Source, distribution patterns and resources potential of selenium in soil of north Pakistan: Revealed by a national-scale geochemical mapping

During national scale geochemical mapping in Pakistan, 69 elements including selenium were analyzed in 2563 stream sediment samples, which filled the gap of selenium distribution in the middle section of Tethyan metallogenic belt. The sampling density was 1–2 sites /100 km². The geochemical concentration of selenium in the samples range from 0.008 to 6.849 mg/kg with an average value of 0.306 mg/kg. The highest average concentration of Se was found in the Suleiman Fold and Thrust Belt (anomaly III3), whereas the lowest is in WKLT Kohistan-Ladakh Island Arc. The type of soil in Pakistan with the highest Se concentration is entisol. The high selenium anomalies are delineated in the northeast of Quetta, near Muslim Bagh, in Mekhtar-Musa Khel area and its southwest region, north of Quetta and Khushab. Three strong selenium anomalies have also been identified in the northeast of Islamabad, northwest of Rawalpindi and the east of Dargai, respectively. It is suggested that selenium anomalies, having a correlation with elements of Mo, CaO, S, Sr, are mainly caused by geological background of shale, coal and coal-bearing formations. Negative anomalies are mainly distributed in the northern Pakistan, which is mostly consists of bedrocks with no or very thin layer of soil. The product of anomaly intensity and variance are defined as prospecting favorable degree (Pfd). The product of Pfd and area (S) are defined as Quantity of Mineral (Qm). There are two anomalies with the highest Pfd in the east of Quetta city, and the anomaly in the southwest of Kundian ranks third. The selenium anomalies indicate the areas of potential Se enrichment and supply basic data and information for geochemical investigation on a larger scale or selenium relevant research.