No abstract

Energy-dispersive x-ray fluorescence (EDXRF) spectrometry was used for the analysis of silicate rocks using pressed powder pellets. It is observed that with this low-cost, simple and fast technique, trace elements such as V, Cr, Co, Ni, Cu, Zn, Ga, Pb, Th, Rb, Sr, U, Y, Zr and Nb can be determined along with 10 major oxides of Na, Mg, Al, Si, P, K, Ca, Ti, Mn and Fe with reasonably good accuracy and precision, depending upon the elemental abundance, analyte matrix and analytical conditions. Performance parameters such as minimum detection limit, accuracy and precision were estimated for these elements in silicate rocks under optimized analytical conditions. The technique is useful when a large number of samples are to be routinely analysed with sufficient accuracy and precision. Selection of operating parameters is discussed for the simultaneous analysis of several elements in a group.

This study models geochemical and adjunct geologic data to define provinces that are favorable for radioactive-mineral exploration. A multi-element bed-sediment geochemical survey of streams was carried out in the headwaters region of the Ganga River in northern India. Overall median values for uranium and thorium (3.6 and 13.8 ppm; maxima of 4.8 and 19.0 ppm and minima of 3.1 and 12.3 ppm respectively) exceed average upper crustal abundances (2.8 and 10.7 ppm) for these radioactive elements. Anomalously high values reach up to 8.3 and 30.1 ppm in thrust zone rocks, and 11.4 and 22.5 ppm in porphyroids. At their maxima, these abundances are nearly four-and three-fold (respectively) enriched in comparison to average crustal abundances for these rock types. Deformed, metamorphosed and sheared rocks are characteristic of the main central thrust zone (MCTZ). These intensively mylonitized rocks override and juxtapose porphyritic (PH) and proterozoic metasedimentary rock sequences (PMS) to the south. Granitoid rocks, the major protoliths for mylonites, as well as metamorphosed rocks in the MCT zone are naturally enriched in radioelements; high values associated with sheared and mylonitized zones are coincident with reports of radioelement mineralization and with anomalous radon concentrations in soils. The radioelement abundance as well as REE abundance shows a northward enrichment trend consistent with increasing grade of metamorphism indicating deformation-induced remobilization of these elements. U and Th illustrate good correlation with REEs but not with Zr. This implies that zircon is not a principal carrier of U and Th within the granitoid-dominant thrust zone and that other radioelement-rich secondary minerals are present in considerable amounts. Thus, the relatively flat, less fractionated, HREE trend is also not entirely controlled by zircon. The spatial correlation of geologic boundary zones (faults, sheared zones) with geochemical and with geophysical (Rn) anomalies infers ore mineralization by hydrothermal processes generated during multiple episodes of deformation and thrusting. The geologic setting of the anomalies also suggests that crystalline rocks (MCT Zone) along the nearly 2500 km length of the LesserHimalayan belt, where in the vicinity of thrust and fault zones, have potential for radioelement mineralization. Zones of higher concentrations of radioelements delineated by this study and locations of anomalous radon discharge determined by other investigations may indicate a potential health hazard over the long term. However, the low human population density precludes direct manifestation of health effects attributable to chronic exposure to these radioelements; however, the magnitude of natural concentrations suggests the need for more detailed studies and monitoring.

Energy‐dispersive x‐ray fluorescence (EDXRF) spectrometry was used for the analysis of silicate rocks using pressed powder pellets. It is observed that with this low‐cost, simple and fast technique, trace elements such as V, Cr, Co, Ni, Cu, Zn, Ga, Pb, Th, Rb, Sr, U, Y, Zr and Nb can be determined along with 10 major oxides of Na, Mg, Al, Si, P, K, Ca, Ti, Mn and Fe with reasonably good accuracy and precision, depending upon the elemental abundance, analyte matrix and analytical conditions. Performance parameters such as minimum detection limit, accuracy and precision were estimated for these elements in silicate rocks under optimized analytical conditions. The technique is useful when a large number of samples are to be routinely analysed with sufficient accuracy and precision. Selection of operating parameters is discussed for the simultaneous analysis of several elements in a group. Copyright © 2000 John Wiley & Sons, Ltd.

Survival of Mesorhizobium ciceri (SP(4)) and Azotobacter chroococcum (CBD-15 and M(4)) was tested on chickpea (Cicer arietinum) seeds treated with fungicides bavistin [methyl N-(1H-benzimidazol-2yl) carbamate] and thiram (tetramethyl-thiuram disulfide), whereas survival of phosphate solubilizing bacteria (PSB), Pseudomonas striata (27) and Bacillus polymyxa (H(5)) was examined on two cultivars (Arkel and BV) of pea (Pisum sativum) seeds treated with thiram. Viability of Azotobacter chroococcum (W(5)) was also examined on wheat (Triticum aestivum) seeds treated with bavistin, captan (cis-N-trichloromethyl thio-4 cyclohexane-1, 2-dicarboximide) and thiram under laboratory conditions using standard dilution and the plate count technique. All the tested strains of diazotrophs and PSB showed decline in their viable population on prolonged contact with fungicides. However, PSB showed variation in their viable population even with the cultivar. BV cultivar of pea seeds showed better recovery of viable P. striata (10.75 to 10.61 log no. of viable cells with in 0-24 hrs) in the presence of thiram, whereas the Arkel cultivar of pea resulted in better recovery of viable B. polymyxa. Azotobacter chroococcum (W(5)), a potential strain for wheat, showed better survival in the presence of bavistin, compared to thiram and captan. Higher viable population of Mesorhizobium ciceri (SP(4)) and Azotobacter chroococcum (M(4)) was recovered from chickpea seeds treated with bavistin compared to thiram. However, thiram-treated seeds resulted in a greater number of extractable Azotobacter chroococcum (CBD-15). Under field conditions, adverse effect of thiram was reflected on the performance of Mesorhizobium ciceri (SP(4)) and A. chroococcum (M(4)) strains, resulting in reduced root and shoot biomass and grain yield, compared to bavistin treated and culture inoculated treatment. CBD-15 showed better performance in the presence of thiram compared to bavistin.