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Premier |
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Gauteng, South Africa |
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Diamonds
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Super Porphyry Cu and Au
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The Premier Diamond Pipe is located on the farm Elandsfontein 480JR at the town of
Cullinan, 25 kilometres north-east of Pretoria, in Gauteng, South Africa.
The Premier pipe originally covered a surface area of 32 ha. It is the largest known diamondiferous kimberlite in South Africa and the most important pipe in a cluster of twelve kimberlites in the Cullinan-Rayton area, including the National, Schuller, Montrose and Franspoort pipes. Small alluvial deposits occur downstream of the kimberlites.
The Premier pipe had an elongate oval shape and comprised diatreme facies kimberlite to a depth of 550 metres, below which it grades into the root zone. The pipe intrudes fenitised quartzites of the Transvaal Supergroup and is cut by a 75 metre thick gabbro sill at a depth of 350 metres below surface. The main pipe has been dated at 1180 Ma while the gabbro sill was emplaced at 1115 Ma.
Premier is a complex body with three distinct kimberlite phases corresponding to three main phases of activity, as follows: i). The first phase produced a diatreme of "brown" tuffisitic kimberlite breccia (TKB) in its southeast section, characterised by abundant shale and norite wall-rock inclusions. ii). The second phase forms the main core to the pipe, comprising "grey" TKB, characterised by an abundance of Waterberg quartzite, basement granite and gneiss inclusions, while large blocks of "quartzite floating reef" are present in the middle of the pipe. iii). The third phase is a circular plug like body composed of "black" hypabyssal facies kimberlite, characterised by dark green pseudomorphs after olivine, intrusive into the western part of the pipe. The black hypabyssal kimberlite is intruded by a radial pattern of carbonatite dykes.
The pipe contains a heavy mineral assemblage of ilmenite, garnet and chrome diopside, and xenoliths of harzburgites, lherzolites and eclogites.
The mine commenced operation on 1902, and apart from brief closures between 1914 and 1916, and between 1932 and 1945, it has consistently been a major diamond producer with a high frequency of stones of larger than ten carats. Between 20 and 30% of diamond production is gem quality. The open pit is 190 m deep.
To the end of 1989 some 294 Mt of ore had been mined from underground for 95.88 million carats (19.177 t) of diamonds with an average recovery of 32.6 cpht (carats per hundred tonnes). Open pit mining in the early years is not included. In the year of 1995, it produced over 1.6 million carats or 18% of the South African production at an average grade of 44.6 cpht. The mine has produced about 300 stones of >100 carats, and a quarter of all the plus 400 carat diamonds ever recovered in the world. Of the most famous are the 137 carat Premier Rose, cut from 353 carats, the Niarchos cut from 426 carats, and the 599 carat De Beers Centenary diamond in 1988. However, the most famous of all was the 3106 carat Cullinan Diamond, the largest gem diamond ever found, cut to form the 530 carat Great Star of Africa and 317 carat Lesser Star of Africa set in the Crown Jewels of Britain.
Reserves + resources in 2000 totalled 336 Mt @ 45.8 cpht for 154 million carats of diamonds.
Production in the same year was 2.84 Mt @ 62.6 cpht for 1.782 million carats of diamonds at an average value of USD 46 per carat.
Alluvial diamonds, thought to be derived from kimberlites in the Premier cluster, have been recovered close to some of the pipes, although no alluvial mining is recorded far from any of the pipes.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2002.
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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Bartlett P J 1994 - Geology of the Premier diamond pipe: in Anhaeusser C R 1994 Proceedings XVth CMMI Congress, 4-9 September, 1994 SAIMM, Johannesburg v3 pp 201-213
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Gregoire M, Tinguely C, Bell D R and le Roex A P, 2005 - Spinel lherzolite xenoliths from the Premier kimberlite (Kaapvaal craton, South Africa): Nature and evolution of the shallow upper mantle beneath the Bushveld complex: in Lithos v84 pp 185-205
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Gurney J J, Harris J W, Rickard R S and Moore R O, 1985 - Inclusions in Premier Mine diamonds : in S. Afr. J. Geol. v88 pp 301-310
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Maier W D, Peltonen P, Juvonen R and Pienaar C, 2005 - Platinum-group elements in peridotite xenoliths and kimberlite from the Premier kimberlite pipe, South Africa : in S. Afr. J. Geol. v108 pp 413-428
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Viljoen K S, Dobbe R, Smit B, Thomassot E and Cartigny P 2004 - Petrology and geochemistry of a diamondiferous lherzolite from the Premier diamond mine, South Africa: in Lithos v77 pp 539-552
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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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