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Prehnite from the Kalahari manganese field, South Africa, and its possible implications

B. Cairncross, H. Tsikos and C. Harris
Prehnite from the Kalahari manganese field, South Africa, and its possible implications
South African Journal of Geology (December 2000) 103 (3-4): 231-236

Abstract

Prehnite is described herein from the N'Chwaning II mine, Kalahari manganese field for the first time. The habit and composition are atypical for the species. The mineral occurs as elongated, prismatic orthorhombic yellow-orange crystals arranged in sprays and/or aggregates. It is associated with hydroxyapophyllite, datolite, ferroan inesite, calcite and pectolite. SEM, microprobe and XRF analyses reveal typical chemical compositions in terms of SiO (sub 2) , Al (sub 2) O (sub 3) and CaO values, but the mineral has very low FeO and Na (sub 2) O contents, and MnO (+ or -0.4 wt%) is an order of magnitude higher than published values for prehnite. Stable (H and O) isotope data for structurally-bound H (sub 2) O are consistent with a meteoric origin for the precipitating fluid. The existence of prehnite in the Kalahari manganese field provides evidence in support of low-temperature (150-250 degrees C) formation of the mineral and possible metamorphism in the north-westernmost portion of the field, but its importance in terms of processes involving metal upgrading in the Kalahari manganese ores is uncertain.


ISSN: 1012-0750
EISSN: 1996-8590
Coden: TGSAA3
Serial Title: South African Journal of Geology
Serial Volume: 103
Serial Issue: 3-4
Title: Prehnite from the Kalahari manganese field, South Africa, and its possible implications
Affiliation: Rand Afrikaans University, Department of Geology, Gauteng, South Africa
Pages: 231-236
Published: 200012
Text Language: English
Publisher: Bureau for Scientific Publications, Pretoria, South Africa
References: 28
Accession Number: 2002-025503
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
S27°00'00" - S27°00'00", E22°30'00" - E22°30'00"
Secondary Affiliation: University of Cape Town, ZAF, South Africa
Country of Publication: South Africa
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200210
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