PROSPECÇÃO GEOBOTÂNICA DE URÂNIO E GEOLOGIA A NORDESTE DE CUIABÁ, MATO GROSSO

Resumo

Sediments and fossils of reptiles of Cretaceous age occur on Fazenda Roneador and Fazenda Albernaz wich are respectively 220 and 230 kilometers northeast of Cuiaba in Mato Grosso. The fossils represent radioactivity anomalies as do outcrops of green mudstone wich are intercalated with sandstone of the Bauru Series. Analyses of water from steams and springs in the region revealed a uranium content ranging from 0.18-12.0 parts per billion. Outcrops of green impermeable mudstone present suitable conditions for the development of a plant called "Capim Carona" and classified as Xyris sp., which is characteristic of a humid environment. Chemical analyses of ash from the roots and stems of this plant indicate a uranium content that ranges from 1.90 to 35.98 parts per million for the roots and 0.14 to 4.30 parts per million for the stems. In order to establish the normal uranium content of this plant, a sample was collected from soil overlying the Furnas Sandstone in an area wich had not been mineralized by uranium. The ash from this sample contained 0.17 parts per million uranium in the stems and 2.31 ppm uranium in the roots. Considering the data from this plant as background, the anomalous values from the plants associated with the green mudstones show a radioactivity of 15.5 times the background value for roots and 24 times the background for stems.