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Graftonite in phosphatic iron formations associated with the mid-Proterozoic Gamsberg Zn-Pb deposit, Namaqua Province, South Africa

Published online by Cambridge University Press:  05 July 2018

M. Stalder  and
A. Rozendaal
M. Stalder
Affiliation:
Department of Geology, University of Stellenbosch, Chamber of Mines Building, Private Bag X1, Stellenbosch 7600, South Africa
A. Rozendaal*
Affiliation:
Department of Geology, University of Stellenbosch, Chamber of Mines Building, Private Bag X1, Stellenbosch 7600, South Africa
*
*E-mail: [email protected]
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Abstract

Granular aggregates of fine-grained graftonite (Fe,Mn,Ca)3(PO4)2 and intergrown wolfeite (Fe,Mn)2(PO4)(OH) occur in amphibolite-facies metamorphosed iron formations associated with the Gamsberg Zn-Pb deposit, South Africa. To date, these minerals were believed to have limited parageneses, being essentially restricted to granitic pegmatites and iron meteorites. This paper is the first report of the occurrence of graftonite and wolfeite in a regionally metamorphosed, iron formation-hosted setting. The aggregates are found together with Mn- and Pb-rich apatite and calcian pyromorphite in a pristine unit of almost pure chemical precipitates, the origin of which is intimately linked to the base-metal mineralizing process. Evidence from Gamsberg supports previous studies conducted on pegmatite-hosted graftonites that a simple host rock mineralogy and geochemical prerequisites, such as high activities of Fe, Mn, Ca and a deficiency in F, exert a dominant control on the stabilization of these minerals. However, in a marine sedimentary environment, significant concentrations of phosphorus have to be precipitated to prevent stabilization of all the phosphorus as fluorapatite. The paucity of graftonite in such settings suggests that the combination of these requirements is only rarely achieved.

Keywords

graftonitewolfeiteiron formationsGamsberg Zn-Pb depositSouth Africa
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 6 , December 2002 , pp. 915 - 927
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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