Cominco’s Alaskan Triumph

The US$414-million (capital) Red Dog mine opened in 1989 with the likelihood of having the world’s best zinc deposit. There were nagging questions, however, particularly surrounding the zinc market, the metallurgy and working in this remote corner of Alaska. Those doubts were justified; six years would pass before the operation began to make money.

Through an almost continuous series of expansions and improvements, the 11-year-old mine is now the world’s largest producer of zinc concentrate, with costs in the lowest quartile. Its latest expansion, known as the VIP (Value Improvement Program) Mill Optimization Project, will be completed by October 2001. The mine was preparing to receive two massive modules for the project when CMJ visited the site in September 2000.

Red Dog is a significant contributor to the current success of its operator, Vancouver-based zinc-lead giant Cominco Ltd. In 2000, Red Dog’s revenue of Cdn$433 million formed 23% of the company’s total earnings, while its Cdn$127-million operating profit was 32% of the company’s as a whole.

Last year, the Alaskan operation produced 960,000 tonnes of zinc concentrate containing 55.3% Zn plus 3.4% silica, and 140,000 tonnes of lead concentrate containing 59.6% Pb, 10.3% Zn and 380 g/t silver. This was 74% of all the zinc concentrate and 62% of all the lead concentrate that Cominco properties made in 2000. (The rest came from the Sullivan mine in British Columbia and the Polaris mine in the Northwest Territories, both of which are slated to close in 2002.) Last year, Red Dog provided 60% of the zinc concentrate for Cominco’s Trail smelter in B.C. (see CMJ December 2000).

The mine is operated by Cominco’s wholly-owned subsidiary, Cominco Alaska Inc. under a long-term lease agreement with NANA Regional Corp., Inc. (NANA), an Alaskan Native corporation.

The land on which the mine and plant lie is owned by NANA, which signed a progressive and visionary agreement with Cominco in 1982. The Red Dog Operating Agreement is the basis of the development and operation of the mine. It includes commitments to protect the environment, provide training and employment for NANA residents (“shareholders”), and an increasing sharing of the profits with NANA over the life of the mine, which promises to be at least 40 more years.

The mine’s location in northwest Alaska is not easily accessible. It is 1,000 km north of Anchorage and 140 km north of the Arctic Circle. The mine is 84 km inland from shallow tidewater on the Chukchi Sea, which is only open to shipping 100 days per year.

Why go to the trouble of mining metals worth less than US$1 per pound in such a formidable location? The orebody is just too rich and large to pass up. As operations manager Tim Smith says, “It’s a good thing it’s a 20% zinc ore deposit; otherwise it wouldn’t fly.”

For background on Red Dog, see CMJ June 1989 (pp. 63-67) and CMJ Trail Supplement, September 1996, pp. 24-30.

Exploration and Mining

Red Dog has the world’s largest zinc reserve. Four deposits are grouped together near the concentrator; the Main, Aqqaluk and Qanaiyaq are at surface, and the Paalaaq lies at a depth of 180 to 425 m. As well, there are two other zones of mineralization in the region–the Su-Lik deposit 19 km to the northwest and the Arjarraaq deposit 10 km north; the latter was discovered in 1999. Most of Arjarraaq lies more than 600 m below surface. To date, mining is confined to the Main zone; many exploration targets are waiting to be examined.

Red Dog’s sulphide ore zones lie in sedimentary exhalative (sedex) deposits within Mississippian to Permian black shales. They are overlain by barite-rich rock and a 20-30-m-thick cap of oxidized mineralization. Most of the weathered (oxidized) material has already been mined from the Main deposit. The fragmented nature of the rocks and high-grade zinc-lead veining is unusual in sedex deposits. Water-soluble zinc and iron sulphates, and abundant bitumen and native sulphur all make for challenges in the plant.

The table below outlines the reserves and resources of the four nearby deposits as of the end of 2000. As well, the Su-Lik deposit, covered by U.S. Federal mining claims, is owned by Cominco and GCO of Houston, Tex., and is estimated to contain 34 million tonnes grading 8% Zn, 2% Pb and 30 g/tonne Ag. Arjarraaq contains an inferred resource of 17.2 million tonnes grading 15.8% Zn, 4.8% Pb and 71 g/tonne Ag.

The Aqqaluk deposit was drilled off last summer on closely-spaced centres in order to define the reserves, but will not be mined until the Main zone is completed in 2012. Metallurgical samples were obtained from Qanaiyaq this past winter in order to determine if it would be more efficient to mine it first.

Because of the high grade of the Main deposit, the open pit mining operation is relatively small. Currently, the mine operates two 16.5-cm-diam Ingersoll-Rand rotary blasthole drills. The production Caterpillar equipment includes two 992 front-end loaders, five 777 haulage trucks and two D9R dozers. Mine production is 18,000 tonnes of ore and waste per day. Run-of-mine ore is blended in stockpiles. These stockpiles are then fed to the gyratory crusher at 9,000 tonnes per day. To further facilitate grade control, four benches in the pit are used for ore extraction.

Mine geologist Tom Krolak explains that the low stripping ratio (1:1) is a big cost saver, but the complex structure and mineralogy adds costs. “There are a variety of ore types and grades. The cutoff grade is 6-7% Zn, and once in awhile the grade goes up to 40-45% Zn. There can be high barite or iron content. Also there is sulphide veining in silicified black shale. All of it is fair game. We have to keep the TOC [total organic carbon] content below 0.6% in a stockpile or it causes adverse effects in the lead concentrate.”

Each quarterly mine plan is divided into shots of 36,000-54,000 tonnes each; there are blasts about three times a week. Drill cuttings from every blast are assayed to provide an accurate assessment of grade. Ore stockpiles are built in five lifts and are carefully planned to be reclaimed. “We have to do a balancing act to deliver a steady 20-21% Zn to the mill every day. We give it lots of attention; the additional costs are justified by improved mill performance.”

Ore Processing

The technical challenges at Red Dog are mainly metallurgical. Along with one of the world’s highest zinc feed grades comes the highly variable mineralogy typical of a sedex deposit.

The plant includes conventional crushing, grinding, flotation and dewatering. There are three stages of grinding followed by a prefloat to eliminate some of the organics. Lead flotation is followed by zinc flotation. Each circuit involves roughers and regrind followed by cleaning. The ore requires a relatively fine regrind in tower mills to ensure an adequate liberation of both lead and zinc. The zinc and lead concentrates are dewatered to 9% moisture using thickeners followed by pressure filters, and are then hauled by truck to the port for summer shipment.

The complex orebody requires a large technical team. One of the plant metallurgists, Chad Parent, comments: “We have a good handle on the ore, but at times we have to think outside the box.”

A series of expansions have relieved certain bottlenecks but introduced others. The US$200-million Production Rate Increase, completed in 1998, increased the crushing and grinding throughput by 40%, but did not provide sufficient additional flotation capacity.

Mill Optimization Project

A planning session in July 1999, led to a long-term strategy, named Red Dog VIP (Value Improvement Program). It was clear that certain items had to be taken care of right away to reduce risks and ensure the existing production. These included the addition of another generator (to have one on hot standby), the addition of a new zinc thickener and expansion of the water treatment capacity to handle the water balance situation.

A flotation circuit expansion would increase the revenues by inc
reasing both the quality and quantity of the concentrate. The result would be to increase the annual throughput to 3.5 million tonnes. Zinc recovery would increase from 83% to 87%, to produce 1.06 million tonnes of zinc concentrate containing 56% Zn and 2.8% silica. An additional generator would be needed to power the expanded flotation.

This US$105-million set of improvements–called the VIP Mill Optimization Project–was proposed in December 1999, and given preliminary approval in January 2000 (see sidebar below). The major elements include:

the addition of two 5-MW diesel generators in a new powerhouse building. This will supplement the existing six 5-MW generators and provide a fully redundant standby spare.

the construction of an 8.7-million-L fuel tank at the port. The annual fuel consumption will rise to almost 72 million L.

installation of a new 43-m-diam zinc concentrate thickener. The existing 18-m-diam zinc thickener is being converted to lead thickening. The existing 10-m-diam lead thickener is going to become a wash water collection and surge tank.

upgrading of water treatment plant No.1 to process up to 26,500 L/min and upgrading of the No.2 plant to process 60,500 L/min.

the addition of 21 new 50-m3 Outokumpu mechanical flotation cells and four new 3.6-m-diam flotation column cells. The 12 zinc rougher cells and four column cells (for cleaning) are housed in a module. There is also an on-site expansion of the existing lead flotation building, and several parts of the existing plant will be revised and upgraded to suit the new circuit.

Environmental Controls

Red Dog’s location in an area dependent on subsistence hunting and fishing means that environmental controls are critical to the lifestyle of the local population. Perhaps the most keen of the mine’s environmental watchdogs is the Subsistence Committee, composed of Inupiat elders from two of the closest villages.

The eight to ten people in the environmental department oversee the waste-water treatment, sewage treatment and drinking water systems. Potable water for the Permanent Accommodation Complex (PAC) and camp is drawn from Bons Creek reservoir.

The mine’s environmental department spent US$2.6 million last year on various monitoring programs. These include monitoring the water and air quality, ambient dust from operations, and the integrity of the tailings dam, waste rock stockpiles and the open pit. The department also conducts or manages programs to monitor algae, macro-invertebrates and fish in waters up to a 32-km radius from the mine and port sites and along the road. It also runs three meteorological stations.

In a land frozen from mid-October until mid-April, with abundant precipitation in all seasons, managing the water balance is a major job. Contaminated water from all sources is collected in the tailings impoundment, which can hold two years of collected water. Water in the impoundment contains dissolved metals in sulphate form, including 250 mg/L Zn, 3.5 mg/L Pb, and 4 mg/L Cd. Metals control is the most important environmental water issue; however, total dissolved solids (TDS) is currently the greatest permitting obstacle. A water discharge strategy has been developed to ensure the TDS is kept below the permitted level of 1,500 mg/L in the receiving waters.

“Nobody out there matches us in the treatment and reduction of metals in water,” says Wayne Hall, one of Red Dog’s three environmental co-ordinators. Red Dog uses a high density sludge process designed by Cominco Engineering Services Ltd. There are two water treatment plants at Red Dog: a year-round plant (No.1) to treat 21,000 L/min of water before it is recycled to the mill, and a summer plant (No.2) to treat water before discharge to the environment. The summer plant only operates from mid-March until mid-October, when the surface water is flowing; this releases treated water to Red Dog Creek at a rate up to 42,000 L/min. Metallurgical engineer Jason Weakley describes how the two plants work.

The process uses lime to precipitate zinc, lead and iron as hydroxides, and sodium sulphide to precipitate cadmium. The majority of the precipitated solids are removed by settling in a 61-m-diam clarifier but the solution is also polished with two 6.9-m-diam sand filters to remove any suspended solids. After treatment the water contains 70 mg/L Zn, 1-2 mg/L Pb and <1 mg/L Cd and measures 0.7 net turbidity unit. This is well within the allowable limits for discharge.

Selenium is one of the most recent parameters added to the permitting regime at Red Dog. Initially selenium levels were measured at elevated levels; however, in recent years the selenium levels have remained below permitted limits. Cominco continues to research the dynamics of selenium in the water balance through co-operative agreements with the University of Idaho.

The mining operation is allowed to release 9.1 billion L of water per year. “The only kicker is that we have to meet the in-stream TDS permit limit,” says Weakley. “As the summer becomes drier and stream flows drop, we have to cut back on our discharges to keep below the TDS limit.” The Mill Optimization Project will increase the treatment capacity. Hall explains: “We want to increase the plant to 15,000 gallons [57,000 L] per minute to take advantage of days with high stream flow for maximum discharge.”

Red Dog Creek was naturally contaminated with metals before mining activities began, because it flowed through outcropping mineralization. To prevent this from continuing, the creek was redirected through a lined ditch. The combined effects of the lined ditch and the discharge of treated waters (that are lower in metals concentrations than the naturally occurring baseline waters) has resulted in significant water quality improvements.

Transportation Challenges

Red Dog’s remote location makes transportation one of its main costs. Personnel, perishables and freight arrive by air from Anchorage and the surrounding villages. The airport at the mine is capable of receiving airplanes as large as 727s. Fuel, equipment, and annual operating supplies arrive by barge at the state-owned, Cominco-operated DeLong Mountain Port Facility, and are then transported 84 km by gravel road to the mine.

Since the cost to transport goods by air from Anchorage to Red Dog is 10 times the cost of barge freight, the preferred choice is obvious. However, the port is only accessible for about 100 ice-free days per year. During those 100 days, the Port Operation handles 32,000 tonnes of freight, nearly 75 million L of diesel fuel, and over one million tonnes of concentrates.

NANA/Lynden hauls the concentrate from the mine to the port site, as well as 68 million L of fuel and 136,000 kg of freight in the opposite direction. The same company also handles the barging of freight from Seattle. The company’s 59 employees at the site keep the haulage going around the clock throughout the year. NANA/Lynden operations manager Mark Tatlow describes the operation.

“The dewatered concentrate is hauled in 15 covered concentrate trailers; in the Port unloading facility, the complete tractor and trailer unit is tilted and vibrated to empty the concentrate out. Nine new custom-built units are scheduled to arrive this summer. They will be self-dumping and self-cleaning, eliminating winter problems with material freezing in the trailers.”

The zinc and lead concentrates are stored in two separate buildings at the port. They can store almost a million tonnes of concentrate, about nine months of production. As with farmers, the crunch comes in the fall when the concentrate storage buildings are empty and the last two ships of the season are filled directly from production.

The fuel is moved in a 95,000-L tanker, and there are six trailers for freight. Storage tanks at the port and mine can hold enough diesel fuel to support nine months of operation.

Although the road was constructed using the best arctic engineering designs and has proven its durability over the last 12 years, continual maintenance is required to control mud and dust to keep the road in top
condition. Cominco and NANA/Lynden are investigating a new seal coat material called High Float that is being successfully used as a road surface in arctic conditions. High Float surface coating has the potential to effectively eliminate mud and dust on the road.

A permit limits the number of truck trips to the port based on the amount of dust generated by the trucks. The weight and type of truck and trailer, and characteristics of the road surface determine the amount of dust generated by a truck trip.

The drivers target three round trips to the port per 12-hour shift, although some drivers can make four. Training is continuous; it takes two to three years to develop the solid skill levels to become a top driver.

The water is so shallow at the port and the slope so gentle that the ships have to anchor five kilometres offshore, and concentrate is transported to them by two lightering barges and four tugboats operated by Foss Maritime. The lightering barges carry 5,443 tonnes of concentrate per load; they can only operate in relatively calm seas.

Twenty-one ships carried concentrate from Red Dog last year of which five were bound for Vancouver harbour (for Cominco’s smelter in Trail, B.C.) while the balance went to ports in Europe, South Korea, Japan and Australia. Six barge loads of freight and five barge loads of fuel arrived at the port in 2000 as well as one barge bearing the two modules for the Mill Optimization Project.

Reserves and resources in the four deposits at the Red Dog mine site

	Tonnes	Zn%	Pb%	Ag	(000)	g/tonne
Proven reserves (Main)	41,900	19.2	5.2	100
Probable reserves (Aqqaluk)	56,100	16.6	4.1	76
TOTAL RESERVES	98,000	17.7	4.6	86
Indicated resources (Qanaiyaq)	9,600	17.8	5.5	117
Indicated resources (Aqqaluk)	3,400	9.8	3.7	78
Inferred resources (Aqqaluk)	6,800	6.5	3.6	59
Inferred resources (Paalaaq)	13,000	15.0	4.0	90
TOTAL RESOURCES	32,800	13.5	4.3	90

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