A. Keshav Krishna

Assessment of heavy metal contamination in soils around chromite mining areas, Nuggihalli, Karnataka, India

Toxic heavy metals represent one of the possible environmental hazards from mine lands, which affect many countries having historic mining industries. The primary aim of the study was to investigate the degree of soil pollution occurring near chromite mines, and make a systematic evaluation of soil contamination based on geoaccumulation index, enrichment factor and pollution index. This paper presents the pollution load of toxic heavy metals (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sr, V, Zn and Zr) in 57 soil samples collected around three different active (Tagdur), abandoned (Jambur) chromite mining sites as well residential zone around Chikkondanahalli of the Nuggihalli Schist Belt, Karnataka, India. Soil samples were analyzed for heavy metals by using Wavelength dispersive X-ray fluorescence spectrometry. Results indicated that elevated concentrations of Cr, Ni and Co in soils of the study area exceed the Soil Quality Guideline limits (SQGL). The high enrichment factor for Cr, Ni Co obtained in the soil samples show that there is a steady increase of toxic heavy metals risk in this area, which could be correlated with the past mining activity and post abandoned mining in the area. The data was also treated to study the geoaccumulation index, pollution index and spatial distribution of toxic elements. Emphasis need to be put on control measures of pollution and remediation techniques in the study area.

Geochemistry of sedimentary rocks from Permian–Triassic boundary sections of Tethys Himalaya: implications for paleo-weathering, provenance, and tectonic setting

The geochemical characteristics of two sections—the Permian–Triassic boundary (PTB) Guryul Ravine section, Kashmir Valley, Jammu and Kashmir, India; and the Attargoo section, Spiti Valley, Himachal Pradesh, India—have been studied in the context of provenance, paleo-weathering, and plate tectonic setting. These sections represent the siliciclastic sedimentary sequence from the Tethys Himalaya. The PTB siliciclastic sedimentary sequence in these regions primarily consists of sandstones and shales with variable thickness. Present studied sandstones and shales of both sections had chemical index of alteration values between 65 and 74; such values reveal low-to-moderate degree of chemical weathering. The chemical index of weathering in studied samples ranged from 71 to 94, suggesting a minor K-metasomatism effect on these samples. Plagioclase index of alteration in studied sections ranged from 68 to 92, indicating a moderate degree of weathering of plagioclase feldspars. The provenance discriminant function diagram suggests that the detritus involved in the formation of present studied siliciclastic sedimentary rocks fall in quartzose sedimentary and felsic igneous provenances. These sediments were deposited in a passive continental margin plate tectonic setting according to their location on a Si2O versus K2O/Na2O tectonic setting diagram.

Assessment of Groundwater Quality and Identification of Hydrogeochemical Process in Hard Rock Terrain

Environmental geochemical studies are carried out to assess the groundwater quality and identification of hydrogeochemical process in hard rock terrain of Bhongir watershed nearer to the Greater Hyderabad. A total of thirty-eight groundwater samples were collected and analysed for important physicochemical parameters, anions and cations. The analytical data of alkalis (Na+ and K+) and alkaline earths (Ca2+ and Mg2+), reveal that high concentration of Na+ than others (Na > Ca > Mg > K) is probability due to the loss of Ca2+ and Mg2+ and gain of Na+ by the cation exchange process. Among the anions, bicarbonate is identified in majority of the samples in the following order HCO3 > Cl > SO4 which confirms that all carbonate minerals might have been dissolved and leached to the groundwater system. Most of the samples (81%) are exceeding the WHO allowable limits of electrical conductivity for drinking. The data sets further suggest that the water chemistry in the study area is not homogeneous and influenced by complex contamination sources and geochemical processes. Besides, highest concentration of nitrate (565.7 mg/L), sulphate (414 mg/L) and chloride (1444 mg/L) firmly suggests the impact of agricultural activities such as irrigation return flow, fertilizer application on water chemistry. The elevated concentrations of fluoride (i.e. maximum 4.1 mg/L) in most of the water samples (66%) reveal the origin and geochemical mechanisms, i.e. rock–water interaction is driving its enrichment. As majority of the parameters are above the permissible limit, the groundwater is not potable for drinking.

Structures, petrography and geochemistry of Deccan basalts at Anantagiri hills, Andhra Pradesh

The Deccan basalts of Anantagiri hills near Vikarabad are characterized by the occurrence of a complete and continuous sequence of colonnade structures below the laterites. These structures have enabled division of flow units 2, 3, 4, 5, 6 from the bottom upwards, into three well defined zones — Lower Colonnade Zone (LCZ); Middle Entablature Zone (MEZ) and Upper Colonnade Zone (UCZ) underlying a 5–10 m thick laterite cover. These fine to medium grained basalts composed of plagioclase, clinopyroxene, ± olivine, Ti-magnetite, ilmenite, glass, cholorophaeite and zeolites commonly show intersertal, glomeroporphyritic and rare sub-ophitic and porphyritic textures. On the A-F-M ternary plot these basalts plot in the iron rich tholeiitic field. REE plots of these rocks define patterns with mild LREE enrichment and negative Eu anomaly. Their primitive mantle normalized multi-element patterns show mild positive LREE coupled with slight LILE depletion, positive Ba, Ta and Pb peaks. The TiO2/Yb vs Nb/Yb ratios in these tholeiites suggest a slightly enriched source with an MORB affinity. The major and trace element signatures of these tholeiitic basalts occurring at Anantagiri hills and the adjacent low lying areas in south-eastern Deccan Volcanic Province, have broad affinities with the basalts of Ambenali Formation with an overlap on basalts of Poladpur Formation, though with minor variations suggesting geochemical similarity with these two type area basalt formations.