Neoformación de palygorskita, sepiolita y fluorita en un Petrocalcid xérico del NE de la provincia del Chubut

BOUZA, P.; MARIANO SIMÓN,; JOSÉ AGUILAR,; CORTÉS, E.

Rio Cuarto, Córdoba

Congreso; VII Congreso de Mineralogía y Metalogenia (MINMET); 2004

ABSTRACT: NEOFORMATION OF PALYGORSKITE, SEPIOLITE AND FLUORITE IN A XERIC PETROCALCID OF NORTHEASTERN OF CHUBUT PROVINCE      The studies on soil genesis recently carried out in the Northeast of Chubut province (Patagonia) resulted in the identification of palygorskite and sepiolite in a Petrocalcid soil developed on old fluvioglacial deposits (“Rodados Patagónicos”, RP). The aim of this study was to analyze the factors and processes of palygorskite and sepiolite formation. The profile shows a petrocalcic horizon where sepiolite >> palygorskite >> Mg-smectites were identified. Small quantities of fluorite were also identified by XRD, which was corroborated by the ionic activities of Ca2+ and F- in the soil solution. The presence of sepiolite in the petrocalcic horizon soil was confirmed by observations in the SEM. According to the analytical determinations, the fibrous clay mineral would have been formed from dissolution-precipitation processes of Mg-phyllosilicate and from the Mg2+ supplied by the soil solution during the precipitation of low-Mg calcite. The waterlogging and alkaline conditions favourable to the formation of palygorskite are determined by the abrupt textural transition between the fine materials of the superficial horizons and the coarse deposits of RP. The presence of fluorite in the most developed and alkaline calcretes explains the geochemical control of the Ca2+  which starts with the calcite precipitation.   Keywords: sepiolite; palygorskite; fluorite; Petrocalcid; northeastern Patagonia.