CLAY MINERALS OF DEVONIAN CLAYSTONES FROM DURAZNO DEPARTMENT. URUGUAY.

Abstract

The clay mineral fraction « 4 ¡.Lm)of selected c!aystones belonging to the Cerrezuelo and the Cordobes Formation, devonian in age, has been studied sistematically in order to determine the day mineralogy and its physicochemical and technological properties. A saprolitizied material overlain by the Cerrezuelo Formation was also aualyzed with the purpose of determining the composition and possible relations to the studied sediments. SampUng was carried out on the pelitic sequences outcropping in Cerrezuelo and Paso Tejera localities, Departamento Durazno, Uruguay, corresponding te: the Geological Sheets Yi, Cerro Chato and Arroyo Cordobés, Iocated in the southern border of the Cuenca de Paraná. All the samples are basically kaolinitic associated, in some cases, with minor amounts of smectites and illite and very small quantities of quartz and feldspars. On rich kaolinite clays the structural ordering was determined founding that they belong to the First Type except one which belongs to the Fourth type. The Crystallinity Index varies from 0.90 to 1.20 which is consistent with tbe slructuraI msorder found through hidrazyne hidrate intercalation reactions. lIomoionization tests carried out Iay aside the presence of cblorite. Smectites present have been identified as montmorillonite and beidellite and Li tests would point out to high charge montmorillonite and Iow charge beidellite. Kaolinite is considered of detritaI origin, derived fram deeply weathered Inigmatic basament rocks, pointing out to deposition on passive margin coasts. Tbe presence of smectites may be due to the argillogenesis of basic bodies in tbe basemenj: rocles (saprolite and Cerrezuelo Formation) and possibly to volcanic provenance. PhYsicochemical and technological stumes carried out show that these materiaIs are excelent for first quality refractories