River systems are considered as dynamic sediment transport and deposition agents during Quaternary period; they carry dissolved and sediment loads which are produced by weathering of outcrops of geological formations to sedimentary basins. The aim of this study is to investigate geological parameters which affect on the hydrogeochemical properties of Khar-Rud River water, using chemical experiments and statistical methods. The river basin is located in Central Iran structural zone. 35 river water samples (taken from 40 km of the western sector of this river during wet and dry season of  2013-2014 hydrological  year) were analyzed. The obtained data were analyzed by some statistical methods (correlation coefficient, cluster analysis and box plot) using SPSS software. The statistical results indicate calcium sulfate and sodium chloride (originated mainly from  Miocene evaporite deposits) have the highest effect on the salt content of the river water. The role of carbonate rocks with this regard were not significant.
Introduction
Quality of water resources are controlled by solubility and lithology of drainage basins; rivers are important as fresh-water resources and as an agent of ground-water recharge. The river-water quality is changed by chemical properties of the water of its tributaries. Carbonate and evaporate minerals are more important with this regard.
The drainage basin of Khar-Rud river is a part of Namak-lake basin in Cntral Iran. The aim of this research  is to find the origin of the salt content of this river. Therefore, the focus of the research was on the effect of  the basin lithology on the river water quality.
Materials and Method
In order to recognize the sources of the dissolved content of Khar-Rud river water, lithology of the outcrops in the river basin were studied; the emphasis was on layers with evaporate origin. 35 river water samples (taken from 40 km of the western sector of this river during  wet and dry season of  2013-2014 hydrological  year) were analyzed. Physiochemical analysis were performed on these samples. Water samples were taken from 10 cm depth of the water surface (Fig. 1). The physiochemical analysis include: temperature, pH, electrical conductivity, the main anion contents (Cl^-, SO₄^2-, CO₃^2- and HCO3^-), the main cation contents (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and total-dissolved solids (TDS, tables 1 and 2). The obtained data were also analyzed by some statistical methods (correlation coefficient, cluster analysis, CA, and box plot) using SPSS software (version 16 for Windows) and Excel software (2007) (Table 3; figs. 4 and 5).
Results and discussion
Khar-Rud river flows westward along the Khar-Rud fault; the river basin is located in the west part of the Central_Iran Structural Zone, adjacent to the Sanandaj-Sirjan Structural Zone. The outcrops on the west (north) bank include Mesozoic formations (Lar, Shemshak, Delichay formations and Cretaceous limestone) and Qom Formation (Cenosoic). The outcrops on the east bank mainly consists of the Upper-Red Formation (Miocene), most evaporite minerals (halite and gypsum) are found in this formation (Figs. 2 and 3).
The Khar-Rud river has six tributaries (Fig. 1) each of which has a distinct effect on the chemical composition of the river water (Fig. 4). Based on the chemical composition of the waters, these tributaries are classified in three types: 1- sodium-chloride type (i.e, Shur, Dashatak, Qare-Mohammad and Hesar-Valiasr), 2- calcium-sulfate type (Qare-Mohammad and Shur)  and 3- calcium-carbonate type (Nalbandan).  According to the Pearson's correlation coefficients results, TDS has a positive significant relation with SO₄⁺², Ca⁺², Cl^-, Na⁺ and a shows significantly negative relationship with HCO₃^-2 and K⁺; a negative correlation is also observed between TDS and HCO₃^-. This indicates that gypsum and halite are the main dissolved components in the Khar-Rud River water; carbonate minerals are not significant with this regard.
The cluster analysis of data suggests that there are two distinct groups of components, which allows for a tentative assignment of geological sources. The first cluster contains TDS, SO₄^-2, Cl^-, Ca⁺², Mg⁺², Na⁺, electrical conductivity (EC) which might be derived from the evaporate minerals of the Upper Red Fm.). The second cluster containing HCO₃^-2 and K⁺; they might be originated from other geological sources.
 
Conclusion
This research was done in order  to investigate geological parameters which affect on the hydrogeochemical properties of Khar-Rud River (S. Qazvin Province) water. Results show that gypsum and halite are the main dissolved components of the River water. They are mainly originated from the Upper-Red Formation (Miocene).