The distribution of platinum group elements in the Insizwa Lobe, Mount Ayliff Complex, South Africa; implications for Ni-Cu-PGE sulfide exploration in the Karoo igneous province

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doi: 10.2113/gsecongeo.97.6.1293
Authors:Maier, W. D.; Marsh, J. S.; Barnes, Sarah-Jane; Dodd, D. C.
Author Affiliations:Primary:
Rhodes University, Department of Geology, Grahamstown, South Africa
Other:
Université du Québec à Chicoutimi, Canada
Falconbridge Ventures of Africa, South Africa
Volume Title:Economic Geology and the Bulletin of the Society of Economic Geologists
Source:Economic Geology and the Bulletin of the Society of Economic Geologists, 97(6), p.1293-1306. Publisher: Economic Geology Publishing Company, Lancaster, PA, United States. ISSN: 0361-0128
Publication Date:2002
Note:In English. 38 refs.; illus., incl. 5 tables, sketch maps
Summary:The Mount Ayliff Complex of the Eastern Cape province of South Africa is a layered intrusion of some 800 km2 surface area and up to 1,200 m thickness. On the basis of compositional similarities and spatial association, it is generally interpreted to form part of the Karoo igneous province. Similarities between the Mount Ayliff Complex and the staging chambers and feeder conduits to flood basalts that host magmatic sulfide ores elsewhere in the world suggest that the Mount Ayliff Complex may have an enhanced potential for Noril'sk-Talnakh-type massive Ni-Cu sulfide ores, an idea that is supported by the well-known sulfide occurrence at Waterfall Gorge. Here, we present major-, trace-, and noble-element data for 30 samples of cumulate rocks from a continuous 1,200 m drill core through the Insizwa lobe of the complex, as well as six samples of a footwall sill, the Taylor's Koppie dike, that was considered a possible feeder zone to the lobe, and through a massive sulfide lens in the footwall of the lobe at Ndzongiseni. We show that most of the Insizwa cumulate rocks contain small amounts of cumulus sulfides. The sulfides, including those at Waterfall Gorge, can be explained by a model in which the sulfides were segregated from magma having chilled-margin composition. On the basis of the composition of the chilled margins, the Insizwa magma contained no entrained sulfides and was depleted in platinum group elements (PGE), although not in Cu and Ni, before emplacement. These compositional characteristics are also observed in lavas of the central Karoo igneous province and suggest only limited sulfide segregation from these magmas at depth. Our findings thus indicate relatively little potential for economic magmatic Ni-Cu-PGE sulfide deposits in the Insizwa lobe.
Sections:Economic minerals and ore deposits
Subsections:General
Subjects:Chemical composition; Composition; Copper ores; Emplacement; Intrusions; Magma chambers; Magmas; Major elements; Metal ores; Metals; Nickel ores; Platinum group; Platinum ores; Sampling; Sills; Spatial distribution; Spectra; Thickness; Trace elements; X-ray fluorescence spectra; Zoning; Africa; Eastern Cape Province South Africa; Karoo Basin; South Africa; Southern Africa; Insizwa Lobe; Mount Ayliff Deposit
Abstract Numbers:03M/2539
Record ID:2003005674
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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