Overview
The Diavik Diamond Mine is located on a 20 square kilometre island, informally called East Island, in Lac de Gras, approximately 300 kilometres by air northeast of Yellowknife, capital of Canada's Northwest Territories. The Arctic Circle lies 220 kilometres north of the mine.
Diamonds were first discovered in the Lac de Gras region in the early 1990s, and construction of the Diavik Diamond Mine completed in 2003. The mine, which has a current footprint of approximately 10 square kilometres, is projected to produce approximately 110 million carats of diamonds over its mine life of 16 to 22 years, with an expected annual diamond production peak of approximately 10 million carats.
Location
The Diavik Diamond Mine is located in one of the most remote and forbidding places in the world - 220 kilometres south of the Arctic Circle and on the bed of a vast northern lake, Lac de Gras.
A single road, built out of ice and crossing frozen lakes, connects the mine with other operations and Yellowknife, capital of the Canada's Northwest Territories.
The construction of an open pit mine and its infrastructure is an engineering feat on a grand scale, with the creation of 3.9 kilometre rockfill dike to hold the frigid waters of Lac de Gras at bay. Not only did the extremely harsh climatic conditions present significant construction challenges, but nothing was allowed to blemish the pristine waters of the lake during its building.
Geology
The Diavik Diamond Mine is located in Precambrian rocks of the Slave Geological Province. This ancient rock was formed about 2.7 to 2.5 billion years ago and is among the world's oldest geological structures. The Slave Geological Province is known to host deposits of gold, copper, zinc and diamonds, and has produced much of the North's mineral wealth.
Diavik's diamonds are forged by intense heat and pressure deep within the earth of the arctic north. 55 million years ago, volcanic activity injected kimberlite magma towards the surface, bringing with it diamond bearing ore and forming the kimberlite pipes which are today mined for its precious ore.
Kimberlites are the roots of small and ancient volcanoes and are a common means by which diamonds are brought to the surface of the earth. The Diavik Diamond pipes range in surface area from 0.9 to 1.6 hectares and extend well below 400 meters below the surface. As an indication of the rarity of diamond-bearing kimberlite, only 23 of the 5,000 kimberlites found in the world contain enough diamonds to mine.
This property is located near Lac de Gras in the central part of the Slave Structural Province which forms a distinct cratonic block within the Canadian Precambrian Shield containing deformed and metamorphosed, Archean aged metaturbidite and lesser metavolcanic rocks of the Yellowknife Supergroup.These supracrustal rocks have been intruded by extensive Archean granitoids, and are in turn intruded by undeformed, late Archean granites and diabase dike swarms. Pleistocene continental glaciation and retreat has left a thin, discontinuous mantle of sandy and bouldery basal and ablation tills and ice contact deposits such as eskers in the area.
Mining & Operation
Diavik currently mines three diamond-bearing ore bodies known as kimberlite pipes using a combination of open pit and underground mining methods.
The Diavik property consists of a total of 273,966 ha of prospective lands surrounding the Diavik mine site, located about 300 km northeast of Yellowknife and anout 30 km southeast of the Ekati Diamond Mine. The land package consists of 236 mining leases and 55 mineral claims.
Diavik is at a major milestone in its mine life. By 2012, the mine will change from an open-pit mine to an all underground mine which will require different mining methods, skills, equipment, and additional supporting infrastructure. For a short time, the mine will be operated in both open-pit and underground mines concurrently. Going underground assures a mine life of 16 to 22 years.
An open pit mine gives Diavik access to the diamond-bearing kimberlite ore beneath Lac de Gras. Diavik mines three kimberlite pipes, called A154 North, A154 South and A418 by open pit mining methods. A fourth pipe, A21, was bulk sampled in 2007 to assess whether it should be included in the reserve.
Along with open pit mining, all three kimberlite pipes will eventually also be mined from underground. Diavik expects that the transition to total underground mining of the pipes will be completed around 2012. In order to determine how best to proceed with underground mining, Diavik is conducting test mining of the two richer ore bodies: A418 and A154 North, with plans to undertake underground mining of the A418 pipe as part of Diavik Phase 2. Approximately 2,900 meters of the main decline tunnel for underground mining has been completed, with another 500 meters required prior to completion.
Conventional truckand-shovel open pit mining is used to mine the upper portions of the pipes to their economic depths, whereupon underground mining will be used to continue mining. The first open pit began prestripping in autumn 2002, reached sustainable production rates at the start of 2003, and is expected to be finished before 2009. This pit provides access to two pipes. A second open pit for the third pipe began pre-stripping at the end of 2006, is expected to reach sustainable ore production capability in the second half of 2008, and is expected to operate until the end of 2011. Underground mine development is well advanced for expected production in 2009. The underground mine plan is based on underhand cut and fill mining using continuous mining machines and, in harder kimberlite zones, conventional blast hole stoping with backfill. There is expected to be a three-year transition period during which open pit mining will taper off as underground mining ramps up.
The underground mining will use a combination of underhand cut-and-fill mining (with average life-of-mine mining costs of approximately Cdn$90 per tonne) and blast-hole stoping (with average life-of-mine mining costs of approximately Cdn$66 per tonne) depending on the rock stability encountered in actual production. Estimates are for the majority of the underground mining to be cut-and-fill but work currently underway is showing that there is an opportunity to improve on this. In comparison, average mining costs for open pit are expected to be approximately Cdn$53 per tonne of ore mined over the remaining life of the open pit.
Processing
The Diavik Diamond Mine processes up to 2 million tonnes of ore annually.
Separating diamonds from the kimberlite host rock is a non-chemical, gravity-based process which relies on the diamonds' heavier weight to separate them from waste rock.
At the beginning of this process, diamond-bearing kimberlite ore is trucked to a storage area outside the process plant. A primary sizer reduces the ore before it enters the plant where it is mixed with water and crushed to less than 30 millimetres. The ore is then conveyed to the dense medium separation circuit. Here fine grained, heavy and magnetic ferro-silicon (FeSi) sand is added to the crushed ore and water mixture. The FeSi magnifies the gravity effect and enhances diamond and other heavy mineral separation. A large magnet recovers the FeSi, which is recycled. Water is also recycled.
The less dense waste kimberlite fraction is directed to the processed kimberlite containment (PKC) area for permanent storage. The heavy mineral concentrate (containing diamonds, garnet, diopside, olivine, and spinel) is conveyed to the recovery circuit.
In the recovery building, the diamonds are separated from the waste heavy minerals using X-rays to trigger a unique characteristic of diamonds. Diamonds glow under this kind of light, and photo-electric sensors direct strategically placed air blasts to blow the diamonds off the conveyor belt into diamond collection receptacles. Waste minerals are reprocessed and directed to the PKC. The diamonds are then shipped to the Diavik product splitting facility in Yellowknife where they are cleaned using chemicals, divided 60/40 between the joint venture partners (Rio Tinto and Harry Winston), and undergo evaluation, for government royalty purposes.
Despite being a high grade deposit, the diamonds represent approximately one part per million of the host kimberlite rock. Once this small fraction of diamonds is removed, the remaining kimberlite is placed in the Processed Kimberlite Containment area (PKC). Constructed in a natural valley in the centre of East Island, the PKC is bounded by dams constructed at either end.
At the completion of mining, this PKC area will be approximately 1 kilometre long and 1.3 kilometres wide and contain up to 40 metres of processed kimberlite. The PKC will be covered with waste rock to seal it safely forever.
