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Jagersfontein |
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Free State, 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 Jagersfontein kimberlite pipe is located some 130 km SSE of Kimberley and 109 km SW of Bloemfontein in the Free State of South Africa (#Location: 29° 45' 50"S, 25° 25' 10"E).
Jagersfontein and the similar Koffiefontein pipe, 50 km to the NW, lies within a NW-SE trending structural corridor that embraces a small cluster of kimberlite pipes and dykes which intruded Mesoarchaean basement gneisses and schists, the Neoarchaean Ventersdorp Supergroup and the Jurassic Karoo sequence.
The Jagersfontein pipe was the first diamondiferous kimberlite found in South Africa and is the only economically important intrusion in a cluster of pipes and dykes. It was mined during two separate periods from 1870 to 1931 and from 1949 to 1971, and is currently dormant.
The original surface area of the pipe was about 12 ha. It has been dated at 86 Ma and comprises diatreme facies kimberlite intruding both Permian Karoo shales and dolerites of the upper Ecca Group, which unconformably overlies the Archaean Kaapvaal craton.
The diamond population from the Jagersfontein kimberlite is characterised by a high abundance of eclogitic, peridotitic and a small group of websteritic diamonds. The majority of inclusions indicate that the diamonds are formed in the subcratonic lithospheric mantle. Inclusions of the eclogitic paragenesis, which generally have a wide compositional range, include two groups of eclogitic garnets (high and low Ca) which are also distinct in their rare earth element composition. Within the eclogitic and websteritic suite, diamonds with inclusions of majoritic garnets were found, which provide evidence for their formation within the asthenosphere and transition zone between 250 and 450 km depth (Tappert et al., 2005). The pipe is also rich in mantle xenoliths, some of which are believed to have come from depths of 300 to 500 kilometres.
The total production has been estimated at 11 millions carats, and includes some of the largest gem ever found, the 997.5 carat Excelsior, the 657 carat Jubilee, and two un-named stones of 597.4 and 565.8 carats respectively. These contributed to the pipes reputation for stones of exceptional size and quality. The term 'Jagers' has been used to denote the distinctive faint bluish tint of the gems from this mine (after De Beers Kimberlite Handbook).
The most recent source geological information used to prepare this decription was dated: 1995.
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.
Jagersfontein
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