Jagersfontein Mine, Jagersfontein, Free State Province, South Africa

A diamond mine in a kimberlite pipe, owned by De Beers. Diamonds were first found at Jagersfontein farm in 1870, but it took until 1878 to recognize that this occurrence was indeed a pipe. It was first worked from an open pit, because the presence of a thick dolerite sheet made the side walls much more stable than those at Kimberley or Koffiefontein. Underground mining only commenced in 1910. The mine was worked almost continuously until 1971, except for two short periods of time during the 1930s depression and the Second World War. Its final closure was due to a decreasing diamond grade and increasing mining costs at greater depths.

Jagersfontein mine produced diamonds of extremely high quality, but the diamond grades were very low. It also produced a number of the world's largest diamonds, among them the 971.75 ct Excelsior and the 640 ct Jubilee (previously named Reitz). Among researchers, the deposit is known as a prime locality for mantle xenoliths, some of which are interpreted to have been derived from 300-500 km depths.

Located 2½ miles from Jagersfontein.

References:
- Dana 7:I:150.
- Mathias, M., Siebert, J.C., and Rickwood, P.C. (1970): Some Aspects of the Mineralogy and Petrology of Ultramafic Xenoliths in Kimberlite. Contributions to Mineralogy and Petrology 26, 75-123.
- Rocks & Min.: 21:130.
- Field, M., Stiefenhofer, J., Robey, J., and Kurszlaukis, S. (2008): Kimberlite-hosted diamond deposits of southern Africa: A review. Ore Geology Reviews 34, 33-75.