Geology of the Yellow Mine (Taita-Taveta District, Kenya) and other yellow tourmaline deposits in East Africa

Simonet, C.

Journal of Gemmology 27(1): 11-29

2000


ISSN/ISBN: 1355-4565
Accession: 019054922

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Abstract
Tourmaline is a common gemstone in Kenya and Tanzania but little information is available on the geology of its deposits. The geology of a major yellow (savannah) and bicolour tourmaline deposit, the Yellow Mine in the Mangare area (southern Kenya) is described. Mg-tourmaline (dravite-uvite series) of yellow and green colour occurs in a pegmatite which has undergone several stages of deformation, metasomatism and metamorphism. For comparison, several other yellow tourmaline deposits from southern Kenya and Tanzania are also briefly described. Yellow tourmaline deposits may be linked to gneisses and anatectic pegmatites, or to the result of the interaction of such pegmatites with different lithologies such as ultrabasic rocks or marbles. An example of coexistence of dravitic and elbaitic tourmaline in a pegmatite from the John Saul Mine (southern Kenya) is also given. New mineralogical and gemmological data on east African tourmalines are also provided. Tourmaline showing a yellow core and a green rim are common in different kinds of geological environments in east Africa; this indicates the existence of a major, wide scale genetic mechanism for such crystals.