It may be premature to begin development of Ontario’s second diamond mine, but De Beers Canada is giving the most likely candidate – the Tango Extension kimberlite – a thorough going-over.
The Victor diamond mine became Ontario’s first when it opened in 2008, but its life was known to be limited to about 12 years. Now halfway through the resources, De Beers is looking at some of the 18 other kimberlites nearby. The Tango Extension kimberlite (not to be confused with the Tango kimberlite) is at the advanced exploration stage, but appears to be the most likely to extend the life of the Victor processing facilities.
Before looking at what is officially the “Victor mine extension project,” a brief review of the mine and facilities is in order.
The wilds of Northern Ontario is never going to be a cheap place to build a mine, and De Beers spent slightly more than $1 billion developing the Victor pit, the processing facilities and the permanent camp in the swampy muskeg of the James Bay lowlands.
The processing plant has an annual capacity to treat 2.7 million tonnes of kimberlite, recovering a nominal 600,000 ct of diamonds each year. In 2011 the output was significantly higher, 779,000 ct.
Because the diamonds are of exceptional value (US$400 per ct in the rough state), the recovery plant is highly automated. Missing even one stone would have a negative impact on profits. The plant relies on dense medium separation and x-ray sorting. Processed kimberlite is not acid generating and stored on site.
More detail is available in the January 2009 issue of CMJ.
The nearest aboriginal community is Attawapiskat 90 km away. De Beers established a marshalling yard there to assemble material that must be trucked to the mine site over a winter road, otherwise access is via air for small supplies and the workforce of roughly 500, more than 40% of whom are aboriginal. De Beers has signed impact benefit agreements with the Attawapiskat, Moose Cree, Kashechewan and Fort Albany First Nations. A working relationship is also in place with the Taykwa Tagamou Nation.
The closure of the Victor mine is anticipated in 2018. Progressive reclamation has already started. That will be followed by post-closure reclamation into 2021 and environmental monitoring thereafter.
Rather than let an expensive processing plant and state-of-the-art accommodation complex go begging, De Beers has been exploring the other kimberlites near Victor. The most promising so far is the Tango Extension less than 8 km northwest of the Victor mine.
The geology of the Tango Extension kimberlite is similar to that of the Victor kimberlite. It has the classic champagne glass shape, formed by continuous volcanic activity 160 million to 170 million years ago. The kimberlite is subdivided into four geological units, each with a different grade and diamond size characteristics. The surface of the Tango Extension measured approximately 7.7 ha, and drilling has revealed that it extends to 292 metres below surface, although not all of the deepest portion is mineable.
The host rock is comprised of limestone with sections of mudstone. The kimberlite is overlain by about 20 metres of marine clay topped with a few metres of peaty muskeg typical of the area. The finished pit area will cover 36 ha as reflects the removal of the overburden. Stockpiles of mine waste rock, overburden and peat, plus the roads associated with mining, will occupy approximately 330 ha.
Key to the viability of developing the Tango Extension is that the processing plant, mining fleet, workforce and infrastructure are already on site. Mining at a nominal rate of 3 million tonnes annually will keep the Victor diamond recovery plant at capacity. The fleet – including Caterpillar 385 and 992 loaders, one Tramac/Montabert EXC2 blasthole drill, plus two Cat 777, four Haul Max and two Cat 733 trucks – will be moved to the new pit. Employees are skilled and their accommodations in place. The processed kimberlite containment area is permitted and can accept tails generated by a further five years of mining. The site has a source of power and transportation links.
De Beers has already been in general discussions concerning Tango Extension with the First Nations who are party to impact benefit agreements. The IBAs contain clauses that include work to extend the mine life within the original agreements.
Water management is expected to be very similar to the Victor mine. A series of dewatering wells will discharge clean Surface water will be treated on site and either discharged with the dewatering well water, or discharged to the muskeg wetlands. Wastewater from site washroom facilities will be trucked to the existing Victor facility for treatment.
During the permitting phase, De Beers and the Ministry of the Environment will determine, based on detailed hydrogeological modeling, to what extent any seasonal flow supplementation of nearby muskeg streams might be necessary. This precautionary practice has been proven to be effective during the operation of the Victor mine.
Wastes will continue to be managed as at Victor. Stockpiles of muskeg peat, overburden, waste limestone-mudstone and possibly low grade kimberlite will be established close to the Tango Extension mine. These will eventually be reclaimed and re-vegetated using methods previously proven at Victor.
Processed kimberlite ore, after recovery of the diamonds, will initially continue to be placed in constructed above-ground containment dikes as is the case at Victor. However, the environmental assessment will evaluate the option of placing both coarse and fine processed kimberlite wastes into the former Victor mine pit. This latter option is expected to substantially reduce the environmental footprint of the mine and also improve the economics of the project.
The extensive environmental monitoring and research programs for the Victor mine provide confidence that the Tango Extension project can go ahead with minimal environmental impacts. Concerns about mine effects on caribou, fish, water quality, etc., have proven to be as predicted at Victor, or significantly less than expected, in every case.
De Beers has scheduled a bulk sample program for the Tango Extension kimberlite to be carried out in the first quarter of 2015. The results of this will be used to better understand the financial potential of the pipe. At that time the company will prepare a capital cost estimate for development that will include the pit and a surface buildings such as an office and lunchroom at the Tango Extension site. Resource tonnage, carats per hundred tonne numbers, and the value per carat will also be calculated when the results of the bulk sample are known.
Meanwhile a dewatering flow test is planned for March 2014. This will help determine the economics of dewatering the proposed new pit. These results will also be used to finalize the fixed costs, including the mining approach, for the project.
A spokesman for De Beers said that early indications are that the Tango Extension is not as economically viable as the Victor mine. The company will maintain its commitment, currently more than $50 million annually, to local communities. Whether that level of funding will be adjusted while mining the Tango Extension has yet to be determined, but De Beers remains focused on providing local priority for training, employment and business opportunities.
The Tango Extension environmental impact assessment is to be completed in July 2014. Mine dewatering is still being studied and comprehensive community consultations will be held. Given the timelines set out by the Canadian Environmental Assessment Act in 2012, De Beers expects a decision from the minister in mid-2015. If there are no major delays, a development decision may be made early enough so that financing can be secured and equipment mobilized for a winter 2016 start of construction.
The timeline is tight – three winters of construction at Tango Extension so that mining can start in 2018 before the Victor pipe is exhausted in the first half of that year. De Beers warns that any extended gap in the mining sequence between the two pipes will have a negative impact on the financial model for Tango Extension.
As the exploration of the Tango Extension kimberlite continues, De Beers may be prepared to develop Ontario’s second diamond mine.