DIAMOND SPECIAL — Challenges await northern diamond-mine

State-of-the-art diamond exploration in Canada is currently directed towards a cluster of kimberlite pipes of economic potential discovered at Lac de Gras in the central Slave Province of the Northwest Territories.

Preliminary news releases indicate that several of the discoveries are of comparable diamond concentration, deposit size and gem diamond valuation relative to mines in southern Africa and Russia. However, several years of deposit evaluations and subsequent marketing negotiations lie ahead before an announcement of diamond mining in the Northwest Territories may be made. It should be noted that in the past, newly substantiated diamond mining regions saw production relatively quickly.

Based on the history of diamond mining in southern Africa and Russia, hundreds of kimberlite pipes remain to be discovered in the Canadian Shield. The great majority of pipes will not be economic but the incentive of finding multi-billion dollar deposits will provide for much exploration activity in the North for years to come.

Millions of hectares of land in the central Northwest Territories are receiving close scrutiny from the mineral exploration industry. New discoveries of deposits other than gem diamonds, particularly gold and base metals, are a reasonable expectation.

Should exploration be successful in outlining economic concentrations of gem diamonds at Lac de Gras, the opportunity of diamond mining would present itself to the residents of the Northwest Territories. Northern residents will judge any new mining development on the basis of protection of the environment and benefits to the Northwest Territories.

Some technical, environmental and health-related matters concerning diamond mining were found during the course of the review of available literature. These factors, as well as the challenges of climate, permafrost, remoteness and the lack of infrastructure, will need to be addressed in order for diamond mining in the Northwest Territories to become a reality. Environmental protection

Environmental considerations are important factors in the planning, construction, productive life and rehabilitation of any mine. Complying with environmental and conservation legislation is a vital element in current mine planning.

The current system of environmental review and approvals will handle the permitting of a new diamond mine. The physical properties of kimberlite, a comparatively soft, weak rock, may require assessment for mine safety reasons. The mining and processing of kimberlite may require further review of dust suppression measures if the mineral serpentine is present. A diamond mine processes kimberlite mechanically, not chemically. Due to the weak-to-moderate alkaline nature of kimberlite, the tailings would not be acid-forming nor contribute sulphide metals to mine drainage. Depending on the degree of alkalinity, kimberlite tailings may be chemically inert and not represent an environmental threat.

However, the environmental reviews performed for the mining of diamond-bearing kimberlite pipes elsewhere in the world may not be to North American standards and further studies may be warranted.

Infrastructure

Every large diamond mine in the world has road access and most have an airfield. Based on the present infrastructure in the North, a diamond mine in the Northwest Territories would be a fly-in/fly-out operation. In Yakutia, the Russians constructed a 750-km all-weather road linking all the diamond mines, new townsites and existing population centres to the port of Lensk on the River Lena. There are an additional 2000 km of winter roads in the Siberian diamond mining region which were used initially to develop the Yakutian mines and townsites.

The present Northwest Territories winter road system provides cold weather access to the communities of the Mackenzie River Valley and to the Lupin gold mine of Echo Bay Mines (TSE) near the Arctic Circle. The potential development of a diamond-mining region in the central Northwest Territories would initially require access to the deposit(s) from the Echo Bay winter road.

An all-weather road, in part supported by the presence of a major diamond-mining region, may be feasible when combined with other potential resource developments such as the nearby Izok base metal deposit. Ultimately, an 800-km road to Coppermine could be built. This road, in turn, would support other long term economic development.

As diamond operations generally require 3-to-4 times the yearly supplies than that of a typical gold mine, the present winter road may not be able to support such a volume of traffic. It has been suggested that extending the all-weather road to Mackay Lake would allow potential diamond mines to be resupplied via barge and winter road across Mackay Lake.

The preliminary cost for a 220-km permanent road from Tibbitt Lake to Mackay Lake would be close to $200 million. No single mining company or government could bear this cost.

Existing and potential power infrastructure in the Northwest Territories needs to be examined due to the presence of a potential diamond mine. A large diamond mine requires up to 20 megawatts of hydro- or diesel-generated power. The mine’s processing plant consumes the bulk of the power. A 20-to-40 megawatt hydro site could be developed and dedicated to a single, long-term mine, with the amortization (or cost of the investment) written off over the mine’s lifespan.

The development of a mining region with several producers, whether mining diamonds, gold or base metals, would support the development of a larger hydro power infrastructure. However, dependent upon the demand requirements and the dam site construction details, it could take 3-to-10 or more years to complete a hydroelectric project from concept to commission. The process of identifying and evaluating hydro sites in the Northwest Territories is under way.

Health hazards

Diamond mining uses basic principles applied by open-pit mining in general. The mining of kimberlite has never been scrutinized by health and safety authorities who, in North America, are focused on quartz mining (silicosis), uranium mining (radon gas), coal mining (coal dust and methane) and asbestos mining (asbestosis). Fortunately, kimberlite has little to no quartz or radioactive minerals.

Of concern as a potential health hazard is the fine-grained mineral, serpentine, which can be present in kimberlite. Asbestos is a type of serpentine. Russian research suggests that secondary (or weathered) serpentine is extremely fine-grained and exhibits fibre-or asbestos-like characteristics. Mica may also be present in kimberlite in the amounts of 1 – >50%. Mica has the same respirable dust threshold limit of 3 mg/m3 as soapstone.

Dust suppression measures may require review, as dust will be created from the mining, processing and tailings impoundment of kimberlite. Deep open-pit mining in Arctic climate

Deep, open-pit mines in Arctic regions exist only in Russia. Due to temperature inversions, carbon monoxide and other exhaust gases from operating machinery increase to unacceptable levels in the bottoms of their open pits. Permafrost is a fact of life at any minesite in the Far North. Permafrost enhances ground stability at the underground operations of the Polaris and Lupin mines in the Northwest Territories. The Russians, who have experience with open-pit mining in permafrost, have established the Russian Permafrost Institute, which could prove to be a valuable source of information on northern mining.

Mine safety

Slope failure at an open-pit diamond mine is not mentioned in the literature acquired to date. However, difficulties in ground control at South African underground diamond mining operations were noted.

Russian diamond mines also have the problem of toxic salt brines in groundwater and methane gas from petroleum fluids. The Russian kimberlite pipes occur in porous, oil-rich sedimentary rocks that overlay the Siberian Precambrian Shield. Salt brines and petroleum fluids are not anticipated from the present diamond exploration in the Northwest Territories, where the kimberlite pipes are restricted to the hard, dense rocks of the Precambrian Shield.

Pockets of high-pressure gas have been encountered by the Russians in the drilling and mining of kimberlite. It is not clear from the literature if they believe that their gas problem may be due, in part, to gases left unvented from the very gas-rich mechanism of kimberlite pipe emplacement, or due completely to the presence of petroleum fluids in the sedimentary country rocks.

Specific reference to gas pockets at the kimberlite pipe mines in South Africa and Botswana is not mentioned in the literature acquired to date. Mine discharges, tailings and waste rock dumps

The Russians have quantified the emissions and discharges from a large diamond open-pit mining operation, the values of which may or may not be typical for a large North American mining venture actively applying environmental safeguards. Further research is required.

The major volume of waste material produced by any large open-pit mining operation is waste rock plus tailings from processing. Waste rock at a potential Northwest Territories diamond mine would consist of Precambrian Shield rocks which, depending on its acid rock drainage characteristics, would probably require no special handling.

Kimberlite has a low content of sulphur and base metal sulphides. The tailings consist of kimberlite crushed to fine sand-sized particles with an infinitesimal amount of diamonds removed. No leaching chemicals are used in the milling circuit. Therefore, tailings are not acid-forming nor do they contribute significant toxic metals to groundwater and runoff. However, a study of the weathered, clay-rich caps of kimberlite pipes in Russia indicates that weak to moderate alkaline conditions prevail. Security

The theft of a single, large stone could significantly affect a diamond mine’s earnings. Diamond mining requires security to the extent experienced at high-grade gold mines or, perhaps, the Canadian Mint gold refinery in Winnipeg.

The only published details about diamond security measures are from the Orapa diamond mine in Botswana, which has a 3.2 km-wide “no-man’s land” perimeter. At the mine itself are a series of fenced and gate-controlled areas. The entire minesite is fenced. Access to the mill is controlled. The heavy media separation and diamond recovery area of the plant has additional security measures.

Security measures at an isolated minesite in the Northwest Territories would be focused on the diamond recovery area, controlling access to the minesite and guarding diamond shipments transported from the mine to the market. Diamond mines have armed guards plus strip and X-ray searches of personnel. Diamond is not touched by human hands during recovery at the processing plant. “Glove boxes”, used to sort the diamonds recovered at the minesite, are rubber gloves and arm gauntlets set in a plate of glass that separates the human sorter from the rough diamond.

The security measures required by diamond mining may result in changes in the legislation which governs regular law enforcement agencies.

— From a recent Government of the Northwest Territories publication.