The graphite mineralization in the Aracoiába-Baturité District (CE): Geotectonic and metallogenetic implications

Abstract

In the Aracoiába-Baturité region, the Baturité Subunit (Ceará Group) was divided into Baturité I and II domains. The Baturité I Domain comprises a supracrustal sequence, formed in an environment corresponding to a continental slope, overlying Paleoproterozoic rocks of the Gneissic-Migmatitic Complex. The graphite bearing aluminous gneisses associated with the Baturité I Domain were compared with those found in Khondalite belts from different parts of the world. The Baturité II Domain was formed in the foot of a slope-abyssal plain facies of a deep sea, and is associated with ortho-amphibolites and metaturbidites. Occurrences of graphite are distributed from Aracoiába to Canindé region, following the Baturité Subunit, defining an important regional metallotect. Graphite deposits are of two types: graphite gneiss (disseminated graphite) and veins (massive graphite) and have different genetic origins (epigenetic and syngenetic). ?13C values between -30 and -20% indicate that graphite is derived from organic matter. The epigenetic mineralization is found in the vicinity of Pedra Aguda plutonic body (Pedra Aguda Gabbro-Diorite Complex) within a maximum distance of 2.5 km. The graphitic belt of the Aracoiába-Baturité District was regarded as a remnant of a subduction zone/suture zone derived from the process of closing of an ancient ocean with the consequent gluing of two continental micro-cratons (Baturité Block in the north and Caio Prado Block in the south) during the Brazilian orogeny.