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

Abstract

The aim of this study is to investigate the effect of different rock units and the role of hydrothermal fluids on increasing the concentration 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. Hydrochemical studies show that groundwater resources of the study area are mainly Ca-HCO3 and Na-HCO3 in type and they contain very high concentration of some elements in their chemical composition than normal waters, so that the concentration of As and B in some samples reaches 6320 µg/l and 644 mg/l, respectively. Studies show that metamorphic rocks of the region (including schists, amphibolites, and especially tourmaline-bearing gneisses) due to the release of boron element from their tourmaline and mica minerals have had an effect on 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 the 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 has led to the extensive contamination in the hot springs and surface waters of the region, can be related to their separation from the magmatic and hydrothermal systems.



Introduction

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 south-eastern region of Selmas 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 and especially from springs in the area. Field surveys as well as previous studies (Asadpour et al., 2014 and Yazdi et al., 2018) 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, therefore, study the quality of underground water resources and investigate the interaction of water and rock in increasing the concentration of some elements in the composition of the underground water resources of the region (and especially the very high amounts of toxic elements such as arsenic and boron in the Isti-Su hot spring) and also Investigating the role of hydrothermal solutions related to young igneous intrusive masses seems to be essential.



Materials and Methods

The studied area is located in West Azarbaijan province, about 20 km south-east of Selmas city and 55 km north of Urmia city, and it is considered a part of the catchment area of Urmia lake.

In this study, in order to investigate the characteristics of springs in the region, as well as to investigate the condition of surface water and the effect of stone units on their quality, from the number of 5 samples of springs (including the springs of Sharif Abad village, Isti-So hot spring, Zindasht, Kani Sefid, Shurgol), 1 sample from a well (Bardian village well) and 2 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.



Results and Discussion



The dominant source of water in samples Q1 (spring in Sharif Abad village), Q3 (waterway west of Abgarm village), Q4 (spring in Zindasht village), Q5 (spring in Aghblag village), Q6 (spring in Shurgol village), and Q7 (well in Bardian village) ) were influenced by carbonate rock units. Investigations show that in all the cold water samples of the region (Sharif Abad, Zindasht, Aghblag, Shurgol and Bardian) the dominant anion is HCO3 and the dominant cation is Ca, while in Isti-su hot spring The dominant anion is HCO3 and the dominant cation is Na. The results of calculating the saturation index for minerals show that the saturation index for calcite is between -0.26 to 1.36, aragonite -0.40 to 1.21, dolomite -0.66 to 2.27, gypsum -1.95 to -2.59, anhydrite -2.47 to - 2.89 and halite also changes between -4.12 and -9.01. 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 was not high (Tables 1 and 2) 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

Hydrogeochemical investigations show that the high HCO3 and Ca is 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. Due to the presence of hot magmatic masses in the depths, there is a very high potential for the entry of some elements into the water sources in the Isti-So hot spring area. So that the high concentration of some indicator elements such as As, W, B and Cl can be related to their separation from the magmatic and hydrothermal system, which leads to widespread pollution in hot waters and The area is superficial.