Huge B.C. mine has own style

The very large, very low grade Highland Valley Copper (HVC) mining complex in south-central British Columbia is not only Canada’s largest metal mine, but is also globally significant. In 2004 it produced 1.4% of the world’s copper and 3% of the world’s molybdenum. HVC is 97.5%-owner Teck Cominco’s only metal mine in the province.

Making such an operation profitable has required a large mining fleet, an efficient high-capacity conveying system, cutting-edge technology, and a focus on training the excellent workforce. In fact, without the application of state-of-the-art technologies, it would not have been possible to mine at a profit, says HVC president and general manager Wolf Nickel.

The success is evident. Over the last 10 years HVC has produced about 350 million lb of copper per year plus between 3 and 10 million lb of molybdenum. It has earned money in 17 of the last 20 years, financing all capital and operating spending from cash flow.

Last year was a record year for both production and profitability at HVC. Three pits fed 50.7 million tonnes of ore (138,800 tonnes/ day) to the plant, which produced 179.0 tonnes (382 million lb) of copper and 6.3 million lb of molybdenum in concentrate. HVC generated $613 million in operating profit in 2005, up from $431 million the previous year due to higher metal prices and increased copper sales.

Mining innovations

The ore in the deepening pits is getting harder. The Lornex and Valley pits continue to be mined, and the Highmont pit reopened last year after 20 years of inactivity, in response to the rise in moly prices. The Lornex deposit is moly-rich, with copper primarily in chalcopyrite. The Valley pit largely yields bornite, with low moly values, from ore that is more competent and less structurally altered than at Lornex. Highmont was actually a moly mine with the highest moly and lowest copper grades of the three pits.

Mine modeling uses Gemcom software, defining every 25-m x 25-m x 15-m block according to grade, rock and structure.

Drilling is done by three Bucyrus Erie 49-R rotary electric drills that drill 311-mm-diam blastholes to a depth of 16.5 m, allowing for 15-m bench heights. The predominantly wet conditions require HVC to mix its own Anfo emulsion (under licence from Dyno Nobel) for blasting, made from liquid ammonium treated with an emulsion agent. This is much more water-resistant, with improved sensitivity and more energy, giving a more efficient blast. HVC uses about 20 million kg of emulsion per year.

Improved co-ordination between the departments and the application of leading-edge technology over the last decade have enabled the mine to provide the mill (its “customer”) with a more consistent product, and cut overall costs. Previously each department was trying to minimize its own costs, but the result was plant feed with variable hardness. All surveying is done using GPS now. GPS on the production drills and Aquila software allows the location and ore hardness to be determined during drilling. This extra information is worth the extra time it takes to drill a production hole, which has gone from 25 to 42 minutes. WipFrag at the crusher measures ore fragmentation, allowing blasts to be engineered to maximize fines production.

Since shovels are equipped with GPS and automatic weighing, shovel operators know exactly the kind of blasted material they are loading into the dispatch-controlled haul trucks. Ore is trucked to one of three 20-million-tonne-capacity gyratory crushers — two in the Valley pit and one stationary crusher in the Lornex pit — and reduced to -15-cm. From the Valley pit it is conveyed by the two-belt, 1.8-m-wide high-capacity system to one of three coarse ore stockpiles outside the plant. The ore can be carefully blended to give the mill a constant metal content and hardness.

Since 1990, the mine has used a dispatch system to monitor and control the whole operation up to the plant, but it does more. Maintenance records and operational data are tied in; HVC will soon upgrade to a GPS-based dispatch system.

Highland Valley Copper is one of the first mines to use several computerized theodolites reading 500 prisms and stations for real-time monitoring of the wall slope stability in the pits. Any movement triggers an alarm in the dispatch centre. This tool enhances both safety and productivity, so mining can be done right up to the design slopes with confidence.

Processing and tailings

The nominal capacity of the mill is 133,000 tonnes/day, but it has exceeded 160,000 tonnes/day in softer rock. While the grade is low, the ore is relatively free of contaminants such as arsenic. Moly has become a very important revenue source, increasing from <5% to approximately 20% of HVC’s revenues in 2005. Since 2004 the focus has been on improving molybdenum recoveries, which have risen from 50% to 62%.

The plant retains much of the layout and the original equipment from the two plants that were joined in 1988. The Lornex end has three SAG mills that each feed two ball mills, and the Highmont end has two autogenous mills that each feed two ball mills. SAG mill C grinds about 30% of the plant’s feed.

Cyclone overflow from the ball mills at each end of the plant feeds separate bulk (Mo and Cu) flotation circuits of Denver rougher and scavenger cells. After cleaning, regrind and recleaning, the bulk concentrates from both ends are combined and advance to the copper-molybdenum separation circuit. Lime is added to the tailings slurry to help it flow to the tailings impoundment.

In the Cu-Mo separation circuit, depression of the copper and flotation of the molybdenum results in copper “tails” and molybdenum sulphide concentrate. The flotation of the molybdenum is challenging as the plant tries to achieve high recoveries while minimizing copper content in the moly concentrate. These cells are enclosed because of the potential danger involved in generating hydrogen sulphide in the process. The two banks of moly cells will be replaced with new Outokumpu equipment by the end of August.

The “tails” from this circuit is really the copper concentrate, which is sent for dewatering in a thickener. Its underflow feeds two seven-disc Dorr-Oliver-Long filters, which reduce the moisture content to 12%. This is further reduced to <8% moisture in a natural gas-fired rotary dryer and conveyed to a storage silo. The silo loads copper concentrate into trucks that take it 50 km to a railhead in Ashcroft, from which 80% is railed by CP Rail 300 km to Vancouver Wharves for shipment to Asia, and the rest is railed by CN to smelters in western or eastern Canada.

A leach plant uses the Brenda process to improve molybdenum recovery. The moly concentrate is leached with ferric chloride in glass-lined, steam-jacketed reactors for an hour at 105C and 135 kPa pressure. This process removes up to 3% Cu from the moly concentrate, leaving <0.25% Cu. (Metallic copper is recovered from the leach solution by precipitation.) The cooled slurry is filter-pressed and fed to a furnace for drying to 5% moisture. The molybdenum concentrate is bagged in 1.8-tonne tote bags and trucked to customers.

The tailing slurry flows by gravity 7 km from the mill to the HH dam, at the upstream end of the 2-km-wide x 10-km-long (11,000-ha) tailings impoundment, where the tails disperse over the surface. The LL (downstream) dam — 2.5 km long and 145 m tall with a till core centre-line construction — is one of the larger compacted, earth-fill tailings dam structures in Canada, using cycloned coarse tailings as construction material. It was designed to withstand maximum credible earthquakes and a 1-in-10,000-year flooding event. The dam’s engineering benefits from management by HVC’s own dam expert, civil engineer Dal Scott.

The tails are essentially sand with some clay. A huge volume of working water is needed to keep the tails underwater and unfrozen in winter. The high pH (9-10) of the water — due to the basic host rock, its contained ca
rbonates plus added lime — buffers the small pyrite content, so the tailings have no acid-generating potential.

Water is contained within the site, and there is no need for treatment. Water collecting in a seepage pool below the LL dam is returned to the tailings pond where barges reclaim water to the reservoir that feeds the processing plant. Additional makeup water comes from wells and the Thompson River.

Improving maintenance

The size of the operation, and the age and variety of equipment all put pressures on the maintenance crew. According to maintenance manager Jim Clark, for the last decade the goal has been to maximize equipment reliability, i.e., the time of continuous running, aside from scheduled maintenance. For example, every five weeks, one of the five primary grinding mill lines is shut down for routine maintenance, which takes about 24 hours. All parts of the line including the liners and pumps, have to last for a five-week interval without additional maintenance.

The system works well. For mobile equipment, reliability comes to about 90%, and for stationary equipment it’s close to 100%. Achieving this takes a large number of mechanics — approximately 200 in the mine and another 200 in the mill — as well as adopting continuous improvements, and is also a credit to the high training standards for operators.

Reclamation and closure planning

About a third of the 6,000-ha Highland Valley property has already been reclaimed as a wilderness area, mainly the Bethlehem mine and mill site. This staged approach allows the company to experiment with methods and plant species, including input from neighbouring aboriginal bands, and allows the government regulators to become familiar with HVC’s approach, according to senior mine engineer Mark Richards.

Wildlife is abundant on the property such as a large herd of wild horses. Trojan Pond (the former Bethlehem tailings pond) has been made into a recreational fishery open one month per year, with good algal growth to feed spawning fish. Metal contents in the fish have so far been found to be safe. The Highmont tailings impoundment is currently being reclaimed as a wildlife habitat.

The ongoing monitoring includes vegetation counts. For five years, HVC has been supplementing field studies by using the infrared spectrum in satellite imagery, to remotely determine plant species and their abundance. “Generally the biomass is increasing back to the levels before the land was disturbed by mining,” says Richards, “although this is a very arid region.”

The waste rock piles are being resloped to a stable angle (about 26), followed by a 50-cm cap of overburden, and aerial seeding of grasses, plus planting with trees and shrubs. Biosolids from the Lower Mainland’s sewage treatment plants are being tested as an initial boost for growth. HVC is considering leasing some of its waste rock sites to a contractor as a brownfield site for landfill storage; the environmental assessment is underway.

Once mining is completed the pits will be allowed to fill with water and become lakes.

Human element

HVC is the largest mine in British Columbia, with more than 900 employees. It is a leader in safety, winning the province’s John Ash award for large mines in 13 of the last 16 years. Last year HVC recorded a lost-time injury rate of 0.33 per 200,000 hours worked, from the 1.8 million hours worked.

A huge investment in training began in the 1990s, particularly for the supervisory staff. “Supervisors are now better equipped to avoid problems or to detect and handle them when they arise,” says manager of human resources Rod Killough. At the same time, there is a better labour climate, with the 750 hourly employees represented by United Steelworkers Local 7619, under president Richard Boyce. Only three issues advanced last year as far as the third stage of grievance (a record low) compared with 40-50 per year a decade ago.

High standards of safety and training have resulted in improved productivity. The amount of copper plus molybdenum produced per person over a year (normalized for grade) has increased steadily from 332,000 lb in 1995 to 493,000 lb in 2005.

Extension to 2013, and beyond

When the Highland Valley Partnership began in 1986, the mine life predicted was 22 years. Closure was expected in 2009, until a $230-million extension was announced last September that will see the mine stay open until 2013.

Most of the planned extension will involve a 200-m-wide, 1-km-long pushback of the east wall of the Valley pit to expose 175 million tonnes of additional ore. The in-pit crushers and conveyors will be relocated at a cost of $30 million to the east edge of the pit next year.

The work began last year, removing the surface infrastructure from the pushback area. New equipment being purchased for $45 million this year includes 10 trucks, a loader, two dozers and a grader. The older trucks in the fleet will be thrown back into service for stripping in 2007 and 2008. The $155-million removal of 160 million tonnes of waste will be complete before the crushers arrive in their new location in the third quarter of 2007.

The transition period of 2007-09 will see the largest amount of material being moved and the highest costs, at the very time when plant throughput (and revenue) is lowest. Personnel requirements will be up to 940 this year and 980 in 2008. The plant will run at close to full capacity from 2009-12, before winding down in 2013.

HVC’s operations have a huge economic impact. Annual total spending comes to approximately $400 million. Using a 2.5 multiplier effect, this comes to $1 billion every year, and that doesn’t even include the corporate tax, which was more than $200 million last year. “It is spectacular how valuable our contribution is to the wealth of the province and the nation, from a very small footprint,” says Nickel.

The extension, therefore, has been very good news for the neighbouring communities, particularly the City of Kamloops where 400-500 HVC employees live as well as hundreds of people who work for mine supply and contracting companies. The smaller community of Logan Lake is home to 200 HVC employees, and is even more dependent on the mine.

Are there any more resources that could allow mining to stretch out beyond 2013? Certain mineralization has been designated as potential ore, depending on the markets.

The most economic mine development would be a pushback of the west wall of the Valley pit, which would garner an extra four years of production. Beyond that, a full pushback of the walls of the Lornex pit would stretch the mine life by five years. The JA deposit near the Bethlehem dump could give the mine an extra eight years of life. HVC is doing detailed engineering work and geotechnical work to assess the slope stabilities and estimate the costs.

“We won’t run out of mineralization; we’ll run out of ore,” says Frank Amon, manager of operations.

The remarkable Highmont Project

The Highland concentrator was created in 1988-89 by splicing together two plants that had been 7.5 km apart, at a cost of $70 million. The Highmont plant was moved to the Lornex site over nine weeks in the summer of 1988, along a specially built road 38 m wide and 10 km long that dropped 333 m in elevation, with grades as steep as 10%. All sections were transported intact, except for certain grinding mills. Most of the work was accomplished by Canadian contractors including heavy move contractor Premay Equipment of Edmonton. The Highmont project was a unique engineering feat in Canadian mining history.

This photo shows two tractors moving a section of the Highmont building containing a grinding mill, using multi-wheeled Scheurle trailers pinned together.

Highland Valley assembled

The parts of the Highland Valley Copper operation came together over four decades, developing its own corporate culture and a degree of independence along the
way.

Large-scale mining operations in the Highland Valley started in 1962 with the opening of the Bethlehem pit and concentrator. The Lornex pit and concentrator started up in 1972. (Lornex was owned by Rio Algom and Yukon Consolidated; the latter was bought by Teck Corp. in 1977.) In 1971, Teck bought a minority interest in Highmont Mining Co., which operated the Highmont pit from 1979 until 1984 as well as the Highmont concentrator. In 1981 Cominco Ltd. bought the Bethlehem mine and plant. It closed the mine the same year, but started up its nearby Valley pit in 1982, processing the ore through the Bethlehem plant until 1989.

The Valley pit, Bethlehem plant, and Lornex pit and plant were brought together to form the Highland Valley Copper (HVC) Partnership in 1986, still in effect today. Highmont joined the partnership in 1988, bringing all mining and processing in the valley into one operation owned by four partners: Cominco, Teck, Rio Algom (later purchased by Billiton) and Highmont. The Highmont and Lornex plant were joined to make the Highland Plant, which continues to operate.

In 2001 Teck and Cominco united as Teck Cominco Ltd. In 2004 Billiton (by then it was BHP Billiton) sold its interest in HVC to Teck Cominco, which since then has held 95% interest in the partnership. The other 5% interest is held by Highmont, owned 50% by Teck Cominco. Therefore Teck Cominco now effectively owns 97.5% interest in HVC.

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