Basutoland Diamonds

Courtesy of OSPA

by Professor Peter H. Nixon (Geologist, Basutoland and Uganda 1957-73)
Basutoland Diamonds
William Quarrier Kennedy
My life as a diamond exploration geologist began when I started work in 1957 in Basutoland as a member of the Research Institute of African Geology based at Leeds University. The Institute was founded by W.Q. Kennedy, FRS, known to us simply as "W.Q." - a charismatic and brilliant Scottish Geological Survey geologist who obtained 100,000 pounds for starting the Institute in 1953 from Mr (later Sir) Ernest Oppenheimer of De Beers.

W.Q. charmed all who met him. He regaled the Ph.D. students and staff at Leeds with tales of African rift valleys, volcanoes and air travel in flying boats, laced with stories of charging elephants and rhinos.

The Institute's overseas base was in Harare, formerly Salisbury, Southern Rhodesia where W.Q introduced us to another sponsor - the managing director of the Scottish company Keir (& Cawder). We collected a Land Rover which was to transport fellow geologist, Barry Dawson, and me over 1,000 miles south to Basutoland.

Basutoland Diamonds
Leribe Fort
We loaded up with geological, surveying, prospecting and camping gear and launched ourselves southwards towards Beitbridge on the South African border. The roads in Southern Rhodesia at that time lacked tarmac apart from two parallel strips, one for each wheel track - except when passing/overtaking. After several days we arrived in Basutoland, an enclave within South Africa, and headed for the Lowland town of Leribe, altitude about 4,500 feet, which contained the base camp of Colonel Jack Scott who had made a fortune on the Witwatersrand gold deposits of South Africa. He believed that he could also find diamonds in particular in the high mountains of Basutoland (the Maluti) thought to be the source of many diamonds washed down by the Orange River to the diamond alluvial deposits of South Africa and Namibia. This speculation turned out to be prophetic. The paramount Chieftainess of Basutoland sold him a concession to explore anywhere in the Kingdom.

Scott added "the struggling PhD students" to his exploration staff! We then learned the perils of crossing swollen rivers in our Land Rover, and on Basotho ponies. Mules were often our only means of transporting equipment in the Maluti. One particularly wild animal was loaded (with difficulty) with our tents, hammers, spades, buckets, plane tables and our large ancient transmitter for keeping communication with our mountain base at Kao.
Basutoland Diamonds
Maluti Pass
This mule and its train were crowded on a narrow track alongside the headwaters of a large river 500 feet below. It was nudged off the track and fell cartwheeling below; the transmitter burst open and spilt its valves; the mule miraculously staggered back up the 45 degree slope. However, it died shortly after. We were presented with its liver at our tent. We thought that some rump steak would be preferable. That was a great miscalculation - it was like chewing leather!

On the scientific level we learned how to recognize kimberlite, the potential host rock for diamonds, and how to gravitate for "indicator" minerals: chromite, ilmenite, olivine, pyrope, chrome diopside, zircon, etc as well as diamond itself. 'Gravitation' is a swirling and 'jigging' motion applied to a sieve full of kimberlitic gravel in a drum of water. This motion induces heavier minerals, including diamond if present, to aggregate near the centre of the 'cake' of the sieve contents. These minerals are readily seen and extracted when the sieve is overturned on flattened earth or sacking. We explored around Basutoland to Natal to access the highest peaks over 9,000 feet by first driving up the Sani Pass traversing the precipitous Drakensberg escarpment. After passing through Mokhotlong township we sampled dykes of kimberlite near Robert, and lay down in our sleeping bags at night whilst watching the Russian sputnik on its inaugural (1957) journey around the moon.

Sometime thereafter we had to make a decision about who was to take the Land Rover back to Leribe via the Sani Pass, and who was to return to Kao with the team of Basotho workers and equine transport across the roadless and uninhabited Maluti at high altitude and with several awkward river crossings. I 'volunteered' the latter option!

On the 14th of December 1957 my team camped near to a swamp on the Namahali trail. There was a small outcrop of "clay" in a stream that warranted further investigation. After pitting an area larger than the size of a football field it was clear that it was a "pipe" - a truncated (eroded) volcanic neck of kimberlite. My excitement was moderated by the fact that the kimberlite seemed rather poor in the silicate minerals mentioned above, and there were no signs of diamond. My report to Colonel Scott back in the lowlands was brief and occasioned little immediate interest.

Furthermore, the place was a long way from anywhere. The nearest township of Mokhotlong was a walk or pony ride of 27 km.

Basutoland Diamonds
Letseng Diamond Mine
Nevertheless, the site attracted some diggers in spite of the inhospitable winter snow and ice and high altitude - over ten thousand feet (3,200 metres). The kimberlite acquired the name Letseng la terai (swamp on the corner of a bend - on the Namahali track) replacing our name Qaqa, named after a nearby river but which is difficult to pronounce, having two bushman "clicks".

By 1965 there were 1,200 diggers reported, swelling to 6,000 two years later. One of the diggers, Mrs Ramaboa, discovered in the surface gravels the world's 11th largest gem diamond - but slightly brownish, "lager brown", weighing over 601 carats! Interest in the deposit increased.

Rio Tinto were selected by the Basutoland (now Lesotho) government to carry out an orderly geological drilling program and diamond evaluation. The illegal diggers were removed with difficulty.

Perhaps surprisingly, in view of some high value diamonds, including a 47 carat stone in a parcel of 62,000 carats, Rio Tinto abandoned the prospect in 1972 and were replaced by De Beers. Currently, the Gem Diamond company work the Letseng Kimberlite and its satellite pipe. The Kingdom of Lesotho has a stake in the mine and collect royalties.

The pipe has produced 4 large (around 500 carats) diamonds that fall within the world's top 20 gem diamonds. These are beautiful and exceptionally high quality whites. A major problem is that the overall grade (concentration) is only 2.5 carats (half a gram) per 100 tonnes - lower than any other comparable diamond mine, and hence expensive to work. A secondary problem is that the very rare large diamonds can be smashed in the crushers during treatment which results in a multi-million dollar debasement of diamond values. Keith Whitelock who is a recognized authority throughout southern Africa on diamond processing and plant design has doubtless averted such tragedies.

Basutoland Diamonds
Lesotho Promise
He separated and named the most famous of the Lesotho diamonds - the Lesotho Promise - 603 carats discovered in 2006 - from which 26 cut diamonds of top flawless "D" grade have been mounted on a necklace with a 76 carat pendant by Jeweller Mr. Laurence Graff. It is indeed a necklace fit for a Queen.

After the discovery of Letseng the author worked with the Geological Survey of Uganda, before returning to Lesotho to help establish a geological section geared to diamond exploration, within the Mines Department of the Lesotho Government. He is editor of Lesotho Kimberlites.

Colonial Map
1955 Map of Basutoland
Colony Profile
Originally Published
OSPA Journal 111: April 2016


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