Classificação de pegmatito no distrito de Ipojuca na cidade de Crateús-Ceará

Abstract

The location of the study area for this work is located at a distance of 15 km from the city of Crateús and is delimited by three geographic faults, two of which are oriented southwest (SE) and the third oriented towards Northeast (NE). It is observed that the pegmatites are in the contact zone between the Tamboril Santa Quitéria complex (NP3ts) and the Canindé do Ceará Complex (PRcn) where contact failure occurred. In the search for pegmatites in the district of Ipojuca in Crateús-Ceará and their classification according to Johnston, 4 (four) distinct pegmatitic bodies were observed. As methodological steps were carried out the definition of the study area, collection of samples with trench opening and identification of the main minerals present. After the collection of samples, 3 (three) were chosen for analysis of ICP-OES and Infrared Spectroscopy, two garnets with different colors (orange red and black) and a beryl aiming at the identification of the elements present. Local radiation detection analysis was carried out in the main pegmatitic outcrops using a Geiger counter. The results of the measurements, on the surface of the outcrops, showed low levels of radiation, with average values of the order of 00,150 μSv/h. The results of chemical analysis by ICP-OES identified the presence of 13 (thirteen) elements present Al, B, Ba, Ca, Fe, Pb, Mg, P, Na, K, Se, Mn and Zn in the analyzed samples of garnets and 8 (eight) elements in the analyzed beryl sample Al, Be, Ca, Na, Mn, Mg, Fe and K, and the presence of Mn and Fe metals are responsible for the characteristic colors of the samples. The infrared spectra were compared for the two samples with different garnet, red and black colors, noting that they have a similar chemical structure as suggested by the literature A3B2(SiO4)3 (where A and B are the substituting elements of Ca, Al , Mn, Mg, Fe and Zn). The results of infrared spectroscopy for the bands at 3600 and 3698 cm-1 in the beryl sample were compared with data from the literature and indicate the presence of Na+ and K+ ions interacting with water molecules in their interstices. The pegmatitic bodies studied in this work are indicative of heterogeneous characteristics as described by Johnston, 1945. The parameters analyzed testify to future research and exploitation of these minerals present in the Ipojuca pegmatite.