Lutala (Serra Da Neve)

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). Lutala and Nejoio lie on a northwesterly trend which intersects a dominant alignment in Tchivira (No. 29) and is parallel to a dyke swarm in the region. The predominant rock type of the central and southeastern parts of the complex is a nepheline syenite with phenocrysts of alkali feldspar, arfvedsonite and zoned aegirine and aegirine-augite set in a matrix including alkali feldspar, nepheline, analcime, biotite, fluorite and possible eudialyte and lavenite (Pereira and Moreira, 1977). The syenites, which are concentrated at the northwestern end of the complex, generally contain biotite. The map in Pereira and Moreira (1977) also indicates the presence of alkali granite at the northwestern end of the complex but no petrographic details are given. Along the northwestern margin is a strip of nordmarkite which extends to the hill of Babaque the core of which is formed of trachyte lavas that are surrounded by syenite. The trachytes comprise sanidine, albite, biotite and aegirine-augite and the syenites contain an amphibole of the eckermannite-arfvedsonite series. Elsewhere around the complex are remnants of extrusive rocks indicating the generally ‘high level’ of this complex. There is an extensive fenite aureole around all but the northern margins of the intrusion, this reaching a width of four kilometres to the south. The fenites display cataclastic structures and are enriched in biotite, amphibole and sodic pyroxene. There is a dense dyke swarm around the complex which includes dolerite, lamprophyres, fourchite, tinguaite, phonolite, trachyte, rhyolite and porphyritic granites containing aegirine and sodic amphiboles.