Nejoio is an oval-shaped complex of 2x1.5 km with an area of fenites up to a kilometre wide extending around the eastern margin; there is little exposure to the west.
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In an extensive memoir illustrated with geological maps and numerous field photographs Lapido-Loureiro (1973) described all the principal carbonatites of Angola, with an earlier, briefer account (Lapido-Loureiro, 1968). Some chemical and mineralogical data on many of these are to be found in Issa et al. (1991) and discussions of their sub-volcanic structures in Lapido-Loureiro (1969). A relatively full list of occurrences of alkaline rocks as well as carbonatites together with brief descriptions of many of them will be found in Lapido-Loureiro (1967). Apart from the monograph of Lapido-Loureiro (1973) on the carbonatites, detailed accounts of the numerous Angolan occurrences are scarce. For the majority of occurrences there are few or no data on the field relationships with only petrographic accounts of one or a few specimens available. In spite of this there are many papers considering the spatial distribution of the Angolan alkaline rocks, noting that they are concentrated in a few provinces and that they define clear lines (e.g. Lapido-Loureiro, 1968). A geochemical study of 29 specimens from six carbonatite complexes is that of Alberti et al. (2000)
Lutale is a large (40x17 km) complex, largely of syenites and nepheline syenites, which together with the nearby intrusions of Chiuerinde and Nejoio (Nos 23 and 24), have been referred to as Serra da Neve (Pereira and Moreira, 1977).
In the Serra da Macula is an occurrence of nepheline-bearing syenite consisting of 76% orthoclase, 2% oligoclase, 0.25% nepheline, 7% biotite, 6% titanaugite, 2% barkevikitic amphibole, 2% olivine, 4% opaque minerals and 1% apatite. A chemical analysis is available (Gonçalves, 1965).
This occurrence comprises tuffs and feldspathoidal syenites. A nepheline-sodalite syenite comprises 49% orthoclase, a little oligoclase, 29% nepheline, 4% sodalite, 13% aegirine-augite, 1% biotite and accessory opaques, titanite, apatite and calcite.
Dykes which occur in the vicinity of Chapeu Armado, one of which forms the summit of Chapeu Armado Hill, are nephelinites (Beetz, 1934).
The hill of Tchivira rises sharply some 1400 m from the surrounding rounded topography, covers more than 100 km2 and has a concentric structure which is discernable on air photographs. There are photographs of the area in Alves (1968). The Bonga carbonatite complex (No.
Located 11 km northeast of Tchivira (No. 29) Bonga forms a steep-sided hill rising 900 m from a peneplain; there is a central depression 200 m deep. It is clearly shown in photographs in Alves (1968). Bonga is a carbonatite plug which cuts Precambrian granites, migmatites and gneisses.
According to a map of Lapido-Loureiro (1973, p. 167) this occurrence comprises an elongate body of carbonatite of 2x0.6 km, but no petrographic details are given.
Lapido-Loureiro (1967) describes this locality as comprising a nepheline syenite with augite, aegirine and amphibole. Gonçalves (1965) refers to a syenite stock.
Virulundo is a nearly circular plug of carbonatite with a diameter of nearly 3 km, with which no consanguineous intrusive silicate rocks are associated. It forms a steep-sided, in places vertical, hill rising to 800 m above it's base.