Botswana recovers 11 diamonds and 'abundant' kimerlitic indicators

Botswana Diamonds announce the recovery of 11 diamonds and “abundant” kimberlitic indicators from drill samples at the recently-discovered River kimberlite pipe on Monday, at Thorny River in South Africa’s Limpopo Province.

The AIM-traded firm said that following a “detailed” ground geophysical programme in October, six six-inch percussion reverse circulation holes were drilled into the newly-discovered pipe, with a combined total of 39.5 metres intersecting kimberlite, and an additional 55 metres intersecting a weathered kimberlite breccia.

It said samples from the holes were taken at one metre intervals, and 20 of those, totalling about 500 kilograms, were selected and submitted to an independent processing facility for assessment through screening, dense media separation and hand sorting.

A total of 11 diamonds, 172 G10 pyrope garnets, 623 G9 pyrope garnets, 555 eclogitic garnets, 438 chromites and 268 chromium diopsides were recovered.

Recoveries of a specific mineral species were capped at 20 grains, and thus the board said the results were a “snapshot” of the overall sample indicator content.

It noted that all of the samples contained “abundant” kimberlitic indicators.

The diamonds were all of good colour and clarity, and were of commercial quality of a type in high demand.

Botswana said the diamonds were not weighed, as the sample size was small, adding that they were not representative of a possible population.

Pyrope garnets were common in peridotite xenoliths from kimberlite pipes, the company explained, some of which are diamond-bearing.

It said pyrope found in association with diamond commonly had a chromium oxide content of 3% to 8%, which imparts a distinctive violet to deep purple colouration, which are called G10 and G9 pyrope garnets.

Eclogites typically result from high-to-ultrahigh pressure metamorphism of mafic rocks at low thermal gradients, as they were subducted to the upper mantle in a subduction zone, with garnets found in eclogitic xenoliths tending to have a deep orange colour.

Diamonds in kimberlite come from both peridotitic and eclogitic xenoliths, so the abundance of both types of garnet in the sample was said to be “noteworthy” by the firm, supported by the recovery of diamonds from a relatively small drill sample.

The next step would be a detailed core drilling programme, which was planned for the dry season.

“The recovery of so many kimberlitic indicators and in particular diamonds, which are very rare to recover in small sample narrow reverse circulation drill holes is highly encouraging and bodes well for the potential commerciality of this exciting discovery,” said chairman John Teeling.

At 0856 GMT, shares in Botswana Diamonds were up 8.24% at 0.92p.