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Paragenetic Trends of Oxide Minerals in Carbonate-rich Kimberlites, with New Analyses from the Benfontein Sill, South Africa

Jones, A. P. and Wyllie, P. J. (1985) Paragenetic Trends of Oxide Minerals in Carbonate-rich Kimberlites, with New Analyses from the Benfontein Sill, South Africa. Journal of Petrology, 26 (1). pp. 210-222. ISSN 0022-3530. http://resolver.caltech.edu/CaltechAUTHORS:20160223-092535770

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Abstract

The relationship among kimberlites, carbonate-rich bodies associated with them, and the carbonatites associated with alkalis rock complexes are reviewed. Particular attention is paid to the parageneses of oxide minerals in six carbonate-kimberlites: Peuyuk, Tunraq, Wesselton, Liqhobong, De Beers, and Benfontein. New analyses of spinel, limonite, and perovskite from the lower Benfontein Sill, are consistent with previous reports and can be divided into (1) early macrocrysts and cores of grains, and (2) late rims and groundmass grains. The evolution of a carbonate-rich residuum with progressive crystallization appears to be typical of carbonate-rich kimberlite magmas, and is texturally related to the two stages of oxide precipitation in these carbonate-kimberlites. Thus, early Mg-ilmenite and Cr-rich spinel are separated by reaction textures and carbonate from later Mg-Al-titanomagnetite, perovskite, and accessory utile and apatite. The spinels span a large range in composition from Mg-Al-chromite to Mg-Al-titanomagnetite, with an intermediate gap. This simplified paragenetic scheme, and in particular the spinel trend, is repeated in the five other carbonate-kimberlites reviewed. It may be representative of the hypabyssal kimberlites in general, and others where fluidization processes did not completely disrupt the crystallization sequence.


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http://dx.doi.org/10.1093/petrology/26.1.210DOIArticle
http://petrology.oxfordjournals.org/content/26/1/210PublisherArticle
Additional Information:© 1985 Oxford University Press. Received 11 January 1984; in revised form 17 September 1984. This research was supported by the Earth Science Division of the National Science Foundation Grant EAR-8311758. Specimens of the Benfontein Sill were collected by P.J. Wyllie during the First International Kimberlite Conference in South Africa (1973), courtesy of De Beers Consolidated Ltd., and J.B. Hawthorne. We thank D.M. Schulze for the use of unpublished data from the Kentucky kimberlite, D.M. Schulze, R.A. Exley, D. Scatena-Wachel and A.M. Davis for useful discussion and I.M. Steele, R. Draus, and O. Draugh, for technical assistance (University of Chicago).
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NSFEAR-8311758
Record Number:CaltechAUTHORS:20160223-092535770
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160223-092535770
Official Citation:A. P. JONES and P. J. WYLLIE Paragenetic Trends of Oxide Minerals in Carbonate-rich Kimberlites, with New Analyses from the Benfontein Sill, South Africa J. Petrology (1985) 26 (1): 210-222 doi:10.1093/petrology/26.1.210
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64672
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 Feb 2016 17:46
Last Modified:23 Feb 2016 17:46

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