Mining > Koidu Kimberlite Project > From Pit to Polish
From Pit to Polish
Click on one of the processes in the diagram below to learn more about what's involved.
Blast Layout
In order to minimize damage to the vertical pit sidewalls and to monitor grade variations, the vertical pit has been divided into six Grade Control Areas, the boundaries of which are related to the geology of the kimberlite pipe. In a typical month, each of these Grade Control Areas will be blasted once.
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Drilling of blastholes in the
vertical pit.
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Fragmented kimberlite
after
the blast.
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A system has been developed to follow the movement of ore from the pit, to the stockpile, through the plant and final recovery, to the valuation and export of the diamonds. This means that each diamond sold can be traced back to the location from which it was mined. Each blast is assigned a Blast ID, which references the ore source, the grade control area and the upper and lower elevations of the blast. The area to be blasted is surveyed and the blastholes planned and laid out for drilling.
Support & Production
After drilling, charging and blasting, the fragmented kimberlite is loaded by excavator and moved to the loading pad ready for hoisting to surface by kibble. The kibbles are tipped into articulated dump trucks which transport the ore to the stockpile at the plant. Each kibble load and truck load is counted and labeled according to the blast area and then offloaded in the stockpile dedicated to ore from that specific blast. The movement of ore is tracked by a tailor-made Access database.
Scheduling of activities within the vertical pit is important because at any one time, drilling for the next blast as well as loading and support of the sidewalls from the previous blast will be taking place concurrently.
Processing
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| Sorting of concentrate in sealed glove boxes. Tracer testing monitors the effectiveness of the recovery process. |
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| Surveying of stockpiles and waste dumps |
The ore is processed on a blast by blast basis, with diamonds recovered from each blast area being sorted, classified and consolidated into a diamond parcel ready for valuation.
The current 50 tonne per hour processing plant at Koidu was supplied by sister company BATEMAN Engineering. Since the 1970s, BATEMAN has designed, engineered, procured and construction managed the processing and materials handling facilities on most of the world's largest diamond mines and is the world leader in the supply of permanent and modular diamond process plants.
The Koidu kimberlites are relatively competent (hard and difficult to crush) compared to most other kimberlites around the world. In order to release the diamonds trapped inside the kimberlite, it is necessary to blast the rock into fragments that are small enough to be handled by earthmoving equipment and transported to the plant stockpile area prior to being fed into the processing plant. The main mechanisms involved in the liberation of diamonds from kimberlite are crushing, scrubbing (washing) and gravity separation.
Once inside the plant with its three crushing circuits the kimberlite is reduced to smaller size fractions, which are channeled to the Dense Media Separation Plant. The crushed kimberlite and ferro-silicon mixture is pumped through a cyclone where separation takes place. Gravel with a specific gravity of 2.9-3.05 and above (the 'concentrate') reports to the underflow of the cyclone and gravel with a specific gravity of less that 2.9-3.05 (the 'floats') reports to the overflow of the cyclone. The concentrate, which contains the diamonds, is washed to recover the ferro-silicon and is then pumped to the Recovery Plant.
The Recovery Plant is a containerized gravity fed plant. The concentrate is pumped to the top of the plant where it is de-watered and sized into fractions which are fed separately to the fine and coarse X-Ray machines. The product extracted by the X-Ray machines reports to secure glove boxes for final sorting. The X-Ray tailings report to a grease screen where non-fluorescent diamonds are recovered.
The Thickener Plant is part of the water management system introduced to conserve and re-use water.
A water dam has been constructed to retain rain water for use in the plant. In the plant, all slimes generated reports to the de-grit section where the solids are separated from the water by means of a hydro-cyclone. The under flow of the cyclone reports to a de-watering screen and the overflow of the cyclone reports to the high rate thickener where the slime is treated with an inert flocculent which causes the solids to settle. The slime is pumped to a slimes dam in which the solids are discharged for settling and the clear water generated is returned to the raw water dam.
Valuation and Export
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| Diamond parcel prepared for valuation |
Classification and valuation of diamonds |
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| Diamond valuation at the Government Diamond and Gold Office in Freetown |
Classification and valuation of diamonds |
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Diamonds from Sierra Leone are unique, being easily identified by their octahedral crystal habit and the shape of the coated stones. The characteristics of the diamonds in terms of colour, stone sizes (carats), clarity and shape (cut), have placed them in high demand in the international diamond market.
The Koidu kimberlites are known for their high proportion of special stones. The stone size distribution tends towards a large stone producer, influencing the average price per carat considerably. In addition, the trend in the diamond market towards the fashionable 'fancy' cuts and the high percentage yield from the distinctive octahedral crystals recovered at Koidu, adds considerable value to the overall selling price of the stones. The clarity of the diamonds is good, but the high proportion of non-colour stones sets the Koidu diamonds apart from other producers. The average price of Koidu diamonds is among the highest of the kimberlite producers.
The diamonds produced from the Koidu Kimberlite Project are transported under guard of independent security contractor (Group 4 Securicor) to the Government Diamond and Gold Office (GGDO) in Freetown, where they are valued by the GGDO valuator, as well as the independent government valuator.
Koidu Holdings is committed to Diamond Best Practice Principles. Our diamonds have been produced from legitimate sources not involved in funding conflict and in compliance with United Nations Resolutions. Sierra Leone became a member of the Kimberly Process in 2003.
What is the Kimberley Process?
The Kimberley Process (KP) is a joint governments, industry and civil society initiative to stem the flow of conflict diamonds - rough diamonds used by rebel movements to finance wars against legitimate governments. The trade in these illicit stones has fuelled decades of devastating conflicts in countries such as Angola, Cote d'Ivoire, the Democratic Republic of the Congo and Sierra Leone.
The Kimberley Process Certification Scheme (KPCS) imposes extensive requirements on its members to enable them to certify shipments of rough diamonds as 'conflict-free'. As of September 2007, the KP has 48 members, representing 74 countries, with the European Community and its Member States counting as an individual participant
How does the Kimberley Process work?
The Kimberley Process Certification Scheme (KPCS) imposes extensive requirements on its members to enable them to certify shipments of rough diamonds as 'conflict-free' and prevent conflict diamonds from entering the legitimate trade. Under the terms of the KPCS, participating states must meet 'minimum requirements' and must put in place national legislation and institutions; export, import and internal controls; and also commit to transparency and the exchange of statistical data. Participants can only legally trade with other participants who have also met the minimum requirements of the scheme, and international shipments of rough diamonds must be accompanied by a KP certificate guaranteeing that they are conflict-free.
Marketing, cutting and polishing
Koidu Holdings markets its production through the Steinmetz Diamond Group.
When diamonds reach the Steinmetz facilities, they are boiled in acid, then sized and sorted according to their shape, color and purity and priced for sale to an international clientele, or sent for cutting and polishing. With seven decades of expertise in the diamond industry, Steinmetz has interests ranging from cutting, polishing, manufacturing jewellery and retail. Known for its unique approach to marketing, the Group has promoted the glamour of diamonds at various high-profile events, such as the Oscars, the Baftas, the Smithsonian Institute, Natural History Museum, and the Monaco Grand Prix.
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 Above: Steinmetz specializes in the cutting, polishing and marketing of especially large and extremely rare stones.
 Right: Diamond-studded Steinmetz Monaco Grand Prix Trophy |
The Steinmetz Group has state-of-the-art cutting and polishing factories in New York, Johannesburg (South Africa), Windhoek (Namibia), and Gaborone (Botswana), as well as offices in Antwerp, London, Tel Aviv, Bombay, Chicago, and Geneva.
Steinmetz is a world leader in the trading of rough diamonds (over $1.4 billion annual turnover) and has a unique relationship with De Beers, being the leading DTC Sightholder. Steinmetz recently invested $9 million in a diamond polishing facility in the Diamond Technology Park in Gaborone, specifically to beneficiate diamonds produced in Botswana. After South Africa and Namibia, this is another Steinmetz step towards realizing its vision to beneficiate in the country of origin so that the local economies may reap the benefits.
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Above:
Steinmetz -Jeweller to the Stars
Right: The Steinmetz Pink - Originated in southern Africa, and purchased from De Beers, the Spectacular 59.6 carat, oval cut is a Type IIA stone. A stone of this nature is relatively rare and is officially priceless. |
Sotheby's Diamonds, is a unique partnership between the world's oldest auction house and the Steinmetz Diamond Group, the expert in sourcing and cutting extraordinary diamonds, With a focus on exquisite stones and custom pieces, this luxury retail venture makes the acquisition of fine jewellery even more attractive. Some of the famous diamonds created by Steinmetz are the 203.04 carat, internally flawless De Beers Millennium Star, and the Steinmetz Pink a 59.60 carat, flawless vivid pink diamond.
Lior Levin, C.E.O Sotheby's Diamonds:
"Sotheby's Diamonds values the supply of rare gems from the Koidu mine through Sotheby's joint venture partnership with the Steinmetz Diamond Group; we are very proud to offer these important diamonds to our discerning international clientele."
