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Reliance komatiite - Trojan, Shanganai, Epoch, Hunters Road, Damba - Silwane, Empress, Madziwa |
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Zimbabwe |
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Ni Cu
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Super Porphyry Cu and Au
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The widespread Reliance komatiitic event in the late Archaean Bulawayan Supergroup of the Zimbabwe Craton hosts a series of sulphide nickel deposits in komatiite flows, fissure vents and sills. The main deposits, which are spread across the craton over a length of 550 km by a width of 300 km, include the Trojan, Shanganai, Epoch, Hunters Road, Damba - Silwane, Empress and Madziwa groups of deposits in Zimbabwe and the small high grade Phoenix and Selkirk orebodies to the south-west in neighbouring Botswana.
The Zimbabwe Craton is some 800 km long by 500 km wide and comprises early Archaean (>3.2 Ga) Sebakwean Group gneisses and greenstones and the more extensive late Archaean (3.0 to 2.6 Ga) greenstone sequences of the Bulawayan, Belingwean and Shamvian Supergroups and associated intrusive granitoids, all of which have been compexly deformed. The final feature associated with stabilisationis the 2.58 Ga Great Dyke which cuts across the entire craton (see the Great Dyke record).
The Reliance komatiitic event occurred between 2.8 and 2.6 Ga, mainly within the thickest and best preserved of the craton cover sequences, the Bulawayan Supergroup, which in turn rests on a series of older (but post 3.0 Ga) granitoids and greenstones and the early Archaean proto-cratonic rocks.
The Bulawayan Supergroup comprises the lower sulphide bearing 2.8 t 2.7 Ga Koodoovale felsic suite and the Upper, generally conformable succession made up of the sediments of the Manjeri, the komatiites of the Reliance, the basaltic Zeederbergs and the mixed sediments and volcanics of the Cheshire succession of units.
The Reliance komatiite comprises multiple submarine flow fields which overlie the Manjeri Unit sediments, composed of deep water, sulphide rich, carbonaceous basinal sequences to the north and west of the Craton, but grading to sulphide poor platformal sediments in the south and east. High level sub-volcanic feeder sills which pass through pre-Manjeri basement are associated with flow fields to produce more than eight preserved and largely discrete, sill-flow complexes, each of up to 100 km in diameter. The sills may be up to 40 km in diameter and 2000 m thick. They may be composite and overlapping and comprisea thick lower dunite-peridotite and a relatively thin to intermittent upper pyroxenite-gabbro. These appear to be in turn connected to larger mid-crustal magma chambers. Individual flow fields are 33 to 85 km in diameter and may be up to 2500 m thick, composed dominantly of komatiitic basalt.
The main sulphide nickel deposits are related to flow fields in the north and west and occur on lava channel complexes (eg. Trojan, Shangani, Damba-Silwane and Hunters Road, while Epoch is in a fissure vent). Idealisitically, deposits comprise basal massive to matrix to disseminated sulphides, followed by weakly disseminated sulphides.
The following greenstone belts contain deposits as follows:
Filabusi Belt - Epoch and Knocknara deposits, 15 km apart, 80 km ESE of Bulawayo.
Shangani North Belt - Shangani and Marjory deposits, 10 km apart, 75 km NW of Bulawayo.
Bubi East Belt - Fibre, Flow, Damba, Silwane and Damba South deposits, spread over a 10 km interval, 80 km north of Bulawayo.
Gweru NW Belt - Sword / Ingwenya and Broomrigg deposits, 12 km apart, 140 km NE of Bulawayo.
Midlands SE Belt - Woodridge, Glen Arroch and Hunters Road deposits, over a 15 km interval, 180 km NE of Bulawayo.
Belingwe Belt - Bend deposit, 150 km ESE of Bulawayo.
Masvingo West Belt - Masvingo deposits, 200 km east of Bulawayo.
Bindura-Shamva Belt - Trojan, Trojan Hill, Kingston Hill and Tynan deposits, 65 km NNE of Harare and 375 km NE of Bulawayo.
Madziwa Belt - Madziwa deposits, 150 km north of Harare.
Tonnages are relatively small, with grades from 0.6% to 5% Ni in some of the high grade massive sulphide accumulations.
For detail of the Reliance komatiite event and the individual deposits consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2003.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Anderson I G 1986 - The Empress nickel deposit: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 231-236
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Baglow N 1986 - The Epoch nickel deposit, Zimbabwe: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 255-262
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Chimimba L R 1986 - The Madziwa nickel-copper deposits, Zimbabwe: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 237-241
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Chimimba L R, Ncube S M N 1986 - Nickel sulphide mineralization at Trojan Mine, Zimbabwe: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 249-253
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Johnson R S 1986 - The Phoenix and Selkirk nickel-copper sulphide ore deposits, Tati greenstone belt, eastern Botswana: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 243-248
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Killick A M 1986 - The Damba sulphide nickel deposits, Zimbabwe: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 263-273
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Mackie T A, Ferreira C A M, Finnemore S H 1986 - The geology and exploration of the Matapos Dam nickel-copper occurrence, Zimbabwe: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v1 pp 275-279
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Prendergast M D 2003 - The nickeliferous late Archean Reliance Komatiitic Event in the Zimbabwe Craton - magmatic architecture, physical volcanology and ore genesis: in Econ. Geol. v98 pp 865-891
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Prendergast, M.D. and Wilson, A.H., 2015 - The Nickeliferous Archean Madziwa Igneous Complex, Northern Zimbabwe: Petrological Evolution, Magmatic Architecture, and Ore Genesis : in Econ. Geol. v.110 pp. 1295-1312
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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