First Diamonds In Botswana

FEATURE “In the romantic hunt for diamonds, for the rich pot-holes and jewelpatches in which they sometimes collect, many men have been inclined to lose sight of the strange storehouses from which they have come. That is to say, most men have. On the other hand, some have not.” - Hedley Chilvers, The Seven Lost Trails of Africa, 1930.

First diamonds in Botswana Dr LEON DANIELS

The Orapa discovery pit: Jim Gibson, Dr Gavin Lamont and Manfred Marx

More than two thirds of Botswana is covered by the Kalahari Desert. This almost ubiquitous blanket of sand has long obscured Botswana’s mineral wealth. The country’s first kimberlite pipe was only discovered in 1967 after more than a decade of prospecting. It is only along the eastern sector of Botswana where one finds rocky outcrops and some development of streams and rivers. Three small diamonds were recovered from gravels in the Motloutse River, near Foley Siding, in 1959. These were the first authenticated diamonds to be found in Botswana, discovered by the Central African Selection Trust (CAST). The prospecting team followed the seasonal river to its headwaters, but eventually abandoned their search under the belief that the diamonds were derived from local Karoo age conglomerates. The project was terminated. De Beers had begun prospecting in Botswana in 1955. One of their first recruits was Dr Gavin Lamont who had been working at the Geological Survey of Bechuanaland Protectorate (Botswana today). After traversing large areas of the country and sampling the blanket of sand for minute indicator minerals, Lamont finally decided to focus on the eastern central part of Botswana. In 1963 he was joined in his search for kimberlites by Jim Gibson, a young Scot. After eight years of prospecting De Beers had still not found a single kimberlite. Rough Diamond Review

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In 1964 Lamont decided to return to the site of the original discoveries by CAST. By now their data was an open file which he could study and evaluate. Lamont discussed the results with Chris Jennings, a young South African geologist working at the Geological Survey on the geohydrology of the country. Jennings directed Lamont to a paper written by Dr Alex du Toit, the South African geologist credited with the theory of continental drift and Gondwanaland. Of interest was Du Toit’s identification of a warp in the crust of the Earth that stretched from Bulawayo in Zimbabwe to the southern parts of Botswana. Lamont noticed that the headwaters of the Motloutse River terminated against the crustal upwarp identified by Du Toit. It was possible that the Motloutse River could have been spliced in two by the upwarp and that both the Motloutse River and the diamonds it contained could have an origin further to the west, on the other side of the upwarp. Lamont sent a report to the De Beers head office, but received no reply. Two years later Botswana was approaching its independence. Still unsuccessful, De Beers were ready to terminate their exploration in Botswana.

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BOTSWANA However, Lamont wanted to test his interpretation of Du Toit’s warp theory once and for all. There had been a change at head office and the new man in charge of exploration, Louis Murray, granted a three month extension to the exploration programme - more out of respect for Lamont’s tenacity than out of optimism.

The latter two pipes were brought into production as the Lethlhakane Mine in 1977. The DK1 pipe is characterised by an elevated topography in the form of a calcrete hill adjacent to the Lethlakane River. Ironically, Alex du Toit had already recorded this hill during a mapping exercise in the 1930s. The last kimberlite to be discovered in the Orapa field during this initial phase of exploration, 2125B/K16, was also the first kimberlite to be discovered in Botswana with the use of airborne magnetic surveys. The discovery of the Orapa field changed the De Beers’ view of Botswana’s exploration potential and their activity increased significantly. Lamont was given a budget to hunt for kimberlites in elephant territory. Just as the first phase of exploration decreased in the Orapa area, activities increased elsewhere leading to the discovery of the Jwaneng kimberlite field, approximately 150 km west of the capital, Gaborone. The main exploration method was systematic soil sampling of surface Kalahari sediments.

Indicators: In only three months Lamont and Gibson had to cover an area of approximately 4600 square kilometres. Traditional methods of sampling along traverse lines could not be followed as it would be too slow. The two geologists set off in two vehicles following every track made by hunters and cattle farmers throughout the vast area, and collecting soil samples at regular intervals. They returned the samples to the camp for washing and screening. By the time they found what had been eluding them for so long, the tiny ilmenites and garnets that lead the way to kimberlites, the search had to be postponed while other projects were finished off. They still had no proof that they had found diamonds, but they knew they were on the tracks of a kimberlite. During this waiting period their team was expanded by a recent graduate geologist from Cape Town, Manfred Marx. When they resumed exploration in the area results followed rapidly. Firstly a five hectare kimberlite designated 2125B/ K1 was discovered, rapidly followed by 2125B/K2. Both these kimberlites were characterised by positive topography. In April 1967 Marx contacted Lamont by radio to report that fantastic indicator counts were being obtained in a particular area. They studied aerial photographs of the area and found a very large vegetation anomaly. This turned out to be a feature regularly used by pilots as a navigation point when 1 KILOMETER they flew over that part of Botswana. The surface area was too large for Lamont to consider it a single pipe and he thought it might be an alluvial An aerial photograph (1960) showing the vegetation anomaly associated feature of some sort. Nevertheless, with the Orapa pipe. Other smaller kimberlite pipes can also be seen in the he instructed Marx to dig a pit and set area to the east and south-east of Orapa. off with Jim Gibson to join Marx in the field. In the afternoon of 19 April Magnetics: The first kimberlite 2424D/K1 was 1967 Manfred Marx climbed out of the pit late with the drilled in 1972. This was followed by the discovery first piece of kimberlite from the world famous 113 ha of 2424D/K2 in 1973. The latter kimberlite was 2125A/K1 kimberlite – Orapa. approximately 40 – 45 metres beneath Kalahari The Orapa kimberlite was named after a formation sediments and consisted of the coalescence nearby cattle post and the mine was officially opened of three diatremes in a single crater with a surface area in 1971 at a development cost of ZAR 21 million. It has of 54 ha. The kimberlite had a very poor magnetic an age of 93 Ma and is situated within the Zimbabwe expression, but was characterised by a distinct gravity Craton. The majority of the diamonds are eclogitic in ‘low’. This 235 Ma old kimberlite became known as origin. the Jwaneng Mine which was described by Harry By the end of 1972 a total of 30 kimberlite Oppenheimer at the official opening of the mine in discoveries had been made in the Orapa field, 1982 as ‘the most important discovery of the century‘. including the Letlhakane 2125D/K1 and K2 pipes.

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Rough Diamond Review

SEPTEMBER 2004

BOTSWANA ANGOLA

Ok

ZAMBIA

n av a

CHOBE

go

Tsodilo

NGAMILAND

Boteti

ZIMBABWE H RT NO

NAMIBIA

Orapa

FRANCISTOWN

ST EA

Letihakane

FOLEY SIDING

GHANZI O

CENTRAL

a kw

Gope Martin's Drift

Okwa

Khutse Kukong

KGALAGADI Mabua Sehube

KWENENG Jwaneng

KGATLENG

GABARONE

SOUTHERN

Tshabong

SOUTH AFRICA

100 KILOMETERS

which is similar in size to the Jwaneng kimberlite. An interesting feature noticed in this kimberlite field was that while the majority of the kimberlites were represented by magnetic ‘high’ signatures, some (e.g. T45) were characterised by magnetic ‘lows’. In the Kukong area Falconbridge discovered 21 kimberlites. The most interesting was the KN 70 kimberlite with a possible grade of 10 cpht. Although most of the kimberlites had some crater facies associated with them, only hypabyssal facies kimberlite was interesected at the KE1 kimberlite. This kimberlite was also the only kimberlite associated with a gravity ‘high’. In this area, Falconbridge also discovered a number of carbonititic intrusives, the largest being KW2 with a diameter of 4 kilometres. Meanwhile, De Beers was investigating the area between Tshabong and Kukong. They discovered a cluster of non-diamondiferous kimberlites or lamproites at Mabua Sehube. Reinforcements: Following their successful discoveries of kimberlite in both the Tshabong and Kukong areas, Falconbridge and their joint venture partner Superior Oil decided on a large regional soil sampling programme over the central part of Botswana. However, before embarking on this exercise they wanted a system to rate kimberlite indicators for diamond potential. John Gurney, from the University of Cape Town in South Africa, had published a paper in 1973 relating diamond inclusion garnets to concentrate garnets in the host kimberlite. Chris Jennings turned to John Gurney to develop a system of indicator assessment for Falconbridge.

A total of 11 kimberlites were discovered in this field although 2125D/K7, a 5 ha bilobate diatreme, was the only other discovery of economic interest. While working at the Geological Survey, Chris Jennings developed a model to search for kimberlites using aeromagnetics. Eventually Falconbridge, the Canadian nickel company, decided to support his ideas. They began investigating areas to the east of Orapa, but without success. In 1976 an international journal published a paper detailing those areas in Botswana characterised by kimberlite indicators in the soils, as reported by De Beers exploration activities. Falconbridge immediately applied for prospecting licences in two of the areas where no kimberlites had been discovered. These were granted in 1977 and Falconbridge used the airborne technology. Their results were exciting. Both in the Tshabong area, in the south western part of the country, and in the Kukong area further to the north, they identified several aeromagnetic targets to investigate. In the Tshabong area the main target was identified as M1 being the first anomaly identified in the Molop project area. Ground crews were sent to locate the target on the ground, which was enormous, An evaluation camp is established next to the 110 hectare Orapa in excess of two square kilometres. An pipe, which can be seen in outline behind the camp. (1968) old jumper drill was despatched and kimberlitic sediments were discovered at a depth of 80 metres. After two years of John Lee, from Falconbridge, provided the delineation drilling the largest recognised kimberlite in mineral chemistry data on the kimberlite indicators the world, the 77 Ma old, 200 hectare M1 kimberlite collected during their exploration programmes and was earmarked for bulk sampling. In addition to the orientation surveys. In addition, Gurney sent a young M1 pipe, Falconbridge under the guidance of Chris geology student from the University of Cape Town, Jennings discovered another 39 kimberlites in the Leon Daniels, to sample kimberlites in the Kimberley area including the trilobate T6 kimberlite of 54 ha, and Karoo area of South Africa. The Karoo kimberlites Rough Diamond Review

SEPTEMBER 2004

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BOTSWANA were in the main off-craton kimberlites. With all the information, being prior to the advent of personal computers, Gurney needed help to compile and assess the data. He was assisted by John Bristow from the university and Andy Moore, who had recently joined Falconbridge and was conducting the central Botswana sampling programme. The initial result of the sampling programme identified an area in the Central Kalahari Game Reserve as being a target zone where two 0.5 mm ilmenites were recovered. Falconbridge flew an aeromagnetic survey over four prospecting licences and Chris Jennings identified a target designated Go 25. (‘Go’ stands for ‘Gope’ which means ‘nowhere’). A geologist

Some early diamonds from Orapa.

was sent out to locate the target on the ground, soon followed by a jumper drill. The drilling interesected a kimberlite below approximately 80 metres of cover. The indicators were sent to Gurney for analysis as he was completing his mineral chemistry assessment method. The heavy mineral suite of the newly discovered kimberlite contained a large number of garnets that Gurney recognised as being significant in identifying potentially economic kimberlites. Falconbridge had found their first potential diamond mine in Botswana. It was late 1981, there was great excitement and bulk sampling followed. De Beers had taken note of Falconbridge’s increased activities. The company was approached and a joint venture was agreed upon. De Beers took over the management of the Falconbridge diamond programme. The Falconbridge kimberlite exploration team, the most successful at that time in the world, was disbanded and Falconbridge soon ceased all diamond exploration. More than twenty years after discovery it seems as though Falconbridge’s kimberlites may never be mined. Revival: During most of the 1980s there was little kimberlite exploration in Botswana and only a few discoveries were made. The Central African Selection Trust (CAST) returned to the country. They became BP Minerals and eventually evolved into Rio Tinto Exploration. Rio Tinto has since maintained a steady programme of exploration in Botswana. Gencor and TransHex have attempted exploration, but met with limited success in new discoveries.

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Interest in diamond exploration heightened once again in the late 1980s and early 1990s. De Beers started to reinvestigate the Orapa field and subsequently discovered more than 40 additional kimberlites in the general area. In addition, they have re-sampled some of the first phase kimberlites and have commenced operations at the Damtshaa Mine in the Orapa area, mining kimberlites BK9, BK12 and in future BK15 and parts of BK1. They have also studied the alluvial potential associated with the main AK1 pipe and may also mine alluvials. De Beers have explored other areas in Botswana, finding a cluster of kimberlites in the west (Okwa valley) with Mark Scowcroft supervising the programme in the field. In the southeast another programme discovered the Martin’s Drift kimberlites. Two ages of kimberlites were discovered in this field, including the main, nonmagnetic cluster of 1333 Ma. De Beers eventually attempted to mine the older kimberlites. After a five year period of ‘trial mining’, they closed down the operation. Andy Moore, together with Paul Larkin, formed Ampal. This was the first diamond exploration company in Botswana to raise private shareholders funds, used for exploration around Orapa and to the west of Jwaneng. The main exploration technique was aeromagnetic surveying followed by soil sampling. Ampal identified areas of interest, but were unsuccessful in discovery. They formed a joint venture with De Beers and eventually, a diamondiferous kimberlite was discovered in the western area. Numerous Canadian junior companies and a number of Australian juniors have undertaken diamond exploration in Botswana. Auridiam Consolidated (from Australia) obtained a prospecting licence to evaluate five kimberlites that discovered in the first phase of exploration by De Beers. They formed a joint venture with a Canadian Junior, but the exploration programme was unsuccessful. Redaurum Limited (from Canada) discovered another kimberlite to the east of Lethlakane, but recovered no diamonds. With the advent of the Bre-Ex scandal, junior companies generally disappeared from Botswana’s exploration scene and as the twentieth century ended, it was mainly the major companies exploring for diamonds. However, Botswana was now firmly on the world map of diamond production and had three of the world’s greatest mines, discovered by Gavin Lamont and his team, firmly in production and expanding. The introduction of new technology to ‘see through the Kalahari blanket’ and improvement of tried and tested techniques heralded a new hunting season for kimberlites in elephant country.

Dr Leon Daniels lives in Botswana and has had 22 years experience in diamond exploration and mining in Africa, including Swaziland and Angola. He is currently working as a consultant to diamond and gold mining companies. Email: [email protected]

Rough Diamond Review

SEPTEMBER 2004