AIM-listed Botswana Diamonds believes that modern technologies have helped unlock the potential for new kimberlite discoveries in the Free State, and in so doing have helped it focus on specific projects where it will now advance to a phased drilling programme.
The potential of the Free State to host further commercial kimberlites was first identified following research in various archives into the history of diamond mining in South Africa.
This research found that in addition to the well documented iconic operations at Jagersfontein, Koffiefontein and Kimberley, a number of smaller diamond mines existed both to the east of Bloemfontein and extending west to Kimberley.
Research undertaken by Botswana Diamonds notes that the diamond industry as a whole was active up until the early 1880s, but that "a wave of financial collapse and depression swept over South Africa...." such that ..."even old established diggings like Jagersfontein, Dutoitspan and Bultfontein were partially abandoned and younger [smaller] mines.... were totally deserted".
It is evident that attempts were made to re-open these “smaller” mines in the early 1900s but these were frustrated through bureaucratic intervention due to conflicting laws in the lead up to the accession by the Free State Colony into the Union of South Africa.
The result was that permission to restart the mines was not granted, these mines have never been reopened, and their history lost with land ownership changes over time.
Aerial imagery and ground truthing have partially completed the jigsaw which has enabled the company to focus its attention on areas within its Koppiesfontein, Poortjie, Swartrandsdam and Tafelbergsdam properties where historic workings and abandoned equipment are clearly evident.
Available archived diamond certificates in respect of limited exploration activities around Tafelsbergsdam issued in 1898 disclosed recovery of 111 carats of diamonds valued at approximate £93 each which is estimated by Botswana Diamonds to be in excess of US$300/ct in today’s money.
Following the initial document research work and ground truthing, the company has turned to modern science. This started with the taking of ground samples for whole rock geochemistry tests by the Council for Geosciences.
The results of these tests and observations confirm the existence of eight kimberlites which exhibit Group 1 kimberlite geochemistry similar to the larger producing mines of Kimberley and Koffiefontein in the region. The existence of extensive historical working supports the nature of these kimberlites as being diamondiferous.
Detailed ground geophysics followed which produced minimum sizes for the two clusters of eight kimberlite pipes of between 0.3 and 1.15 ha. This excludes extensive kimberlite dyke development along some of the properties.
These sizes were determined using a combination of magnetic, electromagnetic and gravity geophysical techniques, which has resulted in strong images of the footprints of these kimberlites.
Mineral chemistry work was then undertaken to rank the kimberlites from the perspective of diamond bearing potential. The analyses of 3 100 garnets and spinels at the University of Johannesburg indicate high abundances of diamond inclusion type chemical compositions, thereby rating these kimberlites as being of high interest in terms of diamond bearing potential.
The results also indicate a preponderance of G9 and a few G10 garnets, similar to the chemical signatures present in the neighbouring iconic mines at Jagersfontein and Koffiefontein.
The mineral chemistry result supports the conclusions from the previous whole rock geochemistry and from the geophysics in addition to field observations. Botswana Diamonds’ directors believe it justifies moving to a phased drilling programme.
John Teeling, Chairman, comments,
“The Free State story is a fascinating one. Starting from document archives from well over a hundred years ago where some of these kimberlites were diamond producers to modern exploration using whole rock geochemistry, kimberlite mineral chemistry through to detailed ground geophysics. The next step is clearly drilling to determine the kimberlites current commerciality.”