Assessment of barite of Lasbela, Balochistan, Pakistan, as drilling mud and environmental impact of associated Pb, As, Hg, Cd and Sr

Barite deposits of the Lasbela District, Balochistan, hosted in the Ferozabad Group (FG) of Jurassic are relatively pure and have BaO value ranging from 40.18 to 60.91 % with minor amounts of Sr, Fe and Ca. The measured average density of the studied samples (4.21 g/cm 3 ) is compatible with the API-13A specification. The quantity of water-soluble alkaline earth metals found is very low (av. 50.76 mg/kg) and safe to be used in the drilling mud. The scanning electron microscope study of some of the selected samples revealed nearly 10 % particles are fine (<6 µm) and have equant, subrounded to rounded shape; however, larger particles (>10 µm) are tabular and low in quantity. The average content of Pb (3418 mg/kg) in the barite samples is relatively high as designated by the API specification (1000 mg/kg), while Hg, As and Cd contents are very low, except in a few samples. The average content of Sr is 1.19 %, indicating hydrothermal origin of the barite deposits of the study area and to some extent it is toxic in biological functions. Some of the samples have elevated amount of SiO 2 (1.83–8.88 %) which may cause risk of silicosis in the persons either involved in milling industry or at well site. The positive loadings of first factor of principal component analysis for Ba and S, and density revealed genetic alliance with MVT/SEDEX mineralization, and negative loadings of Ca, Mg and Fe demonstrate hydrothermal alteration of host rock.