VANCOUVER — With gold reserves up and the court-ordered closure of its Kisladag mine over for now, Eldorado Gold (ELD-T, EGO-X) looks to be back on track.
A surprise court injunction forced Eldorado to temporarily shut down its Kisladag mine, in Turkey, in late August. The injunction is part of a court case against Kisladag’s environmental impact assessment, alleged to be deficient.
On Feb. 11, Eldorado released its first news on the closure since August, reporting that the High Administrative Court in Ankara has concluded the existing expert reports prepared for the Lower Administrative Court were insufficient to make either a positive or negative decision on the case. The case will therefore now be returned to the lower court, where a new expert committee will likely be assigned to review it.
Though the case is far from over, the closure injunction expired with this decision by the high court, leaving Eldorado free to restart the mine. The company says it expects to restart the mine by the end of the quarter.
Eldorado also released its resource and reserve numbers as of Dec 31, 2007. The new numbers for Kisladag boost its proven and probable resources 14% to 153 million tonnes grading 1.12 grams gold per tonne, for 5.5 million contained ounces gold. Total resources are up 37%, to 11.1 million contained ounces gold, with most of the increase in the inferred category.
The company used a gold price of US$600 per oz. for the new reserve calculations, compared with US$450 per oz. in the previous estimate, however, Eldorado says most of the increase is due to new drilling. The 2007 infill drilling program at Kisladag uncovered new areas of gold mineralization, including a high-grade deep zone. The drilling focused on less-explored areas of the deposit, primarily to the west and south. Many drill holes ended in gold mineralization, thus the deposit is still open to the west, southwest and at depth.
Until its forced closure in August, Kisladag produced 135,300 oz. gold at a cash cost of US$198 per oz. in 2007. Eldorado anticipates 2008 will see 109,000 oz. gold produced at Kisladag, at cash costs of US$298 per oz., assuming operations resume early in the year.
Less than 100 km from Kisladag sits Efemcukuru, Eldorado’s next gold mine. The gold deposit saw a positive feasibility study in late 2007 and Eldorado is forging ahead with development. Plans call for the flotation concentrate from Efemcukuru to be transported to Kisladag for regrinding and cyanidation. The company also continued drilling at the site and in doing so increased Efemcukuru’s resource count slightly, compared to the recent feasibility study estimate, by adding a new section of the North oreshoot.
Efemcukuru now hosts measured and indicated resources totalling 4.09 million tonnes grading 11.01 grams gold, plus inferred resources of891,000 tonnes grading 8.32 grams gold. Incorporating a pit design, the project offers proven and probable reserves of 3.79 million tonnes grading 10.04 grams gold, for 1.22 million ounces contained gold.
technology. Using ideas first put forward by Frank Forward of the University of British Columbia, the research group, called Sherritt Technologies, designed and built a plant in Fort Saskatchewan, Alta., to extract nickel and cobalt from concentrate from its mine in Lynn Lake, Man., using a process that deviated markedly from pyrometallurgy (smelting) — the then-current technology that continues to dominate the base metal extraction industry in Canada today.
Hydrometallurgy has one big environmental advantage over smelting: the former emits no sulphur dioxide, the main cause of acid rain. Rather, the sulphur is captured and used to make elemental sulphur or combined with ammonia to make fertilizer.
Sherritt Technologies went on to develop pressure hydrometallurgical processes for other metals including gold, zinc, copper and uranium; so far it has licensed more than 35 commercial partners to use Sherritt technology.
The group continues to be in the forefront of pressure hydrometallurgical
technology, offering clients concept development and testing in their lab in Fort Saskatchewan, scaling up the design to commercial size, as well as helping with construction, commissioning and ongoing operations.
From its half-century bank of experience as well as never-ending tweaking of the Fort Saskatchewan nickel hydrometallurgical plant, the Technologies group can now forego the expensive and lengthy progression of bench test, mining pilot plant, pilot plant and demonstration plant. Nowtheygo directly from the small-scale pilot plant tests with 1-to 2- tonne samples, and scale up to the commercial plant.
“One of our great strengths is that we are not only technologists, we are also operators. We are actually selling our know-how,” says Robin Kalanchey, business development manager for Sherritt Technologies.
Fort Saskatchewan
The Sherritt Pressure Hydrometallurgical Plant, also known as Corefco (“The Cobalt Refinery Co. Inc.”), began operations in 1954. It was located in Fort Saskatchewan for three reasons: a ready supply of natural gas (the main energy source); access to water; and the town’s location on the Canadian National Railroad line, just north of Edmonton.
When Lynn Lake feed began to dwindle in the early 1970s, the plant started taking on additional feeds. It received its first mixed sulphide feed from the Pedro Sotto Alba plant in Moa, Cuba, in 1991; Moa today supplies about 95% of the plant’s nickel feed.
While the configuration of the leach stages and autoclaves has been altered many times over the last half century, the basic function and operation of the ammonia leach process has remained remarkably constant.
A tour of Corefco in early February revealed a 50-year-old chemical plant, with a zillion pipes and valves leading to and from autoclaves, tanks and towers, showing the effects of generations of alterations and improvements.
In the three-stage leaching process, the nickel-cobalt suphide is fed into autoclaves, where it is mixed with ammonia and air, dissolving the nickel and cobalt. The remaining solids (mainly iron oxide) are filtered out, washed and stockpiled or sold.
Selective crystallization separates cobalt from nickel. The resulting cobalt salt is redissolved in the cobalt plant. In a continuous batch operation, hydrogen is injected into the reduction autoclaves causing cobalt to precipitate onto cobalt seed powder, which is kept in suspension by agitators. The depleted solution is drawn off and fresh solution is added until the cobalt particles reach the required size. The slurry is discharged to a flash tank, and the cobalt powder is filtered out and washed. The 99.8% pure cobalt powder is dried and packaged, or is compacted into briquettes and sintered to form a 99.9% cobalt product.
Meanwhile, the nickel-rich solution remaining after cobalt separation
flows back to the leach plant where leached copper is removed by lowering the pH until the copper combines with sulphur. The solid copper sulphide is separated by a thickener and polish filters. This is sold as feed to a copper smelter.
An oxyhydrolysis tower treats the clarified nickel-rich solution at high temperature to eliminate unsaturated suphur compounds and sulphamate.
Then the solution enters the nickel plant, where reduction autoclaves function in a similar way to the cobalt reduction autoclaves, in a continuous batch process. Hydrogen gas is added, the autoclave is agitated and nickel comes out of solution, depositing onto nickel seed powder. The depleted solution is drawn off, replaced by fresh solution and this continues until the nickel particles reach the required size.
The slurry is discharged into the flash tank and transferred to a pan filter where the nickel particles are washed. The powder is dried and packaged (99.8% pure nickel), or compacted into 99.4% nickel briquettes that may be sintered to 99.8%. The briquettes f
orm 90% of the product, and are shipped in 2- tonne bags to customers in Europe and Asia. (With the metals originating in Cuba, these products may not be sold into the United States.)
Minor nickel and cobalt remaining in the depleted solution are precipitated as sulphides using H2S, and removed by a filter press. The filtered solution now contains mainly ammonium sulphate, which is recovered by evaporation in the ammonium suphate plant, and converted into fertilizer, which is sold in Western Canada.
Pressure hydrometallurgy eliminates the emission of SO2 (most of the white “smoke” coming out of the plant’s stacks is actually water vapour).
Corefco has eliminated the impounding of new slurry (containing iron oxide solids from the leaching plant) through process innovations and filtering, as well as water-borne emissions that are processed at a regional treatment facility. Air emissions have remained below regulated limits.
There has never been a strike in the plant’s 54-year history. The current labour agreement will continue to 2010.
Corefco’s output has increased dramatically over the years. The eight autoclaves in the plant were originally designed to produce 7,700 tonnes per year of combined nickel plus cobalt, but the same eight autoclaves today can make about 32,000 tonnes per year of nickel and 3,500 tonnes per year of cobalt.
Plans are in place for another large expansion to accommodate the increases in feed that will be coming from the Moa plant beginning in mid-2008.
Moa Bay
Feed for the Corefco plant comes mainly from the Moa mine and concentrator here in eastern Cuba. The operation was built by Moa Bay Mining Co., a subsidiary of Freeport Sulphur, using propriety Sherritt technology.
The 25,000-tonne nameplate capacity plant began operation in 1959, the year of the Cuban Revolution. The Cuban government took over the operation and restarted it in 1961. With the collapse of the Soviet Union 30 years later, the Moa facility needed a new home for its feed, so it began to send its mixed sulphides to Sherritt’s Fort Saskatchewan facility in 1991.
Sherritt saw Moa as more than a steady source of feed for Corefco. It saw an opportunity to improve the performance at Moa, so Sherritt formed a 50/50 joint venture with Cuba’s General Nickel Co. (part of the country’s Ministry of Basic Industry) in 1994. The operating joint-venture company, Metals Enterprise, consists of the Moa mine and processing facilities (Moa Nickel S.A.), the Corefco plant, and its marketing arm, International Cobalt Co.
Today, all of Moa’s mixed sulphide is shipped to Fort Saskatchewan.
Moa operations have prospered under the joint venture. Production of contained nickel and cobalt was only 12,500 tonnes in 1994, but, as a result of debottlenecking, has almost tripled and should be about 33,000 tonnes in 2007, according to guidance provided by the company last fall.
The cost of production dropped steadily by 2003, but has risen recently due to jumps in the price of acid, sulphur and oil. The operation’s employees at Moa include about a dozen expatriate Canadians.
After 54 yearsofoperation, Moa’s West mine is nearly depleted, with 75% of the limonite now coming from the East mine. Overburden is stripped to uncover the soft limonite (ore) layer. The underlying saprolite is being left exposed, available for future recovery for ferronickel operations at the request of the government, preventing reforestation of some land at this time. However, Moa Nickel has in place a full-fledged program that will ultimately address all reforestation requirements.
Nine excavators feed 10,000 tonnes of limonite per day into trucks which haul it up 6 km to the slurry plant. Expansion plans call for the development of a new slurry facility, which will reduce haulage distances for the mobile fleet. A 300,000-tonne stockpile is built up each year before the rainy season.
Limonite is slurried with water and screened to remove the coarse magnesium-bearing serpentine ore (about 15%), and then pumped 5 km to the plant. Thickeners there increase solids content to 47%, and return water to the slurry plant. The limonite slurry reports to the acidleach plant.
Five sulphuric acid-leach trains, each consisting of four pachucas, leach 95% of the nickel and cobalt from the slurry with a retention time of about 75 minutes. Seven countercurrent-decantation (CCD) tanks separate the solids from the metal-rich solution; the tails are treated and pumped to the tailings pond. Hydrogen sulphide is then added to remove copper and reduce chrome and iron; and the addition of limestone excavated from nearby Moa Bay increases the pH to 2.5.
Hydrogen sulphide is injected into the purified liquor in autoclaves to precipitate nickel and cobalt as mixed sulphides, which are thickened and dried to a concentrate containing about 55% nickel, 5.5% cobalt, 1% iron, 1% zinc and 0.03% copper. This is shipped from Moa Bay to Halifax, N.S., and railed to Fort Saskatchewan.
Substantial surge capacity allows for critical maintenance on the acidleach reactors and sulphide precipitation autoclaves while the rest of the plant continues to operate.
An expansion project launched in 2005 will take Moa’s production from 33,000 tonnes per year to at least 46,000 tonnes of combined nickel and cobalt.
Consulting firm Hatch Associates is handling the construction management, with about 600 additional construction employees, mainly Cuban, currently involved. The Cuban partner will provide sufficient laterite concessions for an additional 25 years of operation.
The expansion’s first phase began in 2005 and will be commissioned in the first half of this year, increasing the capacity to 37,000 tonnes per year. The mining rate will increase, mainly from the East mine. An additional thickener will dewater the slurry. The CCD circuit is being extended by three tanks, and neutralization capacity is doubling. There will be another large autoclave for sulphide precipitation.
The second expansion phase will boost annual output to 46,000 tonnes and will include another leach reactor train. An additional sulphuric acid plant will make the processing facility virtually self-sufficient for acid supply. –The author is editor of the Canadian Mining Journal. For Werniuk’s full report on all of Sherritt International’s business units, including an interview with president and CEO Jowdat Waheed, see the February 2008 edition of the Canadian Mining Journal. www.canadianminingjournal.com
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