The chromites of the Bushveld Complex in the Nietverdiend area

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doi: 10.2113/gsecongeo.80.4.896
Authors:Engelbrecht, Johann P.
Author Affiliations:Primary:
Univ. Pretoria, Dep. Geol., Pretoria, South Africa
Volume Title:special issue devoted to the Bushveld Complex
Volume Authors:Von Gruenewaldt, Gerhard, editor; Sharpe, Martin R.; Hatton, Christopher J.
Source:Economic Geology and the Bulletin of the Society of Economic Geologists, 80(4), p.896-910; Symposium on the Bushveld Complex, Pretoria, South Africa, Oct. 31-Nov. 2, 1983, edited by Gerhard Von Gruenewaldt, Martin R. Sharpe and Christopher J. Hatton. Publisher: Economic Geology Publishing Company, Lancaster, PA, United States. ISSN: 0361-0128
Publication Date:1985
Note:In English. 15 refs.; illus. incl. 8 tables, strat. cols., geol. sketch map
Summary:A geologic map and stratigraphic column of the Nietverdiend basin are presented, based on recent mapping and two boreholes drilled in the area. The floor of this part of the Bushveld Complex is undulous with two approximately north-south-trending structures composed of metasedimentary rocks flanking the lower and critical zones; the floor is confined to a north-south-aligned, kidney-shaped basin. The marginal zone is composed of gabbroic and noritic rocks showing erratic variability in mafic mineral composition and reversed zoning in the plagioclases. The lower and critical zones consist of bronzitites alternating with olivine- and/or chromite-bearing rock types. Throughout these two zones the compositions of the silicates remain approximately constant. The chemistry of the LG-1 to LG-4 chromitite layers was investigated in detail and the nature of the cation substitutions assessed. There is an increase in Cr2O3 abundance from layer LG-1 to LG-4 with Al2O3 and/or Fe2O3 being substituted in the spinel structure. Principal component analysis is used to group and differentiate among the four chromitite layers. A dissimilarity between the chemistry of the chromitite layers from the southern and northern sectors of the basin is illustrated. Extensive assimilation of floor rocks by the Bushveld magma, especially during the earlier part of the intrusion is postulated. [G.J.N.]
Subjects:Chemical composition; Chromite; Chromite ores; Chromitite; Composition; Cores; Economic geology; Igneous rocks; Intrusions; Layered intrusions; Metal ores; Oxides; Plutonic rocks; Statistical analysis; Ultramafics; Africa; Bushveld Complex; South Africa; Southern Africa; Transvaal region; Nietverdiend region; Transvaal South Africa
Coordinates:S251500 S245500 E0262500 E0261000
Abstract Numbers:86M/0978
Record ID:1985071667
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists
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