• ARDESHIR HEZARKHANI

      Articles written in Journal of Earth System Science

    • Introducing 3D U-statistic method for separating anomaly from background in exploration geochemical data with associated software development

      Seyyed Saeed Ghannadpour Ardeshir Hezarkhani

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      The U-statistic method is one of the most important structural methods to separate the anomaly from the background. It considers the location of samples and carries out the statistical analysis of the data without judging from a geochemical point of view and tries to separate subpopulations and determine anomalous areas. In the present study, to use U-statistic method in three-dimensional (3D) condition, U-statistic is applied on the grade of two ideal test examples, by considering sample Z values (elevation). So far, this is the first time that this method has been applied on a 3D condition. To evaluate the performance of 3D U-statistic method and in order to compare U-statistic with one non-structural method, the method of threshold assessment based on median and standard deviation (MSD method) is applied on the twoexample tests. Results show that the samples indicated by U-statistic method as anomalous are more regular and involve less dispersion than those indicated by the MSD method. So that, according to the location of anomalous samples, denser areas of them can be determined as promising zones. Moreover,results show that at a threshold of U = 0, the total error of misclassification for U-statistic method is much smaller than the total error of criteria of x + n × s. Finally, 3D model of two test examples for separating anomaly from background using 3D U-statistic method is provided. The source code for a software program, which was developed in the MATLAB programming language in order to perform the calculations of the 3D U-spatial statistic method, is additionally provided. This software is compatible with all the geochemical varieties and can be used in similar exploration projects.

    • Hydrogeochemical characteristics and water quality of Aji-Chay river, eastern catchment of Lake Urmia, Iran

      MORTEZA SAFARI ARDESHIR HEZARKHANI SEYYED REZA MASHHADI

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      The Aji-Chay river is the most important river discharging into endangered Lake Urmia in NW of Iran. The present study investigates the hydrogeochemical characteristics and origin of dissolved ions in the Aji-Chay river and some of its tributaries passing through Tabriz plain which is located at the east side of Lake Urmia. For this purpose, 317 water samples were collected during 9 years (2005–2014) from four stations and clustered to nine groups using K-means algorithm. Major cations and anions were considered to distinguish the hydrogeochemical evolution of water. The Piper, Langelier–Ludwig and Stiff diagrams classified water samples into predominant Na–Cl endmember and Ca–HCO$_{3}$ only in the upstream zone. With respect to Gibbs diagrams, mineral saturation indices and geology of the area, water chemistry of the Aji-Chay river reflects that water–rock chemical interactions including dissolution/precipitation of carbonate and sulfate minerals known as dedolomitization and dissolution of evaporitic salts along the flow path are the dominant factors controlling the water chemistry; furthermore, evaporation, silicate weathering, and ion exchange reactions change the chemistry of water to some extent. Overall, water quality is evaluated as poor. Furthermore, intense halite dissolution increases Na concentration in water which in turn reduces its suitability for irrigation purposes.

      $\bf{Highlights}$

      $\bullet$Hydrogeochemical characteristics of main branches of Aji-Chay river are examined through a long-term (9 years) sampling program; then, K-means algorithm is used to cluster the data into 9 groups

      $\bullet$Mineral saturation indices based on the concentration of ionic components in the water were calculated using PHREEQC software at the same thermodynamic conditions of gathered samples

      $\bullet$Several Indices and standard diagrams are utilized to delineate hydrochemical processes that dominate surface water and assess the influence of possible water-rock interactions on water chemistry

      $\bullet$Dissolution/precipitation of carbonate and NaCl-bearing lithological units substantially influence the quality of water

      $\bullet$The suitability of water is characterized as “poor” for irrigation purposes because of high Na concentration and salinity except in the upstream where lithology has not reduced the water quality

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