The Orapa mine in Botswana is in the midst of a US$400-million expansion project aimed at boosting annual production to 12 million carats. Consequently, the mine life will be halved to 30 from 60 years.
The mine’s owner, Debswana Diamond Co., dominates diamond mining in the southern African nation. Orapa, together with Debswana’s two other mines, Jwaneng and Letlhakane, enabled the company to report production of 20.1 million carats in 1997, compared with 17.7 million carats in 1996. In 2000, once the Orapa expansion is complete, Debswana’s total annual production will rise beyond 25 million carats.
Situated about 250 km west of Francistown in the northern part of the country, Orapa entered production in 1971 at a design rate of 2.5 million carats per year. The plant’s capacity was doubled in 1979. In terms of area, Orapa is one of the world’s largest kimberlite pipes being mined: it covers 117 ha. In 1997, Orapa produced 6.7 million carats from the treatment of 8.6 million tonnes of ore, equal to a grade of 78.9 carats per 100 tonnes. The diamond value is believed to average US$60 per carat.
Debswana has applied for a mining lease on the B/K9 kimberlite, a much smaller 10-ha pipe some 10 km east of the mine. Grades are believed to be in the range of 15 carats per 100 tonnes, with stones valued at US$80 per carat.
Continued exploration in the early 1970s uncovered two payable but smaller pipes at Letlhakane, 40 km southeast of Orapa. Letlhakane started operations in 1977 at a rate of 300,000 carats per year, rising to some 400,00 carats in 1980 and to more than 1 million carats by 1994. In 1997, the mine recovered 893,456 carats from the 3.5 million tonnes of treated kimberlite, equivalent to 25.8 carats per 100 tonnes. Production is reported to average US$150 per carat.
The 51-ha Jwaneng pipe was discovered by De Beers geologists in 1973, about 120 km west of the capital city of Gaberone. It was advanced to feasibility in 1978 and put into production in 1982. The open-pit mine produced 12.5 million carats from 9.1 million tonnes of processed ore in 1997, for a grade of 137.5 carats per 100 tonnes. Jwaneng’s stones average a value of US$100 per carat, making it one of the world’s richest pipes. Its life is pegged at 30 years.
De Beers was awarded a 4-year mining lease in 1997 to exploit five small diamondiferous kimberlite pipes at Martins Drift in eastern Botswana on the border with South Africa, 400 km east Gaberone. Site preparation and construction of a diamond treatment plant were completed in mid-September 1997, and by year-end some 25,000 tons of the resource had been sampled.
In 1997, further detailed prospecting by De Beers in the Orapa and Mochudi areas resulted in the discovery of new but uneconomic kimberlites.
A prefeasibility study was completed on the Gope-25 project in central Botswana, held in equal partnership with
De Beers Prospecting Botswana formed a new joint venture with Toronto-based
Initial microdiamond analysis yielded: 10 macros and 20 micros from a composite 478.26-kg drill sample of the Bay pipe; 5 micros from 501.6 kg of the Wall kimberlite; 2 macros and 10 micros from a 267.2-kg sample of the Diagonal pipe; and zero stones from a 124-kg sample of the King pipe. (TNK defines a macro as measuring more than 0.5 mm in at least one dimension.)
The Gope area is overlain by sands of the large Kalahari basin, varying from 40 to 60 metres in depth on TNK’s ground. Previously, the sands posed a major challenge in identifying the underlying kimberlites. To complicate matters, the barren country rock in the region has a magnetic susceptibility similar to that of kimberlite.
However, with the aid of today’s improved geophysical survey processing technology, TNK was able to reprocess two previously flown aeromagnetic surveys by Falconbridge and Rio Tinto to reveal 159 potential targets for follow-up.
Early regional work by Falconbridge in the Gope area recovered a few scattered kimberlite indicator minerals and was followed by an airborne magnetic survey. In total, 41 targets were selected for follow-up sampling and ground magnetic surveys. Five kimberlite pipes, known collectively as the Kikao Swarm, were discovered in the southwestern part of the permits. Microdiamonds were reported in each of the pipes.
De Beers entered into a joint venture with Falconbridge and blanketed the property with reconnaissance heavy mineral sampling, collecting some 25,000 samples. De Beers’ work resulted in the discovery of two more kimberlite pipes and four dykes, while delineating a generally northwesterly trending indicator mineral anomaly across what is now TNK’s 1-million acre Gope property.
Tinto Botswana, a subsidiary of Rio Tinto, licensed the northern portion of the Falconbridge-De Beers area in 1988 and conducted geophysical surveys and sampling programs before relinquishing the licences in 1993. Rio’s work resulted in the discovery of at least one new kimberlite pipe, northeast of the Kikao Swarm.
By meeting certain expenditure and work commitments, De Beers can earn varying interests in the 1-million-acre TNK Gope property, which is divided into three areas, the first being the licence covering TNK’s four kimberlite discoveries.
De Beers is the operator of the 174-sq.-km Area 1 joint venture and can earn up to a 60% interest by funding all exploration and development costs, including a full feasibility study. The Botswanan prospecting arm of De Beers first re-tested 14,740 kg of drill material from the four pipes for macrodiamonds greater than 1 mm. The richest sample came from the Bay pipe, which yielded 1 macro weighing 0.24 carat.
A sample from the Wall pipe returned 4 macros with an aggregate weight of 0.21 carat. A single stone weighing 0.025 carat was recovered from a sample of the Diagonal pipe, and a sample of the King pipe contained no macros.
De Beers carried out a follow-up program of mini-bulk drill sampling on the four pipes, completing twenty-one 8.5-inch holes for a total of 3,212 metres. The samples are currently being treated at De Beers’ lab in Kimberly, South Africa.
In addition, 645 soil samples were collected from Area 1 to aid in further defining drill targets.
TNK remains the operator of Area 2, which covers the western portion of the property, and Area 3, which covers the eastern region, and which, in turn, surrounds the Gope 25/136 pipe cluster. Area 3 also contains the Howe kimberlite, discovered by TNK in 1996. If TNK makes new discoveries, De Beers will have the option of becoming the operator and will have the right to earn up to a 60% interest by advancing the licences through to the feasibility stage.
TNK contracted De Beers to conduct soil sampling of 54 target areas in both Areas 2 and 3 over the course of the summer. Indicator minerals were recovered from 28 of the target areas. In November 1998, a limited program of reverse-circulation (RC) drilling further tested t
he Howe kimberlite in Area 3, as well as a nearby geophysical anomaly, which, on the basis of initial examination of the rock, has been judged not to be kimberlite. Samples from the Howe kimberlite are being analyzed for microdiamonds.
In January of this year, Monopros, the Canadian exploration arm of De Beers, completed the second half of an $800,000 private placement of TNK. The second tranche, worth $400,000, consists of 400,000 units of TNK at $1 per unit. Each unit includes one share and one warrant entitling the purchase of an additional share at $1.50 by March 12, 2000.
De Beers has continued exploring in areas held under joint venture with
AfriOre is negotiating to farm out its Kokong and Gope licences to a third party.
Farther to the southeast,
Contiki is required to spend US$4.8 million on exploration over five years and issue 1 million shares to Layfield.
The Molopo properties consist of eight prospecting licenses covering approximately 3,582 sq. km, of which licence 139/93 comprises 836 sq. km. Southern Africa acquired the licences in 1993.
In the period 1978-1980, Falconbridge discovered 38 kimberlite intrusions in the greater Tsabong area, 31 of which are on the present Molopo property. An additional 20 kimberlites were found by Southern Africa, bringing to 58 the total number of known intrusions.
On licence area 139/93, Falconbridge has identified 28 kimberlite pipes. Eleven of these are diamondiferous, including the M-1 pipe, thought to be the world’s largest kimberlite, with a surface area of 180 ha. Of the 28 pipes, half were discovered by Falconbridge; the other half were new discoveries by Southern Africa. The microdiamond counts range up to eight stones per 50-kg samples.
The M1 kimberlite is the only target on which detailed work and evaluation drilling were carried out. Falconbridge collected a 365-tonne mini-bulk sample from the pipe using large-diameter drilling. Only three macros were recovered from the crater facies rocks of M1, using an on-site pan plant. Falconbridge drilled several deep core holes into the pipe, including one hole, M1-56, in a joint venture with De Beers. The hole was stopped in tuffisitic kimberlite breccia at a depth of 404.1 metres. The final 10.1 metres had an extrapolated grade of 3.68 carats per 100 tonnes.
In 1998, several of the old core holes were re-sampled by Layfield. In total, 20 samples, weighing 25-30 kg each, were collected from holes M1-53, 54 and 56. Fifteen stones were recovered, with the two largest stones measuring 1.23 and 0.86 mm in their longest dimensions.
Contiki is in the midst of a minimum 12-hole program of RC drilling. The first two holes of this program have intersected kimberlite 80 metres beneath the Kalahari sands while testing geophysical targets 94-39 and 94-41A. Anomaly 94-39 is interpreted to have a minimum size of 7 ha, whereas 94-41A is estimated to be 2 ha. Samples are being sent to Lakefield Research in Ontario for microdiamond and chemical analysis.
Contiki intends to test seven previously undrilled geophysical targets and re-test five known kimberlite pipes.
At Molopo, Layfield discovered six kimberlites during an 8-hole program of RC drilling in the fall. The geophysical signatures of the new discoveries average 7 ha in size, with the three largest bodies each exceeding 12 ha.
Recent microdiamond analysis from the first two Layfield discoveries yielded 2 micros from a 50-kg sample of 98-1, which is now referred to as the Antelope kimberlite. No stones were recovered from a 50-kg sample of anomaly 98-87.
Layfield can earn a 75% interest in the Molopo licences from Southern Africa by spending US$5 million on exploration over four years and delivering 1 million shares of Layfield, plus 500,000 shares of Southern Africa, which it holds. Layfield can count Contiki’s required expenditures toward those obligations.
In the meantime, Southern Africa drill-tested a 6-to-7-metre-thick kimberlite dyke with three widely spaced holes along a strike length of 700 metres at its wholly owned Mosomane property, 50 km north of Gaborone. The dyke was intersected at a depth of 30 metres. One of the six 30-kg drill samples returned one macro (+0.5 mm) and six micros. The other five samples were barren of diamonds.
Elsewhere on the property, a near-surface kimberlite sill, which yielded 3 micros from a 43.5-kg trench sample, was further tested with two holes. No diamonds were reported.
In January 1998, Ashton Mining of Australia entered into a joint venture on the Ngami project in northwestern Botswana. The company can earn a half-interest in the project, which covers some 26,000 sq. km of tenements, west of the Okavango Delta and south of the Tsodilo Hills. Helicopter-borne magnetic surveys confirmed the original aeromagnetic work, which identified several clusters of anomalies as potential kimberlite pipes. Follow-up indicator mineral sampling supported a kimberlite source.
Drill-testing of selected targets began in late January 1998, and, as a result, 14 kimberlitic bodies were discovered. Microdiamond analysis of the first 10 kimberlites yielded a single microdiamond in two of the bodies. At least seven additional aeromagnetic targets were slated to be drill-tested when work resumed in September.
Elsewhere in the central region, Botswana Diamondfields decided not to proceed with any further sampling on the Deception Pan and Mopipi licence blocks after it was unable to define a probable kimberlite source from the indicator mineral concentrations. The company has now closed its field office in Botswana.
MIT can earn a 60% interest in the Orapa property from Auridiam Botswana, a subsidiary of Australian-listed Auridiam Consolidated, by completing a prefeasibility study, due March 1.
The company has negotiated a non-brokered private placement of 1.3 million shares priced at US21 cents each. Proceeds will be used to fund the company’s work programs in Botswana.
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