A sugilite-bearing assemblage from the Wolhaarkop breccia, Bruce iron-ore mine, South Africa: evidence for alkali metasomatism and 40Ar-39Ar dating

Moore, J.M., Kuhn, B.K., Mark, D.F. and Tsikos, H. (2011) A sugilite-bearing assemblage from the Wolhaarkop breccia, Bruce iron-ore mine, South Africa: evidence for alkali metasomatism and 40Ar-39Ar dating. European Journal of Mineralogy, 23(4), pp. 661-673. (doi: 10.1127/0935-1221/2011/0023-2117)

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Abstract

An occurrence of the alkali-rich, Fe-Mn silicate sugilite [KNa2(Fe3+, Mn3+, Al)2Li3Si12O30] is reported from the Wolhaarkop manganese-rich chert breccia at the Bruce iron-ore mine, Northern Cape Province, South Africa. The upper portion of the breccia is dominated by braunite, albite, K-feldspar and aegirine, and locally hosts irregular-shaped void-fills (generally <5 cm) consisting of both zoned and unzoned assemblages of alkali-rich mn-silicates. the zoned void-fills are characterised by marginal needles of a mineral with norrishite-like composition [kmn3+2LiSi4O10(O)2] penetrating into a persistent wall zone that comprises tabular serandite [NaMn2Si3O8(OH)], albite, K-feldspar and lesser granular sugilite. The cores of larger vugs are occupied by masses of interlocking armbrusterite [K5Na6Mn3+Mn2+14(Si9O22)4(OH)10.4H2O] and/or fibrous sugilite. Unzoned assemblages contain a similar mineralogy, comprising albite, K-feldspar, quartz, sugilite, norrishite, serandite, armbrusterite and minor witherite, strontia- nite and kentrolite [PbMn2O2(Si2O7)]. Similarities to sugilite-bearing assemblages at the Wessels mine in the Kalahari Manganese Field suggest that a single regional hydrothermal alteration event in the vicinity of the unconformity between the Olifantshoek and Transvaal Supergroups was the probable genetic cause for both occurrences. 40Ar-39Ar dating of fibrous sugilite, however, yields an age of 620.2 ± 3.3 Ma (2σ) that is distinctly younger than the ages reported for the assemblages from the Kalahari Manganese Field.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Mark, Professor Darren
Authors: Moore, J.M., Kuhn, B.K., Mark, D.F., and Tsikos, H.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:European Journal of Mineralogy
ISSN:0935-1221
ISSN (Online):1617-4011

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