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Finsch |
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Northern Cape, 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 Finsch diamond mine is located some 130 kilometres WNW of Kimberley, between Kimberley and Postmasburg in the Northern Cape Province of South Africa (#Location: 28° 23' 5"S, 23° 26' 38"E).
The Finsch pipe, which was discovered in 1960, is the most important kimberlite in a cluster that comprises 3 kimberlite pipes (Finsch, Shone and Bowden) and 3 dyke sets (Botha, Smuts and Bonza). Up until 1995, approximately 93 million carats had been produced at an average grade of 80 cpht, while in 1995 In 1995, a total of 1.72 million carats were produced at an average grade of 49.3 cpht. In 2000 1.925 million carats were produced from 4.204 Mt of ore @ 45.8 cpht at an average value of USD 50 per carat. Reserves + resources in 2000 totalled 105.3 Mt @ 42.7 cpht for 45 million carats of diamonds.
The mine, initially open-cut from 1965, but underground from 1990, is based on the major 118 Ma aged Finsch kimberlite pipe cutting a Palaeoproterozoic sequence from the Ghaap Plateau Dolomite Formation through to the Kuruman member of the Asbestos Hills Ironstone Formation.
The Finsch pipe has a surface area of 17.9 ha with a conical shape decreasing in diameter with depth. It is located on the precursor Smuts dyke set striking at approximately 50°. The pipe is composed of diatreme facies to a depth of 680 metres below surface, with the transition to the hypabyssal facies root zone occurring below the 900 metre level. Internally the pipe is composed of nine different phases of kimberlite, including tuffaceous kimberlite breccia and hypabyssal kimberlite, although no crater facies have been recognised.
Each of the different kimberlite phases has a distinct geology and grade signature. In spite of this geological diversity, the pipe is dominated by only two volumetrically significant intrusions, which together comprise up to 90% or more of the total kimberlite volume. The F1 intrusion represents the largest kimberlite emplacement event in the pipe and is a typical diatreme facies pelletal tuffisitic kimberlite breccia. The F8 kimberlite represents the highest-grade ore-body and lies within F1 with transitional contacts. F7, which has distinct contacts with F1, represents the third event of economic significance at Finsch and was initially characterised by the presence of abundant peridotite xenoliths. An additional six economically less significant hypabyssal intrusions have also been identified, including internmal crosscutting dykes (F4) and a late stage internal plug (F2) cutting F8.
The presence of Karoo wall-rock xenoliths in the pipe indicates that Karoo rocks existed on top of the Ghaap Plateau at the time of kimberlite emplacement. Subsequent erosion of approximately 600 to 900 m has entirely removed the Karoo sequence and the upper crater facies of the pipe.
For detail 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.
Finsch
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Appleyard C M, Viljoen K S and Dobbe R 2004 - A study of eclogitic diamonds and their inclusions from the Finsch kimberlite pipe, South Africa : in Lithos v77 pp 317-332
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Barnett W, Preece C 2002 - Expanding the geological model for Finsch Mine: in S. Afr. J. Geol. v105 pp 381-400
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Skinner C P, 1989 - The petrology of peridotite xenoliths from the Finsch Kimberlite, South Africa : in S. Afr. J. Geol. v92 pp 197-206
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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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