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Sulphide droplets-and the Unit 11/12 chromite band, Rhum: a mineralogical study

Published online by Cambridge University Press:  01 May 2009

A. C. Dunham  and
F. C. F. Wilkinson
A. C. Dunham
Affiliation:
Department of Geology, University of Hull, HU6 7RX, U.K.
F. C. F. Wilkinson
Affiliation:
Department of Geology, University of Hull, HU6 7RX, U.K.
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Abstract

A microscopic and electron microprobe investigation has been made of six samples of the allivalite–chromitite–peridotite band at the junction of Units 11 and 12, Eastern Layered Series, Rhum. Analyses are presented of olivine, plagioclase and pyroxene, the plagioclase showing reverse zoning in the chromitite. Sulphide droplets occur within and above the chromitite, and contain pyrrhotite, pentlandite, cubanite, bornite, digenite, chalcocite, native copper and electrum, as well as chromite zoned to magnetite, spinel and ilmenite. The variation from aluminous chromite to chromite in the chromitite is confirmed by analyses of five new traverses. The rocks formed during and just after the time when new magma entered the magma chamber. The variation in the chromite compositions is ascribed mainly to magmatic variation in composition due to the mixing process.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 5 , September 1985 , pp. 539 - 548
Copyright
Copyright © Cambridge University Press 1985

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