Novas contribuições sobre a geologia da região de Itataia (CE)

Abstract

The study area corresponds to a small segment of the Ceará Central Domain of the Northern Borborema Subprovince, situated in the southeast of Santa Quitéria county (Ceará state), Northeastern Brazil. The lithostratigraphy of this area is represented, almost literally, by the ltataia Group which has been defined, from the base to the top, by the Serra do Céu Formation (predominance of garnet-biotite paragneisses, more or less sillimanitic and generally with a low percentage of leucosomes, enclosing scattered lenses of calc-silicatic rocks ou skarns); Laranjeiras Formation (overlapped and gradational the previous one, is constituted of quartzites with or without muscovite and feldspars); Barrigas Formation composed of migmatitic paragneisses similar to the first formation and with a higher frequency of calc-silicatic rocks ou skarns, showing the Alcantil Formation (marbles and calc-silictic rocks) interdigitated. This Alcantil Formation is the most economically relevant for closing large deposits of calciferous marble and uraniferous phosphate minerals.The phosphorus-uraniferous ore, colophane, occurs in massive bodies, hosted in metacarbonates, sometimes with botryoidal habit, besides those occurrences in the form of veins, in stockwork and as colophone disseminated in breccias. Outside the domain of marbles the colophanite is found inserted in the paragneisses of the Barrigas Formation. Structural handling, using surface and subsurface data, reveals a clear conditioning of the ore distribution to the lithologic type (marble + calcissilictica) and fracture / failure systems, mainly those around of EW and NW, with high to sub-vertical dip surfaces. Regionally, the various mineralized bodies show, on the surface, a conditioning to that E-W direction. Colophanite analysis by X-ray diffraction (XRD) recorded coexistence and not now of fluorapatite with hydroxyapatite, presenting the type formed solely by fluorapatite, associated with quartz, with black spots and having U308 in its composition . In another type fluorapatite, associated with calcite, occurs as small lenses embedded in marbles with speleothems. Finally, FRX data from some uraniferous colophanite samples revealed chemical compositions with the presence of oxides of Rb, Mr, Y, Zr, Nb, Mo, Ag and Cd and others where, in addition, they contain oxides of In, Sn and Th. The Ni, Zn and As were only recorded in varieties without uranium oxide.