Marilyn Scales is a field editor for the Canadian Mining Journal, Canada’s first mining publication. She is one of Canada’s most senior mining commentators.
Site Visit By Field Editor Marilyn Scales
A true partnership has been forged by Agnico-Eagle Mines and the Inuit of Baker Lake, Nunavut, one that treats the land with respect and provides a modern future for young members of the community. The elders have embraced Agnico’s vision of gold mining. They know mining will provide education, training and well-paying jobs for many years. And most importantly, they trust Agnico to be a responsible steward of their land.
The Meadowbank project offered many firsts for all involved. It is the first project Agnico has pursued in the Arctic. It is the first gold mine in Nunavut (and currently the only mine). It is the first to be developed on Inuit land. It is the first mine to be covered by a water compensation agreement, signed in April 2008 with the Kivalliq Inuit Association.
Agnico gained control of the Meadowbank deposit when it purchased Cumberland Resources in 2007. Cumberland had great success exploring the deposit in the previous decade. A pre-feasibility report was completed in 2000 and updated five years later. The takeover of Cumberland cost $710 million, but it increased Agnico’s gold reserves by 23%.
The acquisition brought with it 10 Crown mining leases and three Nunavut Tunngavik exploration licences in the Kivalliq District, 70 km west of Baker Lake. Three deposits -Portage, Goose Island and Vault -dot the property along a 25-km-long trend. The gold deposits are of Archean age and hosted within volcanic and sedimentary rocks.
The economic mineralization of the Portage and Goose deposits occurs as pyrrhotite, which is a replacement for magnetite in the banded iron formation host rock. Pyrite and chalcopyrite are also found, and on rare occasions arsenopyrite associated with other sulphides. Sulphide occurrences are variable in content and range from trace to semi-massive. The sulphides occur as narrow stringers that almost always crosscut the main foliation. Higher gold grades are generally associated with sulphide content greater than 20%.
The deposits lie within 225 metres of the surface, making open pit mining possible. They are known to be only a few metres wide in the lateral direction, but also appear to be open at depth.
At the end of 2009, exploration had outlined 600,000 tonnes of proven reserves grading 4.57 g/t Au and 31.60 million tonnes of probable reserves grading 3.51 g/t. The reserves contain a total of 3.66 million oz of gold.
Indicated and inferred resources are divided into portions recoverable by open pit or by underground methods. Resources that can be mined by open pit are 40.98 million tonnes at 2.34 g/t Au (indicated) and 9.17 million tonnes at 2.54 g/t (inferred). Material that is amenable to underground methods is 1.39 million tonnes at 5.23 g/t (indicated) and 16,000 tonnes at 6.12 g/t (inferred). Indicated and inferred resources contain as much as 4.06 million oz of gold. The potential at Meadowbank is great.
Having spent $710 million to acquire Cumberland Resources and the Meadowbank project, Agnico made plans to spend roughly the same amount developing an open pit mine and processing plant capable of producing an average of 400,000 oz of gold in each of the project’s first four years and 350,000 oz/yr thereafter. The first doré bar was poured in Feb. 27, 2010, and commercial production was marked by the official opening ceremony on June 18.
Agnico has built a barge landing site and fuel storage and distribution complex about 3.0 km east of Baker Lake. Annual supplies are barged to the site during the short summer season. A 110-km all-weather road connects Baker Lake with the mine site, so that material can be moved by truck to the mine as needed.
Facilities at the mine site include a per- manent camp for 364 people and an 80-person exploration camp a few kilo-metres to the south. The camp has sewage treatment, solids waste disposal and potable water plants.
Other facilities include the mill building, an assay lab, a mechanical maintenance shop, a heavy vehicle maintenance shop, and a domed structure to house the ore stockpile. Power is supplied by Caterpillar 4.4 MW diesel-electric generators with heat recovery. Up to 5.0 million litres of fuel can be stored at the site.
Mining and milling
The Portage pit is the first mining target. The area was originally covered by much of Portage Lake, that meant dykes had to be built to make the deposit accessible. Agnico spent 18 months building the East dyke to contain the 16 million litres of water pumped out of what became the pit. It is an expensive undertaking, especially when considering there are a total of six dykes to be built during the project.
Mining proceeds with conventional blasting, loading and trucking. Ore is delineated by a low-tech series of flags and ribbons until a GPS system is installed. Atlas Copco drills punch 150-cm blast-holes that are loaded with emulsion. Using Anfo in the wet and freezing conditions proved problematic last winter, and a Dyno emulsion plant has been built at the mine. Blasting occurs two or three times each week to break approximately 100,000 tonnes at a time, depending on the outlined blocks and anticipated vibration. Run-of-mine ore is loaded into Cat trucks by O&K hydraulic excavators and trucked to the Metso gyratory crusher adjacent to the mill. The crusher is set at 150 mm. Crushed ore is stored in a distinctive dome-shaped structure.
From start up through 2013 all of the ore will come from the Portage pit. Waste material will be used to build the remaining dykes or stored in a primary dump. When the Bay-Goose dyke is completed in 2013, mining will begin in the Goose Island pit. Mining of both the Portage and Goose pits will take place from 2013 to 2014. Beginning in 2015, and for the last four years of the mine life, ore will come exclusively from the Vault pit, where drill core has assayed as high as 405.5 g/t Au.
Crushed ore is conveyed from the storage dome to the grinding circuit in the mill building. Ore is ground in a Metso SAG mill with a pebble crusher. A Metso ball mill operating in closed circuit with cyclones regrinds the particles as necessary. The target grind is 80% passing 60 to 90 microns.
The mill has a throughput of 8,500 t/d, and already a scoping study is underway to examine the possibility of increasing the rate to 10,000 t/d. Gold is recovered by gravity and carbon-in-pulp (CIP) technology. Free gold, roughly 25% to 30% of the gold in the ore, is removed by a Falcon concentrator. The slurry then passes into the cyanidation unit and on to the CIP circuit that consists of seven agitated tanks. Carbon is removed from the last tank, and the gold is stripped using an acid wash at 135°C and 380 kPa over a period of 15 hours. The pregnant solution, containing between 5,000 and 10,000 g/t Au, is then passed through electrowinning cells. When the gold has precipitated onto the cathodes, they are smelting and doré bars poured.
The environmental aspects of the Meadowbank mill were carefully designed. The plant includes both a cyanide recycling thickener and an air-sulphur dioxide cyanide destruction circuit. All water in the tailings pond is recycled, making this a zero-discharge system and reducing the need for fresh water.
Due to its sulphide content, waste rock has the potential to be acid generating. To minimize oxidation it will be encapsulated in permafrost and capped with an insulating layer of neutralizing rock. Because the site is underlain by about 450 metres of permafrost, the waste rock is expected to freeze beneath the cap, greatly reducing acid drainage in the long term.
As mentioned above, Meadowbank is the first project to be covered by a water compensation agreement between the company and the Inuit. It addresses Inuit rights under the Land Claims Agreement respecting compensation for water use and water impacts that may occur.
Agnico’s goal is to minimize the potential impact of the operation on surface water and groundwater at the site. In addition to a zero-discharge tailings management strategy, the company has agreed to build diversion ditches to avoid the contact between clean runoff and water from areas affected by its mining and processing activities. Water from the disturbed site area will be collected and stored in the tailings pond.
Agnico-Eagle enjoys the trust and support of the Inuit because it has been able to bring some of the community’s dreams to reality. Before the Meadowbank mine project began, unemployment in Baker Lake was 40%; now it is only 4.5%. The mine employs 180 Inuit workers.
A golden future
The prospects for the future are excellent. Continued exploration at Meadowbank is expected to discover even more hidden ounces in the future giving the project an even longer life. Agnico has completed the takeover of Comaplex Minerals, owner of the advanced Meliadine gold project consisting of a East and West deposits.
The Meliadine project is 300 km from the Meadowbank mine. Agnico is looking at a 7,000 t/d mine and mill. There are an estimated 3.3 million oz of gold in a measured and indicated resources of 12.9 million tonnes grading 7.9 g/t Au plus an inferred resource of 8.4 million tonnes grading 6.4 g/t Au for 1.7 million oz.
Development and mining the Meliadine gold project will keep Agnico busy in the far north for many years to come. That is exactly what the company plans to do.
Said chief operating officer Ebe Sherckus, “The Arctic does get under your skin. I love it. It’s a place we hope to be for a long time. Meadowbank is our stepping stone to other things.”