Mineralogia, geoquímica e minerais pesados do perfil laterito-bauxítico com cobertura e sua relação com o grupo Itapecuru: lavra piloto ciríaco (Rondon do Pará)

Abstract

The lateritic-bauxite profile studied in Rondon do Pará is part of the Paragominas Bauxite Province, the most important of the Brazil that hosts world-class deposits of considerable economic value. The deposit comprises six horizons: bauxitic clay at the bottom, massive bauxite, massive iron-aluminous crust, iron-aluminous crust dismantled, ferruginous spheroliths and a clay cover equivalent to the "argilas de Belterra" at the top. The sedimentary rocks of the Itapecuru Group are the probable source of the lateritic-bauxite profile and include weathered siltstone and claystone. The mineralogical composition of the three studied units (Itapecuru Group rocks, lateritic-bauxite profile and clay cover) is similar and consist to kaolinite, quartz, hematite, goethite and gibbsite, accessory minerals include anatase and heavy minerals (zircon, tourmaline, rutile, staurolite and opaque). The units differ mainly in this content variation and the absence of gibbsite and goethite in the rocks of Itapecuru Group. The chemical composition of the three units shows that Al2O3, SiO2, Fe2O3, TiO2 and LOI are the most abundant constituents, related to the major minerals. Trace elements content in the three units are heterogeneous with V, Cr, Ga, Zr, Hf and Th showing concentrations above the crustal average, these elements display good correlation with iron oxy-hydroxides. When normalized to chondrites, the three units differ by positive Ce anomaly in the Itapecuru Group rocks, but are similar in negative Eu anomaly, the depletion of LREE and enrichment of HREE. The data obtained show clear affinities between the three units, suggesting that the sediments of the Itapecuru Group are similar to those of the bedrock of lateritic-bauxite profile while their respective cover demonstrates strong relationship with the crusts and spheroliths. The structure of the lateritic-bauxite profile together with mineralogical and chemical data allow to correlate the Rondon do Pará lateritic-bauxite profile with the deposits of Paragominas and Juruti.