The Influence of Weathering on Hydrogeochemistry of Streams Draining Volcanic Rocks: Bidkhan Stream, Southeast of Bardsir in Kerman

Bidkhan stream drains the caldera of the inactive volcano of Bidkhan which lies at a distance of 40 Km southeast of Bardsir town of Kerman Province. The main purpose of this study was to determine the source of ions and compounds dissolved in this stream water, with specific regard to chemical weathering. Therefore, 12 samples were taken along the route of this stream. EC, pH and temperature were determined in the field and the concentration of ions and compounds were determined using standard laboratory methods. After controling precision and accuracy of the analyses, the Piper diagram, ionic ratios and statistical techniques (multivariate analysis, cluster analysis and correlation matrix) were used to interpret the data. Accordingly, all samples belonged to “temporary hardness” class and were of calcium bicarbonate and magnesium bicarbonate type. Ionic ratios indicate silicate weathering. In factor analysis, Li, Sr, Ba, Ca, Na and Mg cations and bicarbonate, sulphate and chloride anions all groups in factor 1. So, almost all of the cations are released from silicate weathering, chloride from rainwater, bicarbonate from CO2 gas of air and soil and sulphate from rain water and probably pyrite oxidation. Fe, Mn and Al are grouped in factor 2 which means source (mafic silicate weathering). Hence, a common silicate weathering is the main source of major cations and heavy metals. Considering the chemical composition of waters, both mafic and felsic silicates have played a role. This is attested by the lithological diversity of the volcanic rocks of the area