No description available.

Note: / This work has been undertaken beacuse os the fascinating mixed-religious social set up it offers in the town, the model it is likely to serve to the Nigerian community in this aspect of co-existence of religions. Even though all the three strong religious beliefes existing in the country - traditional, Muslim and Christian - have strong footing and long standing in this town, yet religion has been reduced to a secondary position on the social activities of the people; so much so that there is hardly any family which is exclusively Muslim or Christian or traditional. [...]

No description available.

The giant Pascua Au-Ag-Cu high-sulphidation system is located in the El Indio belt in north-central Chile, and is hosted mainly by Triassic granitic rocks and locally by Miocene breccia bodies. Hydrothermal activity involved two distinct high-sulphidation alteration stages, the later of which was accompanied by main stage mineralization. The early hydrothermal activity consisted of extensive and pervasive advanced argillic alteration, local development of vuggy silica and distal argillic to propylitic alteration. This alteration was locally overprinted by an intermediate stage comprising argillic alteration, silicification and primary jarosite, more or less contemporaneously with the formation of Brecha Central, the main breccia body in the deposit. The superimposed second major hydrothermal event produced significant advanced argillic and vuggy silica alteration. The latter likely formed at pH near 0 owing to the limited buffering capacity of previously altered rocks. Termination of the second stage of alteration coincided with the main Au-Ag-Cu mineralizing event, in which Au dissolved in pyrite and enargite, formed inclusions in these minerals, and precipitated as isolated grains of native gold. Detailed EPMA and SIMS imaging and analyses of pyrite and enargite show that both contain Au, Ag, As, Cu, Se and Te and that their distribution is crystallographically controlled. The main trace element associations in the mineralized pyrite are As-Ag, Au-Cu and Se-Te. I suggest that the first two, As-Ag and Au-Cu, were the result of coupled substitution in the Fe site, whereas Te and Se replace S by direct anion exchange. The nature of the coupled substitutions observed in the gold-bearing pyrite underlines the fact that gold is not necessarily coupled with arsenic as previously thought and that arsenic can behave as a metal in the structure of pyrite. Approximately 55% of the gold in the deposit was scavenged from mineralizing fluids that were mainly under-saturated with respect to native gold and trapped into the structure of pyrite and enargite (50 and 5%, respectively). The remaining 45%, including - 7% as inclusions in sulphides, precipitated mainly in the form of native gold with lesser calaverite for which the gold depositional mechanism is interpreted to be an increase in pH that destabilized AuHS and AuCb". Substantial late-stage Ag-enrichment, characterized by halogen-bearing phases, is evident in the upper parts of the deposit and overprints previous alteration and mineralization. The silver enrichment event is interpreted to represent the waning stage of the hydrothermal system. Secondary leaching and weathering of pyrite, enargite and alunite created two supergene products, one dominated by secondary soluble sulphates such as voltaite, massive coquimbite, chalcanthite, and romerite, and one by jarosite. Abundant sulphides in vuggy silica altered rocks, which lacked the capacity to neutralize later oxidizing fluids, were the main locus of formation of the soluble sulphates. Elsewhere, the pH likely rose above 1, which inhibited precipitation of soluble sulphates and favoured formation of jarosite. Direct-ion SIMS images and trace element analyses of soluble sulphates indicate that these minerals likely contain gold in their structures.

A major question in ecology is 'why are tropical forests so species diverse?' One hypothesis to explain tropical species diversity is the Janzen-Connell hypothesis. This model assumes high levels of host-specific seed and seedling predation and / or pathogen attack when seedlings occur at high density near to the parent tree; seedlings are more likey to survive and reach maturity the further they are away from parents / conspecific adults. Theoretically this should lead to a random distribution of each species in the forest, which in turn will lead to high species diversity. Here I test the Janzen-Connell hypothesis for the first time in a submontane dry forest in Nigeria, West Africa. Specifically I tested whether or not a) leaf herbivory decreases and b) seedling survival increases with distance from parent / conspecific adult trees. These two components were tested separately on naturally occurring seedlings and on experimentally planted seedlings. I also tested whether or not conspecific adult trees showed clumped distributions by testing if conspecific nearest neighbours were observed more often than would be expected by chance alone. Naturally occurring seedlings of three species, Pouteria altissima, Newtonia buchananii and Isolona pleurocarpa showed significantly greater survival at distances away from parent / conspecific adult trees. Two out of a total of three species (Entandrophragma angolense, Deinbollia pinnata and Sterculia pinnata) of experimentally planted seedlings showed increased survival at distances away from conspecific adult trees, but this trend was non-significant. Leaf herbivory decreased with distance from parent / conspecific adult trees for four out of a total of six study species, but all relationships of leaf herbivory with distance for these six species were non-significant. Of two individual species, Anthonotha noldeae and Carapa procera, and two species groups tested for clumping, all had a greater number of conspecific nearest neighbours than would be expected to occur by chance alone, and this was significant for the two species groups. The decreased survival of seedlings under parent / conspecific adult trees is likely to maintain tree species diversity in West African submontane forests as predicted by the Janzen-Connell model. The role of host specific seedling herbivores in reducing recruitment under parent / conspecific adult trees requires further investigation. Although conspecific adults showed some degree of clumping no conclusion was reached as to whether this was evidence for or against the Janzen-Connell model.

Diss. (sammanfattning) Stockholm : Karol.inst., 2001. / Härtill 5 uppsatser.

Revised D.Phil thesis-Oxford University, 1998. / Includes bibliographical references and index.

Thesis (PhD (Economics))--University of Pretoria, 2007. / Abstract in English. Includes bibliographical references. Available on the Internet via the World Wide Web.

Zugl.: Hohenheim, University, Diss., 2006.

Diss. Stockholm : Stockholms universitet, 2007.