Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Hossere Tchegui


Occurrence number: 
Longitude: 13.35, Latitude: 8.45

An approximately circular, 4 km diameter intrusion, Hossere Tchegui forms a hill which is composed predominantly of peralkaline syenites, that are cut by a small intrusion and dykes of trachyte. Gabbro forms an arcuate intrusion in the northwest. The Precambrian schists into which the intrusion is emplaced are thermally metamorphosed. The syenites comprise an outer ring which is cut by later syenites, the former having been mapped as 'white' and the latter as 'brown' syenites (Lasserre, 1978). The syenites contain quartz, alkali feldspar, aegirine, which is zoned with deeper green cores, riebeckite, biotite, fluorite, calcite and apatite.

A Rb-Sr isochron on whole rocks and biotite gave 43±6 Ma (Lasserre, 1978), and five determinations on syenite and trachyte by Cantagrel et al. (1978) ranged from 33 to 37 Ma.

CANTAGREL, J.-M., JAMOND, C. and LASSERE, M. 1978. Le magmatisme alcalin de la ligne du Cameroun au Tertiaire inférieur: données géochronologiques K/Ar. Bulletin de la Société Géologique de France Compte Rendu Sommaire des Seances, 20: 300-3.LASSERRE, M. 1978. Mise au point sur les granitoides dits "ultimes" du Cameroun: gisement, pétrographie et géochronologie. Bulletin du Bureau de Recherches Géologiques et Minières. Paris, IV: 143-59.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith