Intrusões máficas-ultramáficas do domínio Rio Grande do Norte, província Borborema : ambiente tectônico e potencial para depósitos magmáticos

A recently identified 32 km long NNE-SSW trending array of mafic-ultramafic intrusions in the paleoproterozoic Rio Piranhas terrain, Rio Grande do Norte domain (Borborema Province). The cluster of mafic-ultramafic intrusions described in this study provides a new window for exploration for Ni-Cu-(PGE) deposits in the Borborema Province. The mafic-ultramafic intrusions outcrop as small lensoid bodies (< 500 meters long) hosted mainly by orthogneiss and migmatites. Mafic-ultramafic rocks of four intrusions investigated in detail consist of variable proportions of wehrlite (Ol + Cpx ± Chr cumulate), clinopyroxenite (Cpx cumulate) and troctolite (Ol + Pl cumulate). The primary igneous textures and mineralogy are partially replaced by amphibolite facies metamorphic assemblages and tectonic fabric. These intrusions usually display mediumto coarse-grained domains where primary magmatic textures and minerals are preserved, and medium-to fine-grained massive to foliated texture where metamorphic fabric and minerals prevail. Primary magmatic features predominate in the core whereas a metamorphic minerals and texture characterize the contact with host rocks. The later consist of orthogneiss and migmatite associated with minor amphibolite and supracrustal. Metamorphic parageneses of banded orthogneiss, consisting of microcline-quartz-plagioclasehornblende, indicate amphibolite facies of metamorphism. The compositions of cumulate olivine in different intrusions and rocks types range from Fo80.6 to Fo67.6. The composition of the most primitive olivine in wehrlite indicates parental magmas with moderately primitive compositions (Fo80.6 and ~ 2,000 ppm Ni). The