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Petrological and geochemical evidence is presented on the occurrence of aegirine in the Palaeoproterozoic Hotazel iron-formation, which hosts the giant manganese deposits of the Kalahari manganese field, South Africa. The mineral has an essentially pure Na end-member composition and occurs sporadically in iron-formation immediately bordering the manganese ore beds. The development of aegirine appears to have taken place due to the action of late-infiltrating, saline hydrothermal fluids at the expense of a pre-existing, binary quartz–hematite assemblage. It is proposed that such a process would have overprinted (and therefore post-dated) a spatially more extensive, low-temperature alteration event which brought about thorough carbonate leaching, oxidation and residual enrichment of metals in the Hotazel iron–manganese rocks. [ABSTRACT FROM AUTHOR]

Prehnite is described herein from the N'Chwaning II mine, Kalahari manganese field for the first time. The habit and composition are atypical for the species. The mineral occurs as elongated, prismatic orthorhombic yellow-orange crystals arranged in sprays and/or aggregates. It is associated with hydroxyapophyllite, datolite, ferroan inesite, calcite and pectolite. SEM, microprobe and XRF analyses reveal typical chemical compositions in terms of SiO[sub 2], Al[sub 2]O[sub 3], and CaO values, but the mineral has very low FeO and Na[sub 2]O contents, and MnO (+/- 0.4 wt%) is an order of magnitude higher than published values for prehnite. Stable (H and O) isotope data for structurally-bound H[sub 2]O are consistent with a meteoric origin for the precipitating fluid. The existence of prehnite in the Kalahari manganese field provides evidence in support of low-temperature (150-250 Celsius) formation of the mineral and possible metamorphism in the north-westernmost portion of the field, but its importance in terms of processes involving metal upgrading in the Kalahari manganese ores is uncertain. [ABSTRACT FROM AUTHOR]

Studies the metallogenic importance of glacial processes occurring prior to the development of the Kalahari manganese deposits in South Africa. Origin of the Kalahari manganese deposits; Comparisons between the Kalahari manganese deposit and other manganese deposits of volcanogenic origin; Questions on the aspects of the Hotazel iron and manganese association on the Kalahari deposits.

Previous studies on naturally radioactive materials suggested that they can have a mutagenic effect on plants (growing in sands in Kerala, South West India), and on bats (dwelling in an abandoned underground mine of primary monazite ore in Namaqualand, Western Cape, South Africa). We hypothesised, based on previous theoretical work, that radioactive sands would not induce mutants in microorganisms over time scales typical of doubling times in the natural environment. The potential of exceptionally monazite (Th)-rich mineral sands collected from the coast of Espirito Santo, Brazil to induce single-point reversion in Escherichia coli cultures (both repair-competent and repair-deficient strains) was tested using the tryptophan reverse mutation assay. The results show that at least on a short-term scale (1-7 days), the monazite-rich sands did not cause an increase in reversion above background.