A Diamond in the Rough
April 1, 2006
Just 200 km (124 miles) south of the Arctic Circle, Canada's Ekati Diamond Mine, operated by BHP Billiton Diamonds Inc., is one of only two diamond mines operating in North America and the first to combine open-pit and underground mining. Its first diamond was recovered in October 1998. Today, the mine processes more than 10,000 tons of ore per day, producing four to five million carats of rough, gem-quality diamonds each year. This represents nearly 4 percent of current world diamond production by weight and 6 percent by value. But it doesn't come easily.
Think Big-And ToughThe Ekati Diamond Mine site covers 344,000 hectares of continuous permafrost (permanently frozen subsoil) about 300 km (186 miles) northeast of Yellowknife-the diamond capital of North America located in Canada's Northwest Territories. Vehicle access to the site is possible only during an eight- to 12-week period via an ice road rebuilt every winter over frozen lakes and tundra. During this brief period, trucks bring in the big machinery and other bulky freight needed during the year. Everything else, including employees, is flown in year-round.
A virtual self-contained city in the wilderness, the Ekati Diamond Mine provides living and support facilities for nearly 700 people, plus the extensive infrastructure necessary for mining and ore processing operations. New construction is continually underway to support additional mining locations at new kimberlite pipes (see sidebar on page 46).
BHP Billiton's extensive engineering department includes three surveyors who work above ground and four who work underground (although they can work interchangeably depending on the need). According to Senior Mine Surveyor Kevin Hutchinson, surveyors are among the first on site at a potential new mine and among the last to leave. Hutchinson has worked primarily above ground at the mine since 1995. From working with the geologists to help determine potential new mining locations, to providing as-builts for final reclamation work, surveyors provide a critical service at every stage in the diamond mining process-at every level of the mine.
But working in the sub-Arctic is no walk in the park. Wind chill can drive winter temperatures below -60o C (-76o F). With such extreme working conditions, the mine mandates rigorous safety-first policies. "If an individual feels a particular location is too cold or dangerous to work, he has the "right to refuse' that job," Hutchinson says. "We also leave our trucks running while we're in an active mining area and often can work outside for only a few minutes before jumping back in the truck to warm up."
Above-ground MiningAbove-ground control for the overall site was established in 1995 using conventional surveying instruments. The GPS grid was tied in more recently. The mine uses WGS84 as well as the UTM system, 12 North. To bring surface control to each new underground mine, surveyors traverse down the portal ramp, continually putting control points up on the "back" (ceiling) of the mine.
At any potential new mine location, surveyors, geologists and drilling crews work together to determine the location and extent of the ore-bearing kimberlite by drilling test holes to obtain samples. Once drilled, surveyors again as-built the holes to provide precise location information to mine engineers, who then prepare computerized models of the ore body. Core samples are analyzed to determine the ore/waste rock contact; these stats help them accurately map out each new mine. Once a new mine model is created, surveyors lay out the mine according to design. The map is generated by Maptek (Lakewood, Colo.) VULCAN 3D modeling and mine planning software.
In most cases, when a kimberlite pipe is initially exploited, above-ground, open-pit mining is conducted. Large hydraulic shovels load the ore into trucks, which take it to the processing facility. As the pit gets progressively deeper, surveyors provide constant support to the drill and blast crews. After this method has exhausted the readily available ore, underground mining begins if deemed profitable. Extensive sample drilling, careful analysis of the core samples and plenty of practical geology and engineering effort go into the crucial decision of whether, and how far, to go underground. Once underground mining starts, all surveying tasks-whether above or underground-are performed by the underground crew. The above-ground crew then moves on to the next open pit.
Surveying in the PitThe Ekati site encompasses multiple potential mines. To date, some 150 kimberlite pipes have been discovered on the claim block; however, not all contain economically recoverable diamonds. The Panda pit was the first open-pit mine developed at Ekati. Panda's open-pit ore production started in August 1998; underground production began in early 2005. The pit is 800 m (1/2 mile) in diameter and 300 m (984 ft) deep. The underground mine depth is expected to extend approximately 200 m (656 ft) below the pit bottom.
To facilitate real-time kinematic (RTK) GPS surveying, a Trimble (Sunnyvale, Calif.) 5700 GPS system was installed as a base station in the nearby truck shop. The base station uses a Trimble TRIMMARK III radio to communicate with rovers working throughout the above-ground area and in the pit.
The above-ground survey crew uses two Trimble 5800 GPS systems as rovers and two Trimble S6 total stations. All the systems use the Trimble TSC2 controller, which enables seamless data transfer to and from the office and between units. The controller's color display remains bright and easy to see even in cold temperatures, which is essential for this environment.
Of critical importance to the surveyors is the ability to effortlessly switch between GPS and optical systems, according to Hutch-inson. "It's really easy to start the job using one system and finish it using another," he says. "We don't need to convert any data or use a disk to share data; the systems communicate with each other through the controller." By using the same controller, survey data is seamlessly integrated in a single file.
Most work is done with the GPS systems; the total stations are used primarily in locations where GPS satellite coverage is limited, such as the inside edges of the pit ramp and benches. Points along these edges are surveyed to define the crests and toes, which become the basis for the continuously evolving pit shell map.
Open-pit surveyors also use the total station's direct reflex (reflectorless) capabilities to get important data by "scanning" or taking continuous measurements of pit walls to pick up any slip planes or fault structures that may be going through the rock. This helps the mine's geotechnical engineers determine how the faults will impact the pit walls at lower depths.
"Pit design is done before we get to this point," Hutchinson says. "But as the engineers come across the fault structures, we pick them up and the engineers digitally build them into their computerized designs." They then may redesign parts of the mine-or drill anchors to hold the rock safely together.
"Without direct reflex, at best we'd get a shot at the bottom and they'd have to use a compass to measure up the wall," he says. "But now we can shoot 20 shots running along it from up to 400 meters away, gaining an accurate picture of what the fault structure is doing."
At the end of each shift, both pit and underground crews download the data from their controllers to Trimble Geomatics Office software for post-processing. The data is then electronically transferred to the VULCAN software to update the overall mine design. Applicable updated design data is reloaded into the controllers at the start of each new shift.
Underground MiningKoala North, opened in early 2002, is the first underground diamond mine in North America. In addition to producing diamonds, Koala North served as a test mine to establish what types of equipment, materials and processes work best in sub-Arctic permafrost conditions.
The mine uses an "open benching" method. A decline ramp is mined in the waste rock alongside the kimberlite pipe. At various levels (typically 20 m/66 ft apart vertically), an access tunnel and three parallel tunnels, or "drifts," are mined through the pipe. Each drift is approximately 5.5 m (18 ft) high by 5.5 m (18 ft) wide where it runs through granite, but somewhat smaller in the softer kimberlite. The drifts can be up to 150 m (492 ft) long at the upper levels, but are progressively shorter as the kimberlite "carrot" narrows.
Starting at the far end of each drift, blast holes are drilled upward into the bench above. Sections are progressively blasted off the bench. The blasted ore is dug out and loaded directly onto low-profile haul trucks, which take the ore to the surface or to a storage area.
Surveying Safer in the DarkIt's dark down in the drifts; vehicle lights and miners' lights provide the only illumination. The underground survey team uses a Trimble S6 total station and a Trimble 5600 total station for backup. The total stations provide robotic operation and remote control capability so that a single surveyor can make rapid measurements even in low-light or no-light environments.
"The big difference between above-ground and underground surveying is that underground, you set up under the point to make your measurements," says underground surveyor Darin Bettiol. Survey control points are marked with spads (horseshoe nails) in the roof of the drift (called the "back") and/or in the walls, so they will not be damaged by the frequent vehicular traffic. Using cherry-picker baskets from their trucks, surveyors hang a wire and plumb bob from the spad and center it over the total station. They can also set new stations without climbing back down; they simply operate the Trimble S6 total station "robotically,' i.e., remotely from the controller.
Topos of the walls, back and floor (sill) and other measurements are done with the Trimble S6 operating in direct reflex mode for both safety and practicality. The laser is readily visible in the dark, which allows the surveyor to take fast, accurate topos. Advancing the underground control points is done with the Trimble S6 operating with a prism for optimal accuracy. The laser is pointed at the prism, the Autolock feature is turned on and the instrument automatically locks onto the prism and measures the point.
Underground surveyors find the S6 robotic capability essential, according to Bettiol. Along with setting up new stations, they are able to walk along the wall beside the laser beam, checking for breaks or faults in the wall they might not otherwise see from 30-40 m away.
"We can now do many of our jobs with just one surveyor running the instrument remotely," Bettiol says. "We used to have to use two people for everything, but with the S6 we don't have to have someone at the instrument-and a lot of times operating remotely is a lot safer down here."
Technology Aids EfficiencyTo establish the long-hole drilling locations for the blasting charges, surveyors use a 14-ft paint stick to mark numbered vertical lines on both walls at eye level that run perpendicular to the drift. They control the total station robotically with its controller using the S6's "turn-to" and joystick remote capabilities.
The drilling machine uses lasers to align with the reference marks. The drilling department determines the position, depth and "spread" of the blasting holes for a given location and has loaded the drilling layout into the machine's control unit. After the machine has drilled the holes to the required depths (up to 15 m or 49 ft), the surveyor as-builts their positions.
Surveyors can also upload the mine design for each level into the controller as a background file. When doing actual measurements, they can then display all shots on the map to see if there are any problems in direction or location, and correct the drill operator before the next cut.
"We used to have to go up to the office, load our data into AutoCAD and draft the survey we just did underground," Bettiol says. "They'd be waiting underground to find out if they were still on plan; we'd then go back down or radio directions. Now as soon as we take a shot, it shows up on the controller map and we can give real-time direction to the drillers immediately. It makes a huge difference in time and productivity."
One of the prime concerns in mine surveying, both above and below ground, is the possibility of a drill hitting a "bootleg"-the bottom of a previously drilled and set hole in which the charge has not detonated. This has never happened at Ekati, and careful surveying is one of the main reasons for its good record. The job demands constant care and attention, and the surveyors point to Ekati's "safety first" policies that have kept the mine safe since it was discovered.
So the next time you think about giving a diamond to your loved one, remember the tremendous effort it has taken to bring that piece of cold fire to life. Neither mining-nor giving-a diamond is a trivial matter.
SIDEBAR: Looking for Carrots-and Carats-in the TundraThe diamonds recovered today at the Ekati Diamond Mine were formed some three billion years ago. Extremely high temperatures and intense pressures caused pure carbon to crystallize into diamonds 150-200 miles deep in the earth's crust.
Some 50-70 million years ago, volcanic eruptions brought molten kimberlite rock, containing the diamonds and other minerals, to the surface. The eruptions blew off the top 200-400 meters (656-1312 ft) of granite to create small craters. The kimberlite eventually hardened into carrot-shaped "pipes" beneath the craters. The volcanic debris sealed the kimberlite pipes from air and water. Over time, the debris compressed to form small lakes.
"Kimberlite" is named for Kimberley, South Africa, where such pipes were first discovered in the 1870s. Diamonds are mined today in about 25 countries, on every continent except Europe and Antarctica.
Most miners long thought finding diamonds in the Canadian north was impossible-except for geologist Charles Fipke. Beginning in 1981, Fipke scoured the tundra for indications of kimberlite. After 10 years, Fipke and fellow geologist Dr. Stewart Blusson found their "lode" in the Canadian Northwest Territories. In 1991, with BHP Billiton geophysicists, they discovered the first kimberlite pipe below Point Lake, near the present mine site. The discovery started one of the largest staking rushes in Canadian mining history.