Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 34.9, Latitude: -13.45

The 9x2 km Meponda occurrence is elliptical in shape and has been deformed which is expressed as an intense sub-horizontal foliation and a north-south lineation; the margins are mylonitized. Two rock suites occur: syenites and nepheline syenites. The syenites are predominant and three groups have been mapped (Lulin et al., 1985) the most abundant of which are leucocratic, with a leucocratic to mesocratic group rather less abundant; the third group constitutes albite syenites which are mineralised with high tenors of Nb, Ta, U and REE. All the syenites are coarse rocks of microcline, perthite and albite, with in some facies abundant sodic pyroxene and/or amphibole. They also contain biotite, zircon and magnetite with some rhodonite, apatite, titanite, carbonate and fluorite. The nepheline syenites are disposed as numerous narrow, north-south-trending bands and consist mainly of microcline, albite, nepheline and variable amounts of sodic pyroxene; accessories are similar to those of the syenites together with allanite and pyrochlore. Within the albite syenites are small, lenticular bodies of sodic amphibole pyroxenite and pyroxenite and these rocks, together with the albite syenites, are mineralised, as expressed in the minerals pyrochlore, columbite, zircon, allanite, chevkinite, monazite, fergusonite and britholite. Analyses of the REE, U, Th, Ta, Nb, Zr and Hf in these minerals are available in Lulin et al. (1985) as are some chemical data on rocks; geophysical and radiometric data obtained during prospecting are also given in this paper. Tabular zircon from the syenites has been described by Cesbron et al. (1985).

A U-Pb age of 538 Ma was interpreted as the age of a regional deformation, while a Rb-Sr ‘errorochron’ gave 755(115 Ma. These dates together with structural and metamorphic considerations led Lulin et al. (1985) to suggest that Meponda was probably emplaced between 900 and 1100 Ma.
CESBRON, F., LULIN, J.-M. and PARFENOFF, A. 1985. Un type de zircon exceptionnel: le zircon tabulaire {001} du complexe alcalin de Meponda (Mozambique); signification génétique. Bulletin de Minéralogie, 108: 825-8.LULIN, J.-M., JOURDE, G., MESTRAUD, J.-L. and MROZ, J.-P. 1985. Un nouveau gîte à Nb, Ta, (U, T.R.) en Afrique orientale: le complexe alcalin de Meponda (République populaire du Mozambique.). Chronique de la Recherche Minière, 480: 35-48.
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