Investigation of the Source of 238U, 232Th and 40K Radiation of in the Neyshabour Turquoise Mine and its Environmental Impacts

Abstract

Introduction The Neyshabour Turquoise Mine is located at 55 km North West of Neyshabour in latitude of E58◦, 23ꞌꞌ and longitude of N36◦, 23ꞌꞌ. This area is situated at the Cenozoic continental magmatic arc in the north of Sabzevar ophiolite sequence and extends to Binalood Mountains (Spies et al., 1983; Karimpour and Malekzadeh Shafaroudi, 2013). Rock units consist of Eocene intermediate volcanic and intrusive bodies and breccia's which are the country rock of ore deposits in the Firouzeh area (Mohammad Nejad et al., 2011a). The Turquoise Mine was suggested as the first Iron Oxide Cu-Au-U-LREE mineralized system in Iran (Karimpour et al., 2012). The turquoise was formed on the oxidation zone of this deposit. The mining procedure operates as underground mining and mine wastes that were recycled for extraction of turquoise were released in the vicinity of the mine area and the surrounding Madan village. High radiometric anomaly of Uranium and Thorium has been reported in the Firouzeh area (Karimpour and Malekzadeh Shafaroudi, 2013). The aim of this study is to study the gamma radioactivity of 238U, 232Th, and 40K in different parts of this area (tunnels, rock units, mine waste, habitations and water resources) and to determine the origin of gamma radioactivity by gamma spectroscopy implement via portable gamma scintillation system (MCA) with sodium iodide NaI (Tl) detector. Results The total average natural gamma radioactivity in the mine tunnels was measured to be 98.31 cps. The average gamma radioactivity associated with 238U in the tunnels was 5.2 cps. The average gamma radioactivity associated with 232Th (1.4 cps) in all samples from the tunnels is less than 238U. Highest natural gamma radioactivity associated with 40K was measured in the mine tunnels. Trachyte rock units and the Limonitic soils had the maximum natural total gamma radioactivity and andesite unit shows the least values. The high concentration of these elements in limonitic soils was formed by adsorption of radioactive cations by Fe Oxides. The lowest gamma radioactivity was determined in andesite rock units, coarse grain alluvium and coarse grain soils. Mine wastes from the turquoise mine are explored again by villagers and this might cause exposure to additional dose in this way. The average total gamma radioactivity is 75.26 cps in mine wastes. The highest and lowest gamma radioactivity in the mine waste was associated with 40K and 232Th, respectively. There is a high gamma radioactivity in homes that have been made by local raw materials. Average total gamma radioactivity in rural houses is 83.73 cps. The maximum and minimum total gamma radioactivity was associated with 40K and 232Th, respectively. There is high natural gamma radioactivity in mine drainage waters and springs that which occur on marl unit. The mine tunnels had the most gamma radioactivity and stream sediments show the lowest gamma radioactivity in different samples in the area. 238U, 232Th and 40K radio activities have strong positive relationships and they probably have a similar source. 40K has the most gamma radioactivity in this region. Therefore, trachytic rocks are the source of natural gamma radioactivity in the studied area. Based on mineralogical studies on Neyshabour turquoise mine (Mansouri Gandomani et al., 2020), there are no radioactive elements in Turquois mineral. There are not reliable statistics on occupational diseases and cancer among miners because these patients are sent to Mashhad hospitals or migrate from this area. However, the number of people infected by lung disease such as pneumoconiosis and silicosis is growing and many pensioners and old miners are suffering from different forms of cancer such as cancer of digestive and respiratory systems. The average number of victims of cancer in the Madan village (next to the turquoise mine) is more than other habitants in the Neyshabour area. Although development of cancer is related to several factors, but exposure to radioactivity in job conditions, geological features, presence of radiogenic radon gas in water and air of the area, and presence of 238U, 232Th and 40K in geological formations in the region suggest that radioactive emissions could be considered as the key factors contributing to cancer in this region. Discussion The average level of natural total gamma radioactivity associated with 238U, 232Th and 40K in the Neyshabour turquoise mine area was 87.78 cps. Mine tunnels, houses, mine wastes and geological outcrop have the highest natural total gamma radioactivity, respectively. Trachyte rocks unit has the highest natural gamma radioactivity and andesite coarse-grained clastic sediments display the lowest values. 40K has the most total gamma radioactivity in the study area. Trachytic rocks are the source of natural gamma radioactivity in this region. The radioactivity of 238U, 232Th and 40K in geological formations can be considered as a main factor contributing to cancer.

Keywords

• turquoise
• neyshabour
• environmental impacts
• radioactivity