Lithological influences on occurrence of high-fluoride groundwater in Nagar Parkar area, Thar Desert, Pakistan.

Factors regulating the occurrence of high fluoride (F(-)) concentrations in groundwater near Nagar Parkar Town, SE corner of Pakistan have been investigated considering lithological influences. F(-) ion concentrations in groundwater range up to 7.85 with mean value of 3.33 mg L(-1). Plots of major elements and their normative mineral composition reflect granitic composition of the rocks in the study area. Modal mineralogical analysis show high perthite, plagioclase feldspars and quartz, while micas, amphiboles and pyroxenes occur in minor quantities. Water-rock interactions, based on dissolved ions of F(-), SiO(2), Na(+), K(+), Mg(2+), Li(+) and Sr(2+) suggest that fluoriferous groundwater originates from granitic rocks, typically from albite, biotite, hornblende and pyroxene and its alteration products such as kaolin and soil. The Log TDS, Na/Na+Ca ratio, Mg/Ca+Mg and Cl/Sigma anions are significant to review the impact of weathering processes which promote the availability of F(-) ions in the groundwater of study area. Principal component analysis (PCA) also renders close association among F(-) ions and other elements in the rocks and groundwater. Studies on F(-) estimation in the granite rock, china clay, soil and sand samples also indicate the presence of high F(-) concentration in these materials and average values have been found to be 1939, 710, 254 and 16 mg kg(-1), respectively.