Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Chilwa Province
Longitude: 35.22, Latitude: -15.17

Chinduzi is situated at the western end of the Mongolowe-Chaone-Chikala line of nepheline syenite-syenite intrusions (No. 103-00-027) and is continuous with Mongolowe through a low saddle in which runs the main Zomba-Liwonde road. Although the mass is known as Chinduzi the northern part is called Mberekezi (Bloomfield, 1965a). The intrusion has not been studied in as much detail as the adjacent ones. The low hills of Chinduzi and Mberekezi were mapped by Bloomfield (1965a) as nepheline syenite with faulted areas of pulaskite to the west and a further area of pulaskite extending northeastwards to the western margin of the Mongolowe complex. Along the northern edge of the intrusion there is a zone several hundred metres wide of fenitized gneiss and gneiss also extends around the western and southern margins. Elsewhere the contacts are hidden beneath recent sediments. Basic xenoliths are widespread and thin pegmatitic bands are common. Dykes of foyaite cut the nepheline syenites, notably along the northern margin and Bloomfield (1965a) correlates these with the Junguni intrusion (No. 103-00-025). Most of the Chinduzi rocks are aegirine-biotite-nepheline syenites with katophorite occurring in about one third of the samples studied by Woolley and Jones (1987). Analyses of nepheline, pyroxene, which ranges continuously from salite to aegirine, katophorite and mica are given and discussed by Woolley and Platt (1986). Four whole rock analyses are in Woolley and Jones (1987).

K-Ar dating of biotite in pulaskite gave 116(6 Ma (Cahen and Snelling, 1966) and Eby et al. (1995) obtained fission-track dates from titanite of 133.1(18.5 and 133.5(14.6 Ma.
BLOOMFIELD, K. 1965a. The geology of the Zomba area. Bulletin, Geological Survey of Malawi, 16: 1-193.CAHEN, L. and SNELLING, N.J. 1966. The geochronology of equatorial Africa. North-Holland Publishing Company, Amsterdam. 195 pp.EBY, G.N., RODEN-TICE, M., KRUEGER, H.L., EWING, W., FAXON, E.H. and WOOLLEY, A.R. 1995. Geochronology and cooling history of the northern part of the Chilwa Alkaline Province, Malawi. Journal of African Earth Sciences, 20: 275-88.WOOLLEY, A.R. and PLATT, R.G. 1986. The mineralogy of nepheline syenite complexes from the northern part of the Chilwa province, Malawi. Mineralogical Magazine, 50: 597-610.WOOLLEY, A.R. and JONES, G.C. 1987. The petrochemistry of the northern part of the Chilwa alkaline province, Malawi. In J.G. Fitton and B.G.J. Upton (eds), Alkaline igneous rocks. 335-55. Geological Society of London, Special Publication 30.
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