Sources of dissolved REE in mountainous streams draining granitic rocks, Sierras Pampeanas (Cordoba, Argentina)

摘要

Stream waters draining granitic terrains from the highest part (850 to 2200m a.s.l.) of Sierras Pampeanas (Cordoba, Argentina, similar to 32 degrees S, similar to 65 degrees W) were sampled in order to define sources and distribution of dissolved rare earth,elements (REE), and to describe the geochemical processes that govern their mobility. The contribution of the regional granite to the dissolved REE pool in stream water is limited due to the physical conditions predominating in the area (i.e., steep slopes and semiarid climate). Therefore, precipitation is considered a seasonally significant source controlling REE concentration in stream water. Dissolved REE concentrations are inversely correlated with monthly precipitation and rainfall frequency. During the rainy season (i.e., the austral summer) REE concentrations in stream water are lower than during the dry season (i.e., austral winter). Such low concentrations reflect the balance between the REE input from precipitation and their removal by adsorption. In contrast, during the dry season, the longer residence time of water within fractures and colluvium determines an increased REE concentration in the base flow. Lower pH values also contribute to raise REE concentration through desorption from mineral surfaces. (c) 2007 Elsevier Ltd. All rights reserved.