Sodic metasomatism in the Palaeoproterozoic Hotazel iron-formation, Transvaal Supergroup, South Africa: implications for fluid–rock interaction in the Kalahari manganese field

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.     

COMPONENTS OF CHANGE IN THE SPATIAL DISTRIBUTION OF THE ELDERLY POPULATION IN ONTARIO, 1976–1986

Although the elderly population is increasing rapidly in all parts of Canada, the pattern of change is far from uniform. A number of properties of the aging process are strongly differentiated at the county and township levels, variations which have considerable significance for the design and implementation of social service and health care systems. Using data from the 1976, 1981, and 1986 Censuses for Ontario, components of change in the elderly population are obtained by cohort survival methods. The significance of rapid metropolitan growth of the elderly compared with the slow growth of the rural elderly is highlighted, while intra-county distributional shifts in the elderly population raise important questions for the next decade.
Quoique l'âge de la population augmente rapidement à travers le Canada, ce changement nes'opèrepas de façon uniforme. Certaines caractéristiques du processus de vieillissement sont vraiment differentes à l'échelle des comtés et des municipalités. Ces différences sont d'une grande importance lors de la création etde l'implantation des services-santé et des services sociaux. À l'aide des statistiques de recensement pour les années 1976, 1981, et 1986 pour l'Ontario, les facteurs de changement des populations de personnes âgées sont obtenus au moyen des paramètres de 'survie des groupes.' La signification du taux d'accroissement rapide des personnes â gés en milieu urbain comparé au taux d'accroissement plus lent de ces mêmes personnes en milieu rural est mise en évidence. Les variations de la distribution de cette population d'un comtéà I'autre soulèvent d'importantes interrogations pour la prochaine décade .     

The haves and have nots in Australia's Tropical North – New Perspectives on a Persisting Problem

There is significant confluence in the literature that leads one to expect groups of haves and groups of have nots in socio‐economic systems within common spatial contexts. Several economic theories suggest economic activity to be concentrated in a few core areas with geographically large ‘peripheries’ relying on one or two industries for employment and income. In the context of the north of Australia, issues of disparities in socio‐economic status between the region and elsewhere in Australia, and also within the region have been highlighted in the literature for some time. This paper discusses the contemporary situation using customised data collected and analysed for 55 river‐basin catchments in the Tropical Rivers region of northern Australia to highlight the extent of the haves and have nots problem. A range of spatial economic theories are discussed as theoretical bases for the present day situation and as pointers to revisionist approaches which may address it. Transforming the have nots to improved states of well‐being will be a costly and difficult process. Consequently, we argue that factors other than raw incomes and economic production should be reconsidered and re‐prioritised by governments as redress to the ongoing ‘problem’ of the North.     

Mineralogy and fluid inclusion gas chemistry of production well mineral scale deposits at the Dixie Valley geothermal field,USA

At the Dixie Valley geothermal field, Nevada, USA, fluid boiling triggered the precipitation of carbonate scale minerals in concentric bands around tubing inserted into production well 28–33. When the tubing was removed, this mineral scale was sampled at 44 depth intervals between the wellhead and 1227 m depth. These samples provide a unique opportunity to evaluate the effects of fluid boiling on the scale mineralogy and geochemistry of the vapor and liquid phase. In this study, the mineralogy of the scale deposits and the composition of the fluid inclusion gases trapped in the mineral scales were analyzed. The scale consists mainly of calcite from 670–1112 m depth and aragonite from 1125 to 1227 m depth, with traces of quartz and Mg‐smectite. Mineral textures, including hopper growth, twinning, and fibrous growth in the aragonite and banded deposits of fine grained calcite crystals, are the result of progressive boiling. The fluid inclusion noncondensable gas was dominated by CO₂. However, significant variations in He relative to N₂ and Ar provide evidence that the geothermal reservoir consists of mixed source deeply circulating reservoir water and shallow, air saturated meteoric water. Gas analyses for many inclusions also showed higher CH₄ and H₂ relative to CO₂ than measured in gas sampled from this well, other production wells, and fumaroles. These inclusions are interpreted to have trapped CH₄‐ and H₂‐enriched gas resulting from early stages of boiling.