Cuito
This occurrence, information on the form of which has not been found, consists of a nepheline syenite containing what is described as primary calcite (Sousa, 1921).
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)
This occurrence, information on the form of which has not been found, consists of a nepheline syenite containing what is described as primary calcite (Sousa, 1921).
Chianga is some 4 km in diameter, is deeply eroded and displays little relief. It consists principally of tuffs and/or breccias and syenites, but because of heavy alteration Lapido-Loureiro (1973) could not be certain of the identification of the syenites.
Longonjo is a carbonatite intrusion that forms a hill rising some 280 m above the surrounding peneplained Precambrian granite gneiss. The principal area of carbonatite is 3 km across but the outer margins are everywhere obscured by an apron of superficial deposits.
A rock from the area of Dombe Grande, described by Andrade (1957) as a 'basanitoid', comprises serpentized phenocrysts of augite, labradorite and olivine with nepheline and analcime; an analysis is given. Lapido-Loureiro (1967) refers to aegirine-augite and barkevikite also in this rock.
From 16 km along the road from Noqui to Sao Salvador, Holmes (1915) described a riebeckite-aegirine granite marginal to albite granites. A mode, by weight, gave 32% quartz, 48% albite, microcline and perthite, 16% riebeckite, 4% aegirine and accessories including zircon.