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Yimengite of K–Ti metasomatic origin in kimberlitic rocks from Venezuela

Published online by Cambridge University Press:  05 July 2018

Peter H. Nixon  and
Eric Condliffe
Peter H. Nixon
Affiliation:
Department of Earth Sciences, The University, Leeds LS2 9JT, U.K.
Eric Condliffe
Affiliation:
Department of Earth Sciences, The University, Leeds LS2 9JT, U.K.
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Abstract

This second recorded occurrence of yimengite, K(Cr, Ti, Fe, Mg, Al)12O19, is in a Precambrian kimberlitic sill in the Guaniamo District of Bolivar Province, Venezuela. The paragenesis is similar to that of the type area in Shandong Province, China, where the mineral is in kimberlite dykes. At both localities the yimengite is a K, Ti-bearing metasomatic product of chromium-rich spinel. In the Venezuela rocks the spinels are of the type occurring both as diamond inclusions and as a component of diamond-related Cr-rich garnet harzburgite mantle xenoliths. Yimengite contains significant amounts of barium (up to 3.4wt.% BaO) and is thus transitional to the recently described mineral hawthorneite, Ba(Cr, Ti, Fe, Mg)12O19. Both members are part of a suite of titanate minerals found in kimberlites and their inclusions which has been described by Haggerty and coworkers; they formed as a result of mantle metasomatism generated by K- and Ba-rich fluids. In Venezuela, metasomatism of this type would appear to be deeper than that usually recorded, namely in the basal lithosphere. The metasomatizing fluids are derived from the underlying, more oxygenated asthenosphere. The host kimberlitic rocks are not significantly enriched in K and Ba, but these elements are concentrated in later micaceous dykes which are conjectured to have been generated within similar metasomatized mantle.

Keywords

yimengitehawthorneitespinelkimberlitic rocksVenezuela
Type
Non-silicate Mineralogy
Information
Mineralogical Magazine , Volume 53 , Issue 371 , June 1989 , pp. 305 - 309
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1989

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