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Nickel-rich metasomatism of the lithospheric mantle by pre-kimberlitic alkali-SCl-rich COH fluids

Citation

Giuliani, A and Kamenetsky, VS and Kendrick, MA and Phillips, D and Goemann, K, Nickel-rich metasomatism of the lithospheric mantle by pre-kimberlitic alkali-S-Cl-rich C-O-H fluids, Contributions to Mineralogy and Petrology, 165, (1) pp. 155-171. ISSN 0010-7999 (2013) [Refereed Article]

Copyright Statement

Copyright 2012 Springer-Verlag

DOI: doi:10.1007/s00410-012-0801-1

Abstract

Metasomatism of the lithospheric mantle sometimes produces unusual assemblages containing native metals and alloys, which provide important insight into metasomatic processes in the mantle. In this study, we describe the metasomatic enrichment of a refractory harzburgite xenolith in Ni, Fe and, to a lesser extent, Cu, Co, As and Sb. The xenolith (XM1/422) derives from the Bultfontein kimberlite (Kimberley, South Africa) and hosts Ni mineralisation that includes native nickel (Ni84.5-98.0), heazlewoodite (Ni3S2) and Ni-rich silicates (e.g. up to 37.5 wt % NiO in olivine, and 22.4 wt % NiO in phlogopite). The presence of several mineral phases enriched in alkali and volatile species (e.g. phlogopite, phosphates, carbonates, chlorides, djerfisherite) indicates that the transition metal cations were likely introduced during metasomatism by alkali-rich COH fluids or alkali-carbonate melts. It is postulated that sulphide breakdown and fluid reaction with refractory mantle rocks contributed to the fluids enrichment in Ni and other metallic cations. The Ni-rich assemblages of xenolith XM1/422 show local chemical disequilibrium, and modelling of the Ni diffusion profiles adjacent to olivine-native nickel and olivine-heazlewoodite grain boundaries, suggests a close temporal relationship between Ni-rich metasomatism and subsequent entrainment by the kimberlite magma. However, metal-rich metasomatism has also been observed in other lithospheric mantle domains, including orogenic peridotitic massifs and the suboceanic mantle; regions unaffected by kimberlite magmatsim. As micro-scale occurrences of metallic phases are easily overlooked, it is possible that metal-rich metasomatism is more widespread in the Earths mantle than previously recognised.

Item Details

Item Type:Refereed Article
Keywords:Native nickel, Olivine, Metasomatism, COH fluids, Lithospheric mantle, Kimberlite
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
Author:Goemann, K (Dr Karsten Goemann)
ID Code:80001
Year Published:2013
Web of Science® Times Cited:10
Deposited By:Central Science Laboratory
Deposited On:2012-10-16
Last Modified:2014-03-28
Downloads:0

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