Alkaline Rocks and Carbonatites of the World

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Ninakri

stripes

Occurrence number: 
080-00-002
Country: 
Italy
Location: 
Longitude: -5.77, Latitude: 8.2

The Ninakri complex is intruded into Precambrian schists and comprises two centres 1.5 km apart. The northern centre is composed dominantly of aegirine and aegirine-riebeckite syenite with minor micromonzonite. The southern intrusion is more varied including as it does an arcuate intrusion of micromonzonite and two bodies of nepheline syenite (Morel and Alinat, 1993). Both intrusions reveal major fault displacements. The aegirine syenite consists of microcline perthite, which forms phenocrysts up to a centimetre across and generally bordered by albite, abundant aegirine, biotite, hornblende and accessories with quartz present in some rocks. The aegirine-riebeckite syenite is similar but it contains a little riebeckite intergrown with melanite and less biotite. The nepheline syenite is a leucocratic, fluidal rock with aligned phenocrysts of microcline perthite set in finer grained albite. Interstitial nepheline is plentiful as is biotite and garnet; fluorite is also present but aegirine and amphibole are absent. The monzonite is a fine- to very fine-grained rock of microcline perthite, less albite, abundant quartz, aegirine, sodic amphibole and biotite. Ten rock analyses, including a full range of REE, are given by Morel and Alinat (1993). A detailed study of the mineralogy, including numerous mineral analyses, together with analyses of rocks, with some REE and other trace element data, will be found in a thesis by Yobou (1993).

Age: 
Rb-Sr on biotite gave 1938(40 Ma (Bonhomme, 1962).
References: 
ARNOULD, M. 1961. Étude géologique des migmatites et des granites Précambriens du nord-est de la Cote d'Ivoire et de la Haute-Volta Méridionele. Mémoires du Bureau de Recherches Géologiques et Minières, 3: 1-174.BONHOMME, M. 1962. Contribution a l’étude géochronologique de la plate-forme de l’Ouest Africain. Annales de la Faculté des Sciences de l’Université de Clermont, 5 (Fasc. 5): 1-62.MOREL, B. and ALINAT, M. 1993. Géologie, pétrologie et géochimie des syénites de Ninakri: comparaison avec d’autres massifs syénitiques anorogéniques de Côte d’Ivoire et d’Afrique de l’Ouest. Journal of African Earth Sciences, 17: 213-23.YOBOU, R. 1993. Pétrologie des granitoides du Proterozoique Inferieur du centre-nord de la Cote D’Ivoire (Ferkessedougou-Marabadiassa) évolution magmatique et contexte geodynamique. PhD thesis, Université de Paris-Sud.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith