Geo-genic arsenic contamination in the Kerman Cenozoic Magmatic Arc, Kerman, Iran: Implications for the source identification and regional analysis

Abstract

Kerman Cenozoic Magmatic Arc (KCMA) is located in the southeastern part of the Central Iranian Volcano-Plutonic Copper belt. Arsenic contamination from geo-genic source is one of the most important environmental concerns in this area. The main objective of this study was to determine the role of geothermal related activities in the arsenic contamination. For this purpose, the old and active geological indicators of the geothermal activities were investigated through the quaternary travertine deposits and the present hydrothermal warm springs, respectively. Results showed that arsenic is highly concentrated (ranged mainly from 12,400 to 90,500 mg/kg) in the reddish-brown deposits of the travertine rocks. Arsenic showed geochemical association with Co, Cu, Mo, Sb, Tl, Se, Fe, and Mn in these samples. Yukonite [Ca7Fe3+12 (AsO4)10(OH)2015H2O], a rare Ca ferric arsenate hydrous mineral, was the only As-bearing mineral identified in the reddish-brown deposits of the travertine rocks. Arsenic concentration in the hydrothermal warm springs (<38 °C) ranged from 15,900 to 30,500 μg/L (the dominant form was as H3ASO30). Hydrothermal contaminated waters also were characterized by Na–Cl type and high values of EC (11,400 μs/cm), TDS (8300 mg/L), B (42,700 μg/L), Li (3000 μg/L), Fe (900 μg/L), Sb (82.8 μg/L), and Si (47,000 μg/L) and natural anomalies of Cs, Mn, Mo, Rb, Se, and Tl. The obtained hydro-geochemical results are similar to those reported in the literature for worldwide hydrothermal waters. Although, natural attenuation processes, such as adsorption/co-precipitation or mixing/dilution, reduce most of the arsenic contamination from hydrothermal source, but some urban and rural communities are still depending on the arsenic contaminated waters with arsenic concentrations higher than recommended values for drinking or irrigation, a subject that increases the risk of arsenic-related diseases in some areas of the Kerman province.