Diavik Diamond Mine

The Diavik Diamond Mine is Canada’s second largest diamond mine. It is located on East Island in Lac de Gras, 186 miles (300 km) northeast of Yellowknife in the Yukon Territory. Since the 1990s the mine has included both open-pit and underground mining methods and is jointly owned by Diavak Diamond Mines Inc. and Aber Diamond Mines Ltd. Diavik—both Canadian companies headquartered in Yellowknife. Diavik Diamond Mines Inc. is also a wholly owned subsidiary of Rio Tinto plc of London—the owner of the Argyle Diamond Mine in Australia, which is one of the world’s largest diamond-producing mines.

According to a 1999 feasibility study, the approximate life span of the mine is expected to be 16 to 22 years.^[1] The mine has a footprint of four square miles (10 km²) with reserves stored in three central diamond ore bodies otherwise known as kimberlite pipes—A154 North, A154 South, and A418.^[2] These pipes are considered quite small compared to the world average, but contain quite high-quality diamonds. About two million tons of ore is removed from the mine annually. In 2008, the mine produced about nine million carats of diamonds.^[3]

The construction of the Diavik Diamond Mine presented a unique challenge since the overlying water of Lac de Gras had to be removed to gain access to the diamond ore bodies. This was achieved by building specially engineered rockfill dams that completely encircled the kimberlite pipes so the water could be drained from inside. About $1.3 billion was allocated for the mine’s initial construction in 2001. An estimated CA$4 billion has been spent on construction and mine operations since the mine's completion in December 2003.^[4]

In 2007 an announcement was made by Rio Tinto and Harry Winston Diamond Corp. that all operations would be taken completely underground by 2009, extending the life of the mine past 2020.^[5]

[edit] History

[edit] Early Exploration

In 1991 Aber Resources staked mineral claims at Lake de Gras, sparking diamond exploration in the area. By June 1992 Aber Resources had teamed up with Kennecott Canada Exploration to form the Diavik Joint Venture. Over the next three years, exploration would result in the discovery of four diamond-bearing pipes—A21, A154 North, A154 South and A418.

[edit] Bulk Sampling

In February 1996 of the following year an exploration camp of 75 people was established at Lac de Gras to begin underground bulk sampling. The sampling of approximately 5,900 tons of ore from A418 and A154 South was completed by July, prompting Diavik Diamond Mines to establish a head office in Yellowknife.^[6] In March 1997 bulk samples from the mine were transported to Yellowknife for processing and about 21,000 carats of diamonds were recovered. By the end of the year, both environmental baseline studies and pre-feasibility studies were completed; in September 2000 the Diavik Joint Venture received the necessary Federal government approval to move ahead with construction of an open-pit mine and begin production.^[7]

[edit] Construction of the A154 Dyke

Construction on the mine began in January 2003. The biggest obstacle in constructing an open-pit mine was the building of a special rockfill dam. The dyke was built around the A154 kimberlite pipe. Once the dyke was built, the water needed to be drained from inside to access the kimberlite pipes that lay underneath. All the fish inside the lake also had to be removed without harm. Another major challenge was building the dyke without contaminating the water supply on the outside parameter of the dyke. Approximately four million tons of rock varying in size was used to build the 2.4-mile (3.9-km) dam.^[8] Another two million tons of rock was used to complete the dyke cap and toe berm. The water control system consisted of a grout curtain in conjunction with a plastic cut-off-wall and overlapping jet grout columns. The dyke also featured refrigeration systems called thermosyphons to maintain permafrost levels installed at points where it crossed islands. The thermosyphons operated in a passive mode in winter and active refrigeration mode during the summer. Sensors placed throughout the dyke were also were used to monitor and measure temperature, pressure, and movement.

After a process of detwatering, the A145 dyke was made watertight by July 2002 and pumped dry. The sediment and glacial till at the bottom of the lakebed had to be stripped as the water level dropped. With a height of 33 feet (10 m) and a maximum depth of 92 feet (28 m), the A154 dyke received Canada’s highest award for engineering excellence from the Canadian Council of Professional Engineers.^[9]

[edit] Construction of the A148 Dyke

By summer 2005 construction on a second dyke connecting to A154 was underway. The methods used to construct the dam were similar to A154, but A148 was only 1.3 miles (2.1 km) long and built in water up to 105 feet (32 m) deep.^[10] Rock from the A154 pit was used and crushed on-site with the assistance of a crushing facility. The A148 dyke was completely water tight by 2006.

[edit] Mine Infrastructure

The Diavik Diamond Mine’s infrastructure covers all aspects of mine operation. The mine features an on-site processing plant as well as a power plant to service heavy equipment, fuel tanks, a boiler plant, and administrative and accommodation buildings for workers. Since the mine is located in a remote area, it also features its own airstrip designed to accept commercial aircraft from Boeing 737 jets to Hercules transport aircraft. Workers and supplies are flown in and out of the mine on a regular basis.

[edit] Open-pit Operations

Mining of the three kimberlite pipes at Diavik has been conducted primarily through open-pit methods since the mine began producing diamonds in 2003. Open-pit mining at Diavik has produced more than 35 million carats of diamonds.^[11] As of 2006 open-pit operations had been exhausted at the A154 North pipe, while surface mining was still being carried out at the A154 South pipe. As each pit is dug deeper, its width increases. The dyke walls encircling each pit pose a limit as to how big they can become. In addition, extending the dyke walls out into the lake jto support ongoing open-pit operations would not be considered very cost-effective.

[edit] Ore Processing

Once ore is removed, it gets transported by haul trucks to Diavik’s on-site processing plant. The plant features a run-of-mine building connected to a Dense Medium Separation (DMS) plant. Another recovery building is used to remove the diamonds from the host kimberlite rock. Gravity-based methods are used to process the ore. Ore first gets trucked to a storage facility outside the processing plant. Primary crushing equipment is used to crush down the ore before it enters the processing plant. It is then mixed with water and crushed down to less than 1.2 inches (3 cm).^[12] The mixture is conveyed to a dense medium separation circuit where a fine-grained sand mixture known as magnetic ferro-silicon (FeSi) gets added to the crushed down ore and water. The Fesi enhances the gravity effect of diamond and other heavy mineral separation. A magnet is used to capture the FeSi mixture that is saved and re-used. Water used in the process also gets recycled. The less heavy waste kimberlite is directed to the Processed Kimberlite Containment (PKC) area where it gets permanently stored. The heavier diamond mineral concentrate is conveyed further along to a recovery circuit.

[edit] Diamond Extraction

Diamonds are recovered from the heavy waste minerals in a recovery building using x-ray technology. Under x-ray light, diamonds react by glowing. Using strategically placed photo-electric sensors, blasts of air blow the diamonds off the conveyor belt into collection plates. The remaining waste minerals are reprocessed and directed to the PKC. The diamonds are then shipped to Yellowknife for cleaning, royalty evaluation, and division amongst the owners.

[edit] Equipment Used

• Backhoe
• Blasthole drill
• Boom truck
• Bulldozer
• Continuous miner
• Crane
• Excavator
• Float truck
• Front end loader
• Grader
• Haul truck
• Hydraulic excavator
• Mine truck
• Packer
• Roadheader
• Rock drill
• Scoop tram
• Wheel loader

[edit] Refurbishment/Renovations/Recent Projects

In 2007, Rio Tinto, in partnership with Harry Winston Diamond Corp., made a significant investment of US $800 million to build an underground mine at Diavik. Construction of the underground mine began with the development of tunnel with a 9,514-foot (2,900-m) decline.^[13]

Converting the mine from a surface operation to underground will be costly. The construction of an underground mine involves digging out kilometers of tunnels and building supporting infrastructure. Once converted, the underground mining operations will use cut-and-fill and blasthole stoping methods. Cut-and-fill stoping involves using mining machines such as a continuous miner to cut the ore into long panels. Blasthole stoping involves using drills and explosives to break down the ore into taller panels. Once removed the ore is transported through a vertical tunnel and loaded into haul trucks where it is delivered up to the surface. The mined-out stopes then get backfilled using cemented paste or crushed waste rock.

The transition from an open-pit mine to an underground mine will also require upgrades and improvements to existing infrastructure as well as the purchase of new underground mining equipment. One option being explored over the conventional drill-and-blast method is the use of road headers—a bulldozer type vehicle with a large revolving drum mounted on an arm at the front of the machine. Used quite often in coal mining, the drum on a road header features tungsten carbide teeth that cut into the diamond bearing kimberlite.

Completion of the underground mine is set for early 2009 and will extend the mine’s life to 2020. The mine will have three open pits and four underground mining areas operating. Not all open-pit areas will be mined concurrently. A fourth kimberlite pipe known as A21, located 1.9 miles (3 km) away from the three other pipes, is being assessed for its potential for both open-pit and underground mining. The last open-pit operation is expected to be phased out by 2016.^[14]

[edit] References

1. ↑ Diavik Diamond Mine Fact Book. Rio Tinto
2. ↑ The Diavik Diamond Mine. Rio Tinto Diamonds website. 11-03-2009.
3. ↑ Diavik Diamond Mine Fact Book. Rio Tinto
4. ↑ Diavik Diamond Mine Fact Book. Rio Tinto.
5. ↑ Mining: Our Operations. Diavik Diamond Mine Official website. 11-03-09.
6. ↑ History. Our Operations. Diavik Diamond Mine Official website. 11-03-2009.
7. ↑ History. Our Operations. Diavik Diamond Mine Official website. 11-03-2009.
8. ↑ July grand opening for Diavik mine. Northern News Service online. 11-03-2009.
9. ↑ Dikes. Our Operations. Diavik Diamond Mine Official website. 11-03-2009.
10. ↑ Diavik Diamond Mine Fact Book. Rio Tinto.
11. ↑ Diavik diamond mine in N.W.T. gets new development money. CBC News. 11-03-2009.
12. ↑ Processing. Our Operations. Diavik Diamond Official website. 11-03-09
13. ↑ Mining. Our Operations. Diavik Diamond Mine. 11-03-2009.
14. ↑ Diavik goes Underground. Annual Review 2006. Rio Tinto website. 11-03-2009.

[edit] External Links

• Diavik Diamond Mine Official website