Observations on the relationship between the Plat Reef and its hanging wall

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doi: 10.1179/037174505X62875
Authors:Holwell, D. A.; Armitage, P. E. B.; McDonald, Iain
Author Affiliations:Primary:
Cardiff University, School of Earth, Ocean and Planetary Sciences, Cardiff, United Kingdom
Other:
University of Greenwich, United Kingdom
Volume Title:Mineralization in the northern Bushveld Complex, South Africa
Volume Authors:McDonald, Iain, editor
Source:Mineralization in the northern Bushveld Complex, South Africa, edited by Iain McDonald. Transactions - Institution of Mining and Metallurgy. Section B: Applied Earth Science, 114(4), p.199-207. Publisher: Institution of Mining and Metallurgy, London, United Kingdom. ISSN: 0371-7453
Publication Date:2005
Note:In English. 26 refs.; illus., incl. geol. sketch map
Summary:Observations on the nature of the contact between the Platreef and its hangingwall have revealed that not only were the hangingwall gabbronorites intruded after the Platreef igneous rocks and the development of platinum group element (PGE) mineralisation, but that there appears to have been a significant time-break separating the two intrusive events. The hangingwall gabbronorites truncate several features present within the Platreef pyroxenites but not in the hangingwall, such as shear zones and reef which has undergone alteration by Fe-rich fluids, implying that these features were formed prior to intrusion of the gabbronorites. A fine-grained leuconorite at the base of the hangingwall exhibits textures showing erosion of Platreef orthopyroxene by fine-grained cumulus plagioclase, suggesting intrusion of a hot magma over cooled Platreef. Xenoliths of reef pyroxenite are also found in the hangingwall. PGE mineralisation is present within basal zones of the hangingwall where the hangingwall overlies mineralised Platreef pyroxenite. We interpret the contact as a magmatic unconformity and, as the gabbronorites do not appear to be PGE-depleted, suggest that PGEs and S were scavenged or assimilated from the reef by the intruding magma, producing zones of orthomagmatic PGE mineralisation in topographic depressions at the base of the crystallising hangingwall. The presence of calc-silicate xenoliths in the hangingwall gabbronorites can be explained by footwall anticlines or diapirism which the relatively thin Platreef had not overtopped, allowing footwall dolomite to be exposed to the main influx of hangingwall magma. The identification of a time-break between Platreef and hangingwall intrusion, and the most likely source of basal hangingwall PGE mineralisation being the underlying Platreef, shows that the magma that formed the gabbronorites could not have been the source of PGE for the Platreef as previously thought.
Sections:Economic minerals and ore deposits; Petrology
Subsections:Metallic deposits: specific
Subjects:Alteration; Basement; Gabbros; Hanging wall; Igneous rocks; Inclusions; Intrusions; Layered intrusions; Lithostratigraphy; Magmas; Metal ores; Metallogeny; Microscope methods; Mineral deposits, genesis; Mineral exploration; Mining geology; Models; Palladium ores; Petrography; Platinum ores; Plutonic rocks; Precambrian; Pretoria Group; Proterozoic; Pyroxenite; Textures; Ultramafics; Upper Precambrian; Xenoliths; Africa; Bushveld Complex; South Africa; Southern Africa; Chuniespoort Group; Mokopane South Africa; Plat Reef
Coordinates:S241500 S240000 E0290500 E0285500
Abstract Numbers:06M/433
Record ID:2006037456
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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