Origin and hydrogeochemical evolution of Azarshahr travertine springs, NW Iran

1-Introduction Travertines are limestones that form where hot groundwaters rich in calcium and bicarbonate emerge at springs. Travertines cover a large area southwest of Azarshahr (East Azarbaijan province), in some parts of which active springs are currently settling travertine. One of the main questions about travertine springs is their origin, as well as the secondary processes that have changed their composition along the flow path. To study the origin and geochemical evolution of springs, different ion ratios such as Na/Cl, Br/Cl, I/Cl as well as oxygen isotopic composition and deuterium isotope are used. Hydrogeochemical and isotopic data is used to determine the hydrochemical properties, source of soluble materials, source of spring water, type of spring water, mixing of spring water and concentration of heavy metals in the water of travertine and non-travertine springs. 2-Materials and methods In this study, 16 water samples from 9 travertine and 7 non-travertine springs in Azarshahr region have been analyzed to determine the concentration of major ions using ion chromatography. 6 water samples were selected from springs in the region to determine the concentration of heavy metals and stable isotopes of oxygen 18 and deuterium. Electrical conductivity (EC) and pH of the springs was measured in place by using portable device (WP-84 conductivity-salinity EC meter TPS Company, Australia) and AZ8601 pH/mV meter. Saturation index of samples was measured by using PHREEQC software. 3-Results and discussion Hydrochemical studies have shown that in terms of acidity, spring water is in neutral; their EC value is higher than the standard drinking limit and the water type of travertine springs is bicarbonate. Due to the relationship between pH and temperature in travertine springs, with increasing temperature, the pH value also increases, which is normal. But in non-travertine springs with shallow rotation depth and also lower temperature, the range of pH changes is greater. This could be due to the occurrence of mixing between travertine and non-travertine along the depth-to-surface path. These springs have lower temperatures and more carbonate dissolution has occurred, causing the pH to rise further. The results of this study also show that the origin of the main ions in spring water is the dissolution of carbonates and to some extent evaporates. Isotopic studies of the springs indicate the primary origin of the meteoric and also show that the depth of water circulation in the Qizildaq and Taptapan travertine springs is very high and the height of the feeding area is higher than other springs. 4- Conclusion The study of water origin and geochemical evolution of travertine and non-travertine springs in Azarshahr region using hydrogeochemical, isotopic and heavy metal data has led to the following results: 1) In terms of acidity, the water of the studied springs, like other karst and travertine areas, is neutral and the amount of EC in all springs in the region is higher than the standard drinking limit and is salty. The water type of travertine springs is bicarbonate and the water type of non-travertine springs is chloride. 2) The study of the origin of the main ions in the spring water shows a similar trend for the springs, where the dissolution of carbonates and to some extent evaporites (gypsum and halite) are the main factors determining their chemical composition. 3) Carbonate minerals such as calcite and aragonite are in saturation state in all water samples of Azarshahr travertine springs and the water of all studied springs is supersaturated compared to quartz and chalcedony minerals. 4) In the study of compositional diagrams related to the main ions, it was found that the origin of calcium and salinity alone can not be due to the dissolution of carbonates, gypsum and evaporites, and other factors such as cation exchange have also been affected. 5) Isotopic studies of springs in Azarshahr region indicate the meteoric origin of water in these springs. The depth of water rotation in Qizildaq and Taptapan travertine springs is very high and the height of the feeding area is higher than other springs.