Geochemistry of Groundwater in Ultrabasic and Peninsular Gneissic Rocks, Salem District, Tamil Nadu

Mineralogic, hydrogeologic and geochemical data of ultrabasic and Peninsular gneissic rocks of Salem covering an areal extent of about 194 km² around Salem magnesite mine area were employed to determine the source of solutes to groundwater and to assess the chemical weathering processes. The results indicate that the flux of dissolved solids from the abandoned mines are controlled by interaction between ultrabasic rocks and materials derived from local bedrock. Mass balance calculations indicate that dissolution of feldspar and ferromagnesian minerals releases Na, Ca and Mg. The average denudation rate was found to vary from 0.3 to 4.2 tons/km²/yr for a discharge of 5.3 × 10⁸1/yr, and from 0.5 to 8 tonnes/km²/yr for a discharge of 10 × 10⁵ 1/yr. Mineral solubility study of Mg-phase in the system shows that serpentine is the dominant Mg²⁺ contributor.