MINERALOGICAL AND GEOCHEMICAL CHARACTERIZATION OF PALYGORSKITE FROM GABASA (NE SPAIN) - EVIDENCE OF A DETRITAL PRECURSOR

A mineralogical and geochemical study of the Gabasa outcrop (Huesca, N E Spain) was undertaken. It consists of Early Oligocene marly and clay ey fluvial and lacustrine (playa-lake) sediments. The phases detected were quartz, amorphous silica, calcite, dolomite, pnlygorskite, illite , interstratified illite-smectite, Al-smectite and Mg-smectite. The pa lygorskite expands with ethylene-glycol. Statistical analysis of the g eochemical data shows that the rare earth elements and transition trac e elements are basically associated with the detrital phyllosilicates, although a considerable amount of the latter is contained in the paly gorskite (Sigma REE = 60-70 ppm, Cr+Co+Ni+V+Zn+Cu = 120-150 ppm), in c ontrast to the normally low values for neoformed minerals. This fact, together with the significant presence of Al and Fe in the palygorskit e, suggest genesis involving alteration by dissolution of the 2:1 stru cture of the illite and/or Al-smectite, followed by re-ordering in a f ibrous structure.