Alkaline Rocks and Carbonatites of the World

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Osongombo

stripes

Occurrence number: 
116-00-011
Country: 
Namibia
Location: 
Longitude: 16.02, Latitude: -20.88

This is the smallest of the Damaraland carbonatite complexes, forming a diatreme of irregular outline with an average diameter of about 450 m. It penetrates marbles of the Damara System which contain small intrusions of Salem granite. The diatreme consists mainly of volcanic breccias, with about one third occupied by beforsite with small areas of iron ore. The beforsite is concentrated in a central zone but an apophysis extends westwards into country rock marbles. Beforsite dykes cut the breccias and country rocks and are sometimes crowded with inclusions. The beforsite is formed predominantly of manganiferous ankerite, which is heavily weathered to iron oxides, apatite, as prismatic crystals and a network of tiny grains which sometimes swell out into veins up to 0.3 m thick, and accessory quartz, plagioclase, plentiful pyrochlore, barite and late calcite. The beforsite grades into the breccias the main constituents of which are fragments of fine-grained granite and fenitized granite with subordinate quartzite, mica-rich carbonate rock and an altered basic rock. Locally the granites are fenitized with aegirine-filled fractures and loss of quartz. Analyses of two beforsites, including full REE data, and Sr, Nd and Pb isotope data are in le Roex and Lanyon (1998). A whole rock analysis is given by Verwoerd (1967).

References: 
LE ROEX, A.P. and LANYON, R. 1998. Isotope and trace element geochemistry of Cretaceous Damaraland lamprophyres and carbonatites, northwestern Namibia: evidence for plume-lithosphere interactions. Journal of Petrology, 39: 1117-46.VERWOERD, W.J. 1967. The carbonatites of South Africa and South West Africa. Handbook, Geological Survey of South Africa, 6: 1-452.
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