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Highly complex niobium ores at Sokli are associated with weathered carbonatites and related rocks. The complex was emplaced at about 370 Ma. Three broad groups of rock can be defined, depending on the dominant mineralogy: carbonate-dominated rocks, magnetite and apatite-rich rocks and silicate-dominated rocks. An extensive geochemical study of a suite of whole rock samples has been undertaken, coupled with a petrographical and mineral chemical study of the principal Nb-bearing phase, pyrochlore. Using the pyrochlore mineral chemistry from fresh rock samples as a petrogenetic indicator, it is possible to describe the magmatic evolution of the complex in terms of the differentiation of carbonated melts, with the calcite carbonatites representing relatively early cumulates, the dolomite carbonatites late residual liquids, and phoscorite forming throughout this differentiation process., Highly complex niobium ores at Sokli are associated with weathered carbonatites and related rocks. The complex was emplaced at about 370 Ma. Three broad groups of rock can be defined, depending on the dominant mineralogy: carbonate-dominated rocks, magnetite and apatite-rich rocks and silicate-dominated rocks. An extensive geochemical study of a suite of whole rock samples has been undertaken, coupled with a petrographical and mineral chemical study of the principal Nb-bearing phase, pyrochlore. Using the pyrochlore mineral chemistry from fresh rock samples as a petrogenetic indicator, it is possible to describe the magmatic evolution of the complex in terms of the differentiation of carbonated melts, with the calcite carbonatites representing relatively early cumulates, the dolomite carbonatites late residual liquids, and phoscorite forming throughout this differentiation process.

Pyrochlore is the main ore mineral of niobium and is worked mostly from weathered deposits overlying carbonatites. The chemical and textural characteristics of weathered pyrochlore are controlled by four major factors, the most important of which is the composition of the original fresh pyrochlore. Cation exchange and leaching from the A sites occurs in all deposits and is controlled by the mineralogy of the host rock and the degree of weathering. Water and Ba, and/or Sr, Ce, K and Pb exchange for Ca and Na. Fragmentation produces progressively finer-grained pyrochlore with increasing degree of weathering and, in the most highly weathered horizons, the pyrochlore structure breaks down and its constituent elements may be incorporated into sub-micron, amorphous Fe oxide-crandallite mixtures., Pyrochlore is the main ore mineral of niobium and is worked mostly from weathered deposits overlying carbonatites. The chemical and textural characteristics of weathered pyrochlore are controlled by four major factors, the most important of which is the composition of the original fresh pyrochlore. Cation exchange and leaching from the A sites occurs in all deposits and is controlled by the mineralogy of the host rock and the degree of weathering. Water and Ba, and/or Sr, Ce, K and Pb exchange for Ca and Na. Fragmentation produces progressively finer-grained pyrochlore with increasing degree of weathering and, in the most highly weathered horizons, the pyrochlore structure breaks down and its constituent elements may be incorporated into sub-micron, amorphous Fe oxide-crandallite mixtures.

Host range experiments and field sampling in Nigeria produced no evidence that African rice gall midge, Orseolia oryzivora Harris - Gagné, can develop on plants other than Oryza species. Sampling in three outbreak areas during 1994 showed that the insect's annual cycle varied according to the agroecological zone and rice cropping pattern. In the humid forest zone, Orseolia oryzivora persisted through the short dry season on ratoons of cultivated rice Oryza sativa at a rainfed site and on dry season rice crops at an irrigated one. In contrast, at rainfed sites in the moist savannah zone the pest survived the longer dry season on the perennial wild rice O. longistaminata, while ratoons and volunteers of O. sativa provided 'bridges' between the wild host and wet season rice crops. Early in the wet season at rainfed sites, galls of Orseolia oryzivora were not found at high density on wild rice, ratoons or volunteers. The heavy infestations which developed by October resulted primarily from rapid multiplication on rice crops themselves during the wet season. At all 13 sites sampled, the large majority of galls were found on fallow or cropped rice fields, rather than in ditches, bunds or uncultivated wetland, irrespective of the time of year or the hosts involved. From gall dissections, the parasitoids Aprostocetus procerae (Risbec) and Platygaster diplosisae Risbec caused over 30% mortality at some sites by October but generally increased too late to prevent crop damage. Implications of the results for the management of Orseolia oryzivora are discussed

Field sampling of grasses growing in and near rice fields at 12 sites in Nigeria during April/May 1994 recorded the presence of galls on Paspalum scrobiculatumat densities of up to 10.9 galls per m2. These galls were induced by Orseolia bonzii Harris, sp. n., which is described. This species is morphologically close to, but distinct from, the African rice gall midge, Orseolia oryzivora Harris & Gagné, with which it has been confused in earlier studies of that pest species. In host-transfer experiments O. bonzii did not transfer to rice, Oryza sativa. Six hymenopterous parasitoids were reared from galls of O. bonzii and the most abundant of these were Platygaster diplosisae Risbec, Aprostocetus nr. procerae (Risbec) and Neanastatusnr. cinctiventris Girault. Host-transfer experiments with the Platygasterand Aprostocetus species from O. bonzii on Paspalum indicated that the Platygaster may not transfer onto O. oryzivora on rice whereas the Aprostocetus does. The overlap between the parasitoid faunas of the two species of Orseolia is potentially useful as it may be possible to enhance the natural biological control of O. oryzivora by manipulating parasitoid populations on Paspalum