The effect of lithological units and the role of hydrothermal fluids on the concentration of elements in groundwater resources of the southeast region of Salmas

Introduction
Hydrogeochemical characteristics provide a lot of information about the origin of water, the influence of host rocks, and dominant hydrochemical processes. In areas related to geothermal resources, chemical interactions between hot water (hydrothermal fluids) and surrounding rocks change the composition of water and enrich elements such as V, Co, Ni, Cu, Zn, As, Se, Al, Ag, Cd, Sb, Cs, Ba, W, Au, Tl, and Pb are included in their composition. The presence of hydrothermal sources and different rock units (and especially metamorphism) in the southeastern region of Salmas has caused water sources, especially spring water, to have different chemical compositions. Considering that in the studied area, a major part of water consumption for agriculture and sometimes for drinking is provided through underground water sources, especially from springs in the area. Field surveys, as well as previous studies in the region, indicate the contamination of water and soil resources in the region and negative and dangerous consequences on aquatic ecology, the quality of agricultural products, and health. residents of the region. This study aims to investigate the effect of different rock units and the role of hydrothermal fluids on increasing the concentrations of elements in groundwater resources of the southeast region of Salmas. For this purpose, selected groundwater sources were sampled and the effects of lithology and hydrothermal fluids have been investigated based on the results of chemical analysis of the samples.
 
Materials and Methods
The study area is located in West Azerbaijan Province, about 20 km southeast of Salmas City and 55 km north of Urmia City, it is considered a part of the catchment area of Urmia Lake. This study, to investigate the characteristics of springs in the region, as well as investigate the condition of surface water and the effect of rock units on their quality, from the number of five samples of springs (including the springs of Sharif Abad village, Isti-So hot spring, Zindasht, Kani Sefid, Shourgol), one sample from a well (Bardian village well) and two samples from surface water located in springs drainage channels (including a complete breakdown sample from the west channel of Abgarm village and a sample from the channel north of Abgarm village only for boron element), sampling was done in August 2017. The EC, T, and pH parameters were measured by a WTW portable device in the field. For chemical analysis of samples and determination of anions and cations by titration methods (to determine Ca, HCO3, Cl), film photometer (for Na, K elements), spectrophotometry (for SO4) and also calculation based on Other ions (for Mg, TDS) were carried out in the laboratory of the Municipal Water and Wastewater Company of West Azerbaijan Province. Also, the ICP-MS method has been used to determine the concentration of other elements and heavy elements, and this analysis was done in the laboratory of Zarazma Company.
 
Results and Discussion
The dominant source of water in samples Q1, Q3, Q4, Q5, Q6, and Q7 were influenced by carbonate rock units. Hydrochemical studies show that groundwater resources of the study area are mainly Ca-HCO3 and Na-HCO3 in type. The concentration of As and B in some samples reaches 6320 µg l^-1 and 644 mg l^-1, respectively. The result of the study shows that metamorphic rocks of the region due to the release of boron element from their tourmaline and mica minerals have influenced the concentration of boron in the involved water resources. Moreover, in places such as the Istisu hot spring due to the presence of hot magmatic bodies in depths, there is high potential for some elements to enter the water resources. The high concentration of some indicator elements such as As, W, B, and Cl, which have led to extensive contamination in the hot springs and surface waters of the region, can be related to their separation from the magmatic and hydrothermal systems. The results of chemical analysis of collected water samples show that the concentrations and changes of As, Cs, K, Li, Na, Nb, Rb, S, Se, Si, Sr, Ta, Th, and W elements in the water composition of the cold water samples were not high and as a result, we can consider the role and very little potential for the entry of these elements through the rock units of the region, which are mainly metamorphic.
 
Conclusion
The results showed that the predominant type of underground water in the study area is calcium bicarbonate and in the spa spring, it is sodium bicarbonate, and the concentration of some elements such as As, and B is very high compared to normal water and more than the maximum. The recommended permissible amount is in the drinking water standard. Hydrogeochemical investigations show that high HCO3 and Ca are due to the interaction between water-rock and ion exchange, and due to the release of boron from the structure of tourmaline and mica minerals in the composition of schist metamorphic rocks. Amphibolite and especially gneiss, its concentration has increased in the waters of the region. In the spa springs of the region with Na-HCO3 type with high sodium concentration, due to the absence of evaporite rocks, the origin of Na ions cannot be caused only by the influence of the rock units of the region. The high values of elements As, B, Cs, K, Li, Na, Nb, Rb, S, Se, Si, Sr, Ta, Th, and W and the results of investigating the correlation between these elements in the underground water resources of the region and also the concentrations Above mentioned elements in Isti-So hot spring shows that the rock units of the region alone do not have enough potential and ability to create anomalies in the amounts of these elements in underground water sources.