Geoquímica das laterais do domínio médio Coreaú - Noroeste do Estado do Ceará

Abstract

This paper makes an assessment of the geochemical signature of the lateritic rocks that occur near the towns of Granja, Martinópole and Parazinho northwest of the state of Ceara. Geologically the area is located in Médio Coreaú Domain, located in the northwestern portion of the Borborema Province, is characterized by the Granja Complex representing the basement of the region, composed of gneisses, granulites and migmatites, and supracrustal sequences composed by quartizitos, phyllites and schists of the Group Martinópole and Ubajara. The laterites occur forming a layer of weathering associated with phyllites, quartzites and gneisses and stand out to be an uncommon occurrence in areas considered semi-arid regions, where the most common would be associated with more humid climates (seasonal or not), so it is more likely that the process that led to the generation of these robes is due to different climatic conditions of the current old. The samples for geochemical analysis were collected at different points, where in each sample was collected from the source rock, the rock in the process of weathering and lateritic concretions in different lithologies in which the process is associated lateritization. The overall results show that in all the points considered, the contents of the oxides of iron and aluminum is higher, and the silica are lower than the bedrock, typical of a laterite profile. The H2O values also increased during the process and lateritization elements such as chromium, manganese, magnesium, sodium and phosphorus are stable. Taking into account the phyllite as source rock, it is observed that the enrichment in Al and Fe were found in the early stages of weathering, remaining stable during the process, as depletion of Si also followed this pattern of behavior. Iron was enriched in content of approximately 40% higher compared to the values shown in source rock. Considering the quartzite and gneiss in the increase of Fe content has become even more significant during the weathering process, with values greater than 70% of the rock in the process of change and of lateritic concretions. Results of X-ray diffraction show that the major oxides and hydroxides of the process are hematite and goethite in the oxidized sample stages silica is not present, in section 3 it is contained within the limit of concretionary nodules in training, this on a ledge mucking up the center. It can be considered by enriching the possibility of Fe mineralization, even though the enrichment of high-Al considered at all points where the contents of this element approximately estimated 6-7% of the rock in the process of change. However enrichment values are very significant Fe in the operation.