Rapakivi granites and related rocks of the São Lourenço-Caripunas intrusive suite (1.32 - 1.30 Ga) at the São Lourenço-Macisa mining district, NW part of the Rondônia tin province: I - Petrography of the early facies and evidence of magma interaction

Abstract

The São Lourenço-Caripunas Intrusive Suite (1.32 - 1.30 Ga) at the São Lourenço-Macisa mining district (NW part of the Rondônia tin province) includes rapakivi granites and related rocks, which are grouped in four igneous units mapped on a scale of 1:25,000. Unit A is composed of biotite-hornblende wiborgites and pyterlites and seriate biotite granites; unit B corresponds to granites porphyries with hornblende and/or biotite; and unit C is composed of gabbros, microgabbros, hornblende quartz monzonites and granites porphyries. The lithotypes of units A, B, and C are interpreted as early intrusive phases, whereas the unit D lithotypes are interpreted as late intrusive phases and spatially related to primary tin deposits and associated metals. Some early petrographic facies show assemblages of minerals and textures that suggest interaction processes of more mafic and more felsic magmas in the origin of these rocks.