A thin radioactive dyke of carbonatite agglomerate occurs 6 km east-southeast of Kapiri Hill (No. 103-00-022), southeast of the village of Kanono (Garson, 1965b, Map 1).
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The group of alkaline intrusions located west and south of Lake Chilwa were first described in detail by Dixey et al. (1937) who referred to them as the Chilwa Series, but later writers (e.g. Garson, 1966) have used the term ‘Chilwa Alkaline Province’. The province is of considerable interest for two main reasons: firstly, it lies at the extreme southern end of the East African Rift system and is the only province along the rift which is essentially intrusive. Secondly, the province is characterised by the great diversity of rocks present ranging from carbonatites, through nephelinites, ijolites and nepheline syenites, to syenites, quartz syenites and granites. The carbonatites were the first to be recognised in Africa and in fact Dixey and Smith (Dixey et al., 1937) described 11 carbonatite centres, the importance of which may be gauged from the fact that only about half-a-dozen carbonatites had been recognised worldwide at that time. Very full reviews of the carbonatites in the province have been published by Garson (1965a and 1966) and a general account of the province emphasising the tectonics and petrochemistry, and taking into account adjacent areas of Mozambique, is that of Woolley and Garson (1970). A further review (Woolley,1991) considers research on the province in terms of progress over recent decades. Geochronological data are compiled in Eby et al. (1995). It should be pointed out that there are numerous intrusions in the adjacent areas of Mozambique that are coeval with those of the Chilwa Alkaline Province: these are described under the entries for that country.
Nsengwa Hill is a steep-sided feature rising some 350 m above the surrounding country the core of which is a plug of microsyenite that has been intruded and altered by a dyke-like body of agglomerate, carbonatite agglomerate and quartz-rich carbonatite.
Junguni forms a horseshoe-shaped hill of nepheline syenite 2.5 km in diameter that is surrounded by recent unconsolidated sediments; there are two small satellite intrusions to the northeast (Bloomfield, 1965a).
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.
The overlapping complexes of Mongolowe, Chaone, Chikala and Chinduzi, the last described separately (No. 103-00-026), are the most extensive centres of nepheline syenite-syenite in the northern part of the Chilwa Province.
The Zomba-Malosa complex is the largest intrusion in the northern part of the Chilwa province. It is pear-shaped in plan and extends southwards for 24 km from the Mongolowe intrusion (No. 103-00-027), with which it is in contact; the maximum width is 13 km.
Mpyupyu is a small conical hill rising from recent sediments fringing the southwestern shores of Lake Chilwa. It consists of hornblende-biotite syenites, some of which contain a little quartz. There are rare pyroxene cores to the amphibole which is in turn mantled by biotite.
Python Island, in the northern part of Lake Chilwa, contains a vent filled with blocks of gneiss and small areas of breccia consisting of angular fragments of slightly fenitized granulite and syenitic gneiss in a sparse comminuted matrix containing siderite and goethite.
The Chilwa Island centre was the first carbonatite to be recognised in Africa (Dixey et al., 1935), Smith appreciating that specimens of limestone sent to him by Dixey were similar to the carbonatites of the Fen complex.
The Tundulu carbonatite complex lies some 3 km southeast of Lake Chilwa and comprises a central area of carbonatite, agglomerate, nepheline syenite and potassic fenite around which extends a broad aureole of fenitized Precambrian basement rocks, containing Karoo dolerite dykes, cut by dykes and