Geologia e Litogeoquímica das intrusões máficas-ultramáficas da região de Amajari, Roraima: implicações petrogenéticas

Abstract

In the northern state of Roraima, western portion of Surumu Domain occur several mafic-ultramafic intrusions associated with granitic calc-alkaline rocks and metasedimentary paleoproterozoic. Some of these intrusions, correlated to suite Uraricaá, located next to the Amajari city, were the object of study of this work. This work investigated the geological context, tectonic and metallogenic potential of mafic-ultramafic intrusions. The methodology consisted of geological mapping; light petrography bent and transmitted, in whole rock geochemistry, petrogenetic modeling, metallogenic research. Six semicircular bodies were mapped with a diameter of up to 4 km, which intrude the granitic of Pintada Pintada Suite, comprising olivine-websterites, olivine norite, olivine-enstatite-gabbro, enstatite-gabbro and gabbronorites, predominantly cumulate texture, and subophitic locally. The rocks exhibit no macroscopic structure or feature deformation and / or hydrothermal. The main observed mineralogy was olivine crystals, enstatite, augite and labradorite, with rare crystals of pyrite, chalcopyrite and magnetite. However, a newly formed mineralogical assembly composed of hornblende + chlorite ± ± actinolite coil was observed, leading to static low-grade metamorphism, possibly correlated to K'mudku Event. The rocks have tholeiitic affinity and sub-alkaline, with wide variation in MgO (5% -23%) and low TiO2 (<1.2%). The behavior of the higher oxides, minor and trace elements throughout the crystallization process these rocks; have been expected in relation to the compatible and compliant behavior. It were identified in these rocks one magmatic arc signature, evidenced by the low enrichment of Nb and Ti, with different levels of LREE fractionation compared to HREE, with two distinct patterns, a sub-rectilinear and another inclined. The research on the type of magmatic source, it was concluded that there was a possible mix of sources E-MORB and N-MORB, with oceanic lithosphere subducted contribution in a magmatic arc environment. Already petrogenetic modeling concluded that these rocks are congenetics each other, through the process of AFC, with the contaminants rocks the granitic of Pedra Pintada suite. Regarding the economic potential, it can be said that from the values of Ni, Cu, Cr, Pt, Pd and Au, the studied rocks have no need enrichment as to consider them mineralized, with no stage been found sulfide representative and that the anomalies present in bateia concentrate and soil are the product of later supergene processes on these rocks.