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Kwekwe, Buchwa, Mwanezi, Hwedza |
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Zimbabwe |
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Fe
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Super Porphyry Cu and Au
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The Kwekwe, Buchwa, Hwedza and Mwanezi supergene enriched banded iron formations and detrital iron deposits and resources are hosted by Archaean greenstone belts within the Zimbabwe craton in central and southern Zimbabwe.
Banded iron formations (BIFs) within Zimbabwe are largely hosted by elogate, deformed Archaean greenstone belts within the 800 km long by 500 km wide Zimbabwe Craton. The craton is composed of Palaeoarchaean (>3.2 Ga averaging around 3.5 Ga) Sebakwean Group gneisses and greenstones and the more extensive Meso- to Neorchaean (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. These greenstone belts are distributed more or less along the north-western margin of the craton and to a lesser degree along its south-eastern margin with a cumulative strike length of more than 1000 km. They are in general intruded by syn to late 2.7 to 2.6 Ga tectonic granitoids.
The main iron occurrences are found within greenstone belts of the Sebakwian and Bulawayan groups. The Sebakwian group is a 3.5 Ga sequence of komatiitic and basaltic volcanics, BIFs and clastic sediments, while the Bulawayan group comprises a much more extensive ~2.7 Ga complex succession of komatiitic and tholeiitic volcanics, becoming more felsic towards the top, with intercalated chemical and clastic sediments, including BIFs.
The more significant BIF developments are found within the:
i). Midlands greenstone belt, approximately 200 km SW of Harare, including the Kwekwe (or Que Que) deposits which supply the nearby Redcliffs steel complex. In 1970, these deposits were estimated to have a hematite resource of approximately 200 Mt @ 56 to 65% Fe, 4 to 12% SiO2 (Abdulla, 1970), with a production rate from the Ripple Creek mine of 0.45 Mt pa in 2000 (Mbendi website).
ii). Belingwe greenstone belt (near Shabani / Zvishavane, 300 km south of Harare, 150 km ESE of Bulawayo), where canga / detrital ore has been worked at Buhwa (Buchwa) to produce a 63 to 66% Fe hematite product, with a resource in 1970 of 134 Mt @ 63% Fe, 4 to 6% SiO2, 0.02% S, 0.03% P (Abdulla, 1970).
iii). Mwanezi (Mwasesi) greenstone belt, where enriched BIF mineralisation has been estimated to contain 15 Mt of high grade ore and a resource of as much as 3.3 Gt @ 40% Fe west of Chivhu, 130 km SSW of Harare (Abdulla, 1970).
iv). Hwedza (Wedza) greenstone belt, which covers a NE elongated area of 21x 5 km, is located 140 km SE of Harare. It is marked by the Hwedza mountains which rise to 300 m above the surrounding countryside and comprises metamorphosed ultramafic rocks and associated metasediments, mainly BIFs and minor micaceous and ferruginous schists. The BIFs cap the ridges and are generally 5 to 350 m, most being more than 60 m, wide. Individual lenses range from 0.2 to 3.3 km in length. Surface sampling returned values of 62 to 68% Fe, 1 to 6% SiO2, 0.1 to 1% Al2O3, 0.2 to 0.55% P. Potential resources to 50 m depth are estimated at 490 Mt (Matanga, 2005?).
Other smaller accumulations of 5 to 40 Mt of 50 to 60% Fe are developed in other greenstone belts within Zimbabwe, e.g., the Mongula and Manyoka deposits near Chiredzi in the Sabi valley on the SE margin of the craton, Yank in the Midlands greenstone belt near Kadoma (75 km north of Kwekwe) and Nyuna in the Buhwa-Mweza greenstone belt near Masvingo (Abdulla, 1970 and other sources).
The most recent source geological information used to prepare this decription was dated: 1986.
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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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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