The Anna's Rust Sheet and related gabbroic intrusions in the Vredefort Dome-Kibaran magmatic event on the Kaapvaal Craton and beyond?

The Anna's Rust Sheet (ARS) and a suite of mineralogically and chemically related intrusions in the core and collar of the Vredefort Dome (in particular, the Vredefort Mafic Complex: VMC) represent a newly recognised type of high Ti gabbro in this central part of the Kaapvaal Craton. This lithology, referred to as the Vredefort Type IV mafic intrusion, is distinguished from chemically similar Type V intrusions (the Karoo dolerites) by the presence of glomeroporphyritic plagioclase and higher Th content and from Type III intrusions (≈ 1600 Ma gabbro) by the lack of cross-cutting pseudotachylitic breccia veinlets. Petrographic features and both major and trace element compositions of all Type IV intrusions are very similar. Based on its Rb-Sr isotope age and character, a gabbroic intrusion from Majuba Colliery (Mpumalanga Province) is also thought to belong to the ARS (Type IV) suite of tholeiitic intrusions. Rb-Sr isotopic analysis resulted in a preferred age of 1052±11 Ma (2ω) for biotite and plagioclase data for ARS, VMC and Majuba samples. The Rb-Sr age for the ARS is further supported by ⁴⁰Ar-³⁹Ar stepheating ages for plagioclase and pyroxene separates from two ARS and VMC samples, which favour formation of this gabbroic intrusion at ca 1000 Ma ago. These results suggest that an ≈ 120 m thick sheet intrusion may be present throughout a major part of the Vredefort Dome. While Kibaran-age (ca 1–1.2 Ga) alkaline, both mafic and felsic, magmatism, as well as tectonic and hydrothermal activity at that time, have been known in the central Kaapvaal Craton, a widespread tholeiitic magmatic component has now been added to this record. There is a strong likelihood that this magmatic event occurred throughout the southern African subcontinent and perhaps into Antarctica.     

Aluminium in Lake Cuicocha,Ecuador, an Andean Crater Lake: Filterable,Gelatinous and Microcrystal Al Occurrence

In Lake Cuicocha watershed, a young caldera lake, soils consist of volcanic deposits with a high SiO₂ and Al₂O₃ content; these andisols are in an early stage of development; and in drainage water from the watershed, aluminium concentrations reach 15.0 μmol L⁻¹. Total aluminium concentrations in Lake Cuicocha water raises up to 7.2 μmol L⁻¹, with nearly 70% occurring as filterable Al at neutral to weak alkaline conditions. Al polymerization to gelatinous aggregates of a few hundred micrometres in diameter as well as the occurrence of Al microcrystals like gibbsite as an ageing product of gelatinous Al polymers was noted in the lake water. The gelatinous Al leads to the formation of larger aggregates resulting in flocs of bacteria, algae, microorganisms and detritus.     

Boron substitution in diopside evaluated through 11B nuclear reaction analysis

 Nuclear reaction analyses on boron in flux-grown Me³⁺- and Na⁺-doped diopside crystals utilising the ¹¹B(p,2α)⁴He reaction in conjunction with EMP analyses for major elements and optical absorption spectroscopy for determination of Me-valence state distributions show that appreciable amounts of B may enter the diopside lattice in crystals produced in Na₂B₄O₇ fluxes. The results indicate that the substitution ^[6]Me^3+[4]B^3+[6]Mg²⁺ ₋₁ ^[4]Si⁴⁺ ₋₁ operates in the present diopside samples in addition to the coupled substitution ^[6]Me^3+[8]Na^+[6]Mg²⁺ ₋₁ ^[8]Ca²⁺ ₋₁. The specific NRA technique applied allows for quantitative, high resolution (ca. 5 μm) B analyses at ppm level as well as high-resolution and high-contrast imaging of B-concentration patterns in minerals. The estimated detection limit and relative error of the B analyses are 10 ppm and 5–10%, respectively. Received: 20 September 1999 / Accepted: 6 June 2000     

Health risk of heavy metals from vegetables irrigated with sewage water in peri-urban of Dera Ismail Khan,Pakistan

Health risks of heavy metals in vegetables irrigated with sewage water were investigated in the present study. The findings indicated a massive accumulation of heavy metals in soil and vegetables collected from Dera Ismail khan, Pakistan. The concentration levels of heavy metal in vegetables grown on soil irrigated with untreated sewage water were significantly higher at (P ≤ 0.001) than in vegetables grown on fresh-water-irrigated soil and proceeded the recommended limits of World health organization. Moreover, the findings also indicated that the adults and children consuming such vegetables ingested a large proportion of the selected toxic metals. Health risk index was greater than one for Pb and Cd in all the selected vegetables and was greater than one for Ni in three vegetables like Spinacia oleracea, Benincasa fistulosa and Lactuca sativa. Health risk assessment would be a useful tool for information regarding any threats of heavy metals contamination in vegetables.     

Hydrous pyrolysis of a Type III source: fractionation effects during primary migration in natural and artificially matured samples

A core from the Cambay Shale Formation of the Cambay Basin, containing immature Type III organic matter, was pyrolysed at 300°C for different durations of time to different maturation levels. Fractionation effects were studied employing a three-step extraction technique after removal of the expelled pyrolysate. The extractable organic matter (EOM) obtained on extraction of the whole core is assumed to be that present in open pores, while that obtained on finely crushing the sample is assumed to be that present in closed pores. The EOM obtained from 1 cm chips is termed EOM from semi-open pores. The gross composition of the pyrolysates expelled during pyrolysis is not similar to the oils reservoired in the area, and there is no significant fractionation observed between expelled pyrolysates and unexpelled EOM. Our study indicates movement of fluids between closed, semi-open and open pores. In both systems, there is a higher concentration of EOM in open pores than in semi-open and closed pores, and the fraction of EOM in open pores is much greater in the artificial system than in the natural system. Fractionation effects on n-alkane and isoprenoid hydrocarbon-based parameters were also studied. n-Alkenes are present in semi-open and closed pores of the immature core and in the core after it was pyrolysed to 300°C for 6 and 48 h, but are absent in the open pores. n-Alkenes are present in closed pores in the naturally matured core. Presence of n-alkenes in the pyrolysates expelled during the 6 and 48 h experiments, but their absence in the open pores of the core, indicates that expulsion also occurs through temporary microfractures during laboratory pyrolysis, whereas in the natural system expulsion from closed pores seems to be only via semi-open and open pores.     

Mechanism of loading on plates due to explosive detonation

This paper investigates the various mechanisms and parameters that are responsible for delivering impulse to a vehicle that is unfortunate enough to detonate a buried mine. Small scale tests are used to examine the effects of air blast or ejected sand in imparting impulse to a plate that is located above the surface of the saturated soil that contains the explosive. Parameters such as confinement, stand off distance, depth of burial of the explosive, density of the soil, and saturation level of the soil are also examined.     

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Gold–Telluride Mineralization in Pb–Zn–Fe Ores of the Aktash Skarn Deposit (Western Karamazar,Tajikistan)

Geology of Ore Deposits - The article describes magnetite–sulfide assemblages of minerals containing native gold and tellurides in the Pb–Zn–Fe ores of the Aktash skarn deposit in...