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Venetia |
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Limpopo (Northern) Province, South Africa |
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Diamonds
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Venetia diamond mine is located on the farm Venetia, 25 km south of the intersection of the international borders of Botswana, Zimbabwe and South Africa, 450 km NNE of Johannesburg and some 80 km from Messina in the Northern Province of South Africa.
The mine was opened in 1991 and commenced production of diamonds in 1992. In 1995, 4.35 million carats (Mct) were mined, or 45% of South African production. It had an annual output of 5.1 Mct from 4.7 Mt of ore in 2002 at a recovered grade of 107.8 carats per hundred tonnes (cpht) of ore making it South Africa's largest diamond mine. The average value of the stones sold in 2000 was USD 55 per carat. Total reserves + resources in 2000 were 117.4 Mt @ 98.6 cpht for 115.7 million carats of diamonds.
Diamond-bearing gravels were first found in the area in 1903, close to the Limpopo River, 35 km north east of the present mine. In 1969, De Beers commenced a reconnaissance sampling program to locate the source of these alluvials and discovered viable kimberlite pipes in 1980.
There are a number of known kimberlites forming the Venetia cluster, comprising at least 14 pipes and one dyke system clustered over an area of approximately 3 sq. km while the total surface area of the kimberlites themselves is 28 ha. Some of the pipes were formed as multiple intrusive events, resulting in a variety of kimberlite types being encountered during mining operations. The two largest pipes, the kimberlites K1 (12.7 ha) and K2 (5 ha), are currently being mined (2004) in a single open pit operation at an average grade of 136.4 cpht.
The main pipe, dated at 519±6 Ma, is irregular and elongate striking east-west with maximum dimensions of 640 x 260 metres, covering 12.7 hectares at surface. It dips at an 82°N and is intruded along the axis of a plunging anticline, following the structure of the country rock.
The country rock comprises gneiss, amphibolite and minor pegmatite of the cratonised Limpopo Mobile Belt close to the transtion to the Kaapvaal craton to the south. The pipe dominantly composed of diatreme facies tuffisitic kimberlite breccia. Three relatively small hypabyssal facies intrusions occur close to the pipe margins. One of these pre-dates, and two post-date the main TKB intrusion. Numerous late stage hypabyssal facies kimberlite dykes are also recognised.
Venetia is a conventional open-pit mine expected to continue past 2020. As the mine becomes deeper, the feasibility of underground operations and of mining other pipes in the cluster will be investigated. The current targeted pit floor level is at a depth of 400m.
The most recent source geological information used to prepare this decription was dated: 2004.
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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Allsopp H L, Smith C B, Seggie A G, Skinner E M H and Colgan E A, 1995 - The emplacement age and geochemical character of the Venetia kimberlite bodies, Limpopo Belt, northern Transvaal: in S. Afr. J. Geol. v98 pp 239-244
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Barton J M and Pretorius W, 1998 - Crustal xenoliths in Venetia kimberlite pipes indicate a decollement at approximately 10 km beneath the central zone of the Limpopo Belt, South Africa: in S. Afr. J. Geol. v101 pp 323-327
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Barton Jr. J M and Gerya T V, 2003 - Mylonitization and decomposition of Garnet: Evidence for rapid deformation and entrainment of Mantle Garnet-Harzburgite by Kimberlite Magma, K1 Pipe, Venetia Mine, South Africa: in S. Afr. J. Geol. v106 pp 231-242
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Barton, Jr. J M, Barnett W P, Barton E S, Barnett M, Doorgapershad A, Twiggs C, Klemd R, Martin J, Mellonig L and Zenglein R, 2003 - The geology of the area surrounding the Venetia kimberlite pipes, Limpopo Belt, South Africa: A complex interplay of nappe tectonics and granitoid magmatism : in S. Afr. J. Geol. v106 pp 109-128
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Burgess, R., Kiviets, G.B. and Harris, J.W., 2004 - Ar-Ar age determinations of eclogitic clinopyroxene and garnet inclusions in diamonds from the Venetia and Orapa kimberlites: in Lithos v.77, pp. 113-124.
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Klemd R, Martin J, Schmidt A and Barton, Jr. J M, 2003 - P-T path constraints from calc-silicate metapelitic rocks east of the Venetia kimberlite pipes, Central Zone, Limpopo Belt, South Africa: Have these rocks seen granulite-facies conditions? : in S. Afr. J. Geol. v106 pp 129-148
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Kurszlaukis S and Barnett W P, 2003 - Volcanological and structural aspects of the Venetia kimberlite cluster – a case study of South African kimberlite maar-diatreme volcanoes: in S. Afr. J. Geol. v106 pp 165-192
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Pretorius W and Barton, Jr. J M, 2003 - Petrology and geochemistry of crustal and upper mantle xenoliths from the Venetia Diamond Mine - evidence for Archean crustal growth and subduction: in S. Afr. J. Geol. v106 pp 213-230
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Pretorius W and Barton, Jr. J M, 2003 - Measured and calculated compressional wave velocities of crustal and upper mantle rocks in the Central Zone of the Limpopo Belt, South Africa – implications for lithospheric structure: in S. Afr. J. Geol. v106 pp 205-212
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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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