ABSTRACT

Three basic minerals, biotite, chlorite and amphibole, were mineralogically and chemically examined to specify primary host phase(s) of As in the aquifer sediments and verify the formation mechanism of As contaminated groundwater of Sonargaon, Bangladesh, where the highest As contaminated groundwater appears in actively recharging zones. Among those minerals, only the chlorite included As by μ-XRF analysis. Fe-rich and tritoctahedral nature indicated this chlorite termed chamosite. The chlorite was weathered to form goethite on the cleavage, however, the goethite did not host the As. Combining with the saturation of goethite in the groundwater (Itai et al., 2008), in situ chemical weathering of the chlorite promoted by accelerated aerobic water infiltration is suggested to be the first stage of formation of the As contaminated groundwater of the Holocene aquifer. This study implies the importance of aerobic aquifer condition to promote the As release via decomposition of As-bearing detrital mineral(s) as the formation mechanism of As contaminated groundwater in the Ganges-Bramaptra-Meghna river basin.