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[en] In principle, authigenic gypsum and anhydrite are excellent candidates for dating by the uranium-series decay scheme yet have been neglected because of cumbersome dissolution requirements. We present a simplified and manageable procedure for sample dissolution of sulfate minerals using cation-exchange resin. Calcium sulfate is shown to dissolve readily in the presence of cation-exchange resin in the hydrogen from by exchange of Ca²⁺ for H⁺. Urandium and thorium isotopes associated with the mineral are released from the solid and fixed on the resin during dissolution. The isotopes are then readily eluted for isolation and analysis by standard alpha spectroscopy techniques. (orig.)

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[en] Field experiments on sulphur fertilization in cotton cultivar CIM-I09 were carried out at Central Cotton Research Institute Multan, Pakistan, in silty loam soils. The treatments consisted of four sulphur doses (0, 7, 14, 28 kg ha-l) and two sulphur sources (gypsum and ammonium sulphate). Sulphur fertilization showed significant increase in seed cotton yield, boll number and boll weight. The addition of 7 kg S ha-1 seemed sufficient to overcome deficiency in silty loam soils for optimum cotton production. There were no differences in seed cotton yield due to sulphur sources. The petiole sulphate-sulphur concentration increased with increasing doses of sulphur fertilizer. The concentration of SO/sub 4/-S > 2000 ppm seemed sufficient for normal cotton growth and optimum seed cotton yield. (author)

[en] In this paper I present an example of the research that the Mineral Surface Group of the Munster University is conducting in the field of Crystal Growth. Atomic Force Microscopy (Am) in situ observations of different barite (BaSO4) faces growing from aqueous solutions, in combination with computer simulations of the surface attachment of growth units allows us to test crystal growth models. Our results demonstrate the strong structural control that a crystal can exert on its own growth, revealing also the limitation of the classical crystal growth theories (two dimensional nucleation and spiral growth models) in providing a complete explanation for the growth behaviour at a molecular scale. (Author) 6 refs

[en] Knowledge of oxygen and sulphur isotopic equilibria in the BaSO₄-HSO₄^--H₂O system permits the use of barite as a geothermometer and isotopic indicator. Sulphur isotopic fractionation between HSO₄^- and H₂S previously studied is undetectable (<0.4⁰/₀₀) between BaSO₄ and HSO₄^-. Oxygen isotope fractionation factors (α) for BaSO₄-H₂O in 1m NaCl solution (110 to 350⁰C) reported here are: 1000 lnα(BaSO₄-H₂O) = 2.64(10⁶/T²)-5.3+-0.3 These data can be corrected for ion hydration effects in solution to give the fractionation factors in pure water: 1000 lnα(BaSO₄-H₂O) = 3.01(10⁶/T²)-7.3+-0.1 Applications of the barite geothermometer are summarised; indicated temperatures of formation are less than 170⁰C. Isotopic analyses of barites from the Mississippi Valley-type ore deposits, Derbyshire, U.K., give linear correlations on a delta³⁴S versus delta¹⁸O plot. The slope of the lines is close to that calculated from the experimental equilibrium data, but the system is complicated by isotopic variations with location and the possible contribution from two ore fluids

[en] Polyhalite (K²Ca²Mg(SO⁴).2H²O) is an important mineral present in the bedded evaporites of the WIPP site, southeastern New Mexico. Polyhalite contains two structurally bonded water molecules, and it is thus important to know if this mineral formed at or close to the time of sedimentation or, as proposed by others more or less continuously throughout the Mesozoic and Cenozoic. If formed much later than original evaporite formation, then this implies a new source of water in order for polyhalite to form in turn raising questions about water abundance and mobility in the bedded evaporites. Polyhalite is not well suited for Rb-Sr geochronologic study because of the large amounts of common Sr, but it has been shown to be suitable for study by the K-Ar geochronologic methods. Pure polyhalites and those mixed with very small amounts of impurities yield K-Ar dates in the range of 200 to 220 MYBP and indicate little if any, loss of ₄₀Ar. Polyhalites mixed with sylvite, halite, and (Na,K)Cl yield lower ages due to loss of ₄₀Ar from the halides. Apparent age lowering is proportional to halide content and an extrapolated age of formation of near 225 MYBP results. Collectively, the K-Ar data convincingly show that the polyhalites formed at the time of sedimentation (except for isolated occurrences near dike intrusions) in Late Permian time. Finally, thermodynamic calculations, supported by petrographic study, show that polyhalite is often stable with respect to carnallite, sylvite and other minerals formerly thought to be older than polyhalite. 1 figure, 1 table

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[en] The Brazilian fertilizers phosphate industry uses a raw material de phosphoric acid, obtained by acid attack to phosphate rock, producing 3 million of tones per year of gypsum as a by-product, named phosphogypsum. The use of this material has been stimulated due to its advantages as building materials and a fertilizer for reducing the environmental impact caused by its disposal product in the neighborhood. Since the phosphate rock have have uranium and thorium associated, during the processing, the natural radionuclides are redistributed through products and by-products. Thus, for a wide utilization of phosphogypsum, a radiological characterization is necessary. This paper present some results of uranium, thorium and radium concentrations in phosphogypsum samples, from representative fertilizers national industries. (author). 8 refs., 2 tabs