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Chemistry and origin of the Mayo Kila sapphires, NW region Cameroon (Central Africa): their possible relationship with the Cameroon volcanic line

Citation

Mbih, KP and Meffre, S and Yongue, RF and Kanouo, NG and Jay, T, Chemistry and origin of the Mayo Kila sapphires, NW region Cameroon (Central Africa): their possible relationship with the Cameroon volcanic line, Journal of African Earth Sciences, 118 pp. 263-273. ISSN 1464-343X (2016) [Refereed Article]

Copyright Statement

Copyright 2016 Crown Copyright

DOI: doi:10.1016/j.jafrearsci.2016.03.004

Abstract

Mineralogical, chemical and geochronological studies constrained the origin of sapphires from Mayo Kila, Northwest Cameroon. The sapphires are mostly blue, with sizes ranging from 2 to 5 mm. The pale blue grains are transparent, whereas, other corundums are transparent to translucent and/or opaque. The sapphires are dominantly euhedral to sub-hedral with few polished lustrous grains, acquired features during moderate to short distance transport from a proximal source rock. Solid inclusions are limited to rutile and zircon.

Trace element analysis of sapphires shows significant concentration (in ppm) in some elements: Fe (2208–14,473), Ti (82–1783), Ga (77–512), Mg (0.9–264.9), Cr (b.d.l −168) and V (1.3–82). The other elements (e.g. Sn, Nb, Ta, Th, Zr, Ni, Ce) are generally below 10 ppm. The calculated ratios for some of the selected elements show an extreme variation: Fe/Mg (43–3043), Fe/Ti (2–76), Ti/Mg (1–328), and Ga/Mg (0.4–363). They are dominantly corundum crystallized in alkaline magma (s) with few from metamorphic source (s).

Trace elemental features with Hf (13,354–26,238 ppm), Th (4018–45,584 ppm) and U (7825–17,175 ppm), and Th/U (0.39–2.65) found in zircon inclusions are compatible with quantified values in magmatic crystallized zircons. The Cenozoic age (mean of 30.78 ± 0.28 Ma) obtained for zircon inclusions is close to the age of some igneous rocks found within the Cameroon Volcanic Line (e.g. rocks of the Mount Oku: 31–22 Ma), showing the same period of formation. The most probable source of the zircon host sapphires is the Oku Mountain located SW of Mayo Kila.

Item Details

Item Type:Refereed Article
Keywords:sapphire, geochronology
Research Division:Earth Sciences
Research Group:Geology
Research Field:Geochronology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Meffre, S (Dr Sebastien Meffre)
ID Code:109861
Year Published:2016
Funding Support:Australian Research Council (CE0561595)
Deposited By:CODES ARC
Deposited On:2016-07-05
Last Modified:2017-01-30
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