbestos occurrences of this Province, as well as the Chromite deposit of Tróia, in the State of Ceara, and several interesting occurrences of Fe-Ti-V. On the other hand, sedimentary and volcanosedimentary processes were responsible for about 35% of the banded iron formations in the region, as well as for enclosing rocks of some gold mineralizations elsewhere.