Cacuvo
A fine-grained rock of feldspar, nepheline, biotite, hornblende, apatite and zircon occurs within gneisses at this locality.
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)
A fine-grained rock of feldspar, nepheline, biotite, hornblende, apatite and zircon occurs within gneisses at this locality.
Canata is a ring structure with a diameter of 10 km. The ring is partly defined by an arcuate group of low hills with a central plain.
This occurrence forms a hill some 2 km in diameter rising 140 m above the plain. The core of the hill is a coarse syenite which becomes finer grained towards the margins.
This occurrence consists of numerous small hills and outcrops spread over an area of approximately 8x6 km, which are separated by recent sediments. Rock types include carbonatites, silicified feldspathic rocks, quartz fenites and breccias of basement granite.
A circular pattern of hills of fenite define a 6 km-diameter ring in the centre of which is a complex of carbonatites of lower relief. The country rocks are poorly exposed Precambrian granites.
Emplaced in Precambrian granite gneisses the Monte Verde complex is elongated northeast-southwest but part of the complex, particularly to the north and west, is obscured by alluvial deposits.
Nepheline syenite has been described from Monte Elonga and consists of 75% alkali feldspar, 11% nepheline, 8% brown hornblende, a little biotite and accessories including augite and aegirine. Rocks described as nepheline monzonite form dykes of which two analyses are available.
Andrade (1954) describes essexite, nepheline monzonite and nepheline syenite from the Balombo centre.
Chanja is located 12 km south of Balombo and forms a mountain rising 1650 m above the plain. The mountain is described as being composed of nepheline syenite, which forms the southern half of a four kilometre diameter ring structure, which is located at the intersection of two faults.
This occurrence consists of three centres: in the north is an elongate body of breccias centred on Mount Chimbumbo several kilometres south of which is a hill on which are several areas of carbonatite, fenite and basement granite that are surrounded by alluvial and other superficial deposits whi