Where the Waste Went

It’s been more than 80 years since minerals were first discovered at Prairie Creek in the Northwest Territories and over that period of time, many miners have come and gone in their quest for riches from this remote site.

Located almost 1500 kms north of Vancouver in the Mackenzie Mountains, Prairie Creek has been the focus of on-again, off-again mining activity since 1928. Much of the work was done on a small, part-time basis and it wasn’t until 1966 when Cadillac Explorations Ltd, of Vancouver literally ‘bulldozed’ its way in, that a determined effort was made to develop the site for all its worth.

Dozers were initially used to trench and cross-cut three mineralized zones (known as Zones 3, 7 and 8) and as it was always believed, Prairie Creek proved to contain a bountiful resource of prized minerals, including, lead, zinc, silver, and diamonds!

As already mentioned, many players have shown interest in the Prairie Creek mine over the years and the information on page 23 gives an overview of what’s happened from when Cadillac Explorations Ltd. started making headlines back in 1966 to now when Canadian Zinc Corporation of Vancouver is hoping to make the Prairie Creek Mine live up to its full potential.

As every mining company knows, there’s far more to mining today than simply extracting minerals from the earth. Aside from the pure economics of putting a shovel into the ground, miners today face a number of new challenges, not the least of which is getting all of the necessary operating permits and various other local approvals to go ahead with the job.

For Canadian Zinc, it’s been an exhausting task but the company has just announced that it has moved one step closer to putting its Prairie Creek Mine back into the headlines thanks to recent developments with federal, provincial, and local authorities.

Like many mining operations, one of the major concerns by all parties is for the safety of the environment and Canadian Zinc is proud of the work it has done to help ensure that all issues and concerns are met in order to get its Prairie Creek Mine back in business.

One of the first of foremost concerns for the safety of the site involved the removal of more than 40 tonnes of sodium cyanide that had been stored on the property since 1982. It was originally brought to the site between 1980-82 by the site’s previous owner and although safely stored in steel containers, Canadian Zinc determined they wouldn’t need the cyanide for any future milling uses so they decided to remove it entirely from Prairie Creek.

Given that sodium cyanide is a potentially dangerous chemical to handle and transport, Canadian Zinc hired Hazco Environmental Services of Calgary to design and execute a removal program rather than try and do the job themselves.

Under the direction of Project Manager Bill Durnford, Hazco developed a plan whereby the 852 drums, each containing 50 kg of 94% sodium cyanide, would be flown from the remote Prairie Creek site in a twin-engine Buffalo aircraft to a staging area at Fort Simpson, from where it would eventually be shipped by Hazco trucks to a destination in Barrie, Ont. for its final disposal. Initially the plan was to truck the cyanide off the site over a winter road but a delay in a permitting process for the road led the company to use the aircraft.

It took 11 trips to fly all of the cyanide from the mine site to Fort Simpson but as Durnford explained, a lot of work had to also be done before making the flights to ensure the chemicals were safely contained.

As mentioned earlier, the cyanide had been sitting at the mine site for nearly 28 years and over those years, the steel containers had started to weaken. Both Hazco and Canadian Zinc agreed the containers were still safe but to further ensure the chemicals remained intact during transport, Hazco technicians repacked the original drums in new steel drums with a UN rating appropriate to contain the chemical for transportation.

Bill Durnford said that in addition to securing the cyanide in new drums, Hazco’s team consisting of Safety Officer Rob Watt and Waste Technicians Norm Watwood, Stefan Radzichowsky, and Gord Kyllo worked with Canadian Zinc’s Safety Team to create a Job Safety Analysis, Safe Work Plan, and Site Specific Emergency Procedures before the move started.

Hazco and Canadian Zinc also produced an Emergency Response Assistance Plan (ERAP) for approval by Transport Canada before the air lift took place. With everything approved for transport, the drums and all tarps and pallets that may have come in contact with the cyanide were cleaned and also packed for shipping from the site. The tarps and pallets were incinerated at a treatment facility in Swan Hills, Alberta.

Once in Fort Simpson, the drums were loaded onto trucks and shipped across country to Cyanide Destruct Systems Inc in Barrie, Ont where General Manager Andrew Harvey and his team were awaiting their arrival.

Mr. Harvey told Canadian Mining Journal that the Canadian Zinc shipment was the largest drum load his company has ever handled, but like other chemical shipments of a similar nature, great care was taken to ensure the contents of the drums were disposed of safely.

“Cyanide loads received at our facility are tested for acceptance criteria. Each customer shipment is assigned a lot number and drum lots are also dated. Specific to the Canadian Zinc load, the cyanide drums were removed from the overpacks and skidded for staging through the process,” said Harvey.

“Drums are cut open and the cyanide is dissolved in a primary tank. Due to the fairly high cyanide concentration, we run about 10 to 15 drums per day. All cyanides are fed into a raw storage tank. The tank is the feed for thermal hydrolysis reactors that destroy the cyanide wastes. This simple, naturally occurring chemical reaction is accelerated dramatically by using elevated temperatures and pressures. This chemical and chlorine-free process guarantees complete destruction of all cyanide complexes, even iron. Canadian Zinc’s drums were mixed in with other cyanides in this tank to dilute the concentration. The process from heat up to cool down is approximately eight hours,” explained Harvey.

From the Mackenzie Mountains in the Northwest Territories to the shores of Lake Simcoe where CDS Environmental Services is located, the sodium cyanide from the Prairie Creek Mine site has been on quite a journey.

A journey, however, that clearly serves to illustrate one mining company’s concern for the environment. Cost to dispose of the 40 tonnes of sodium cyanide was $300,000.00.

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What’s in the Ground

The partially developed underground Prairie Creek Mine, with its 1,000-ton per day mill and related infrastructure and equipment already in place, hosts a major mineral deposit with a Measured and Indicated mineral resource in the Vein and Stratabound deposits of 5.2 million tonnes grading 11.4% Zn, 10.9% Pb, 176 g/t Ag, and 0.3% Cu along with an open-ended Inferred resource of 5.5 million tonnes of 13.5% Zn, 11.4% Pb. 215 g/t Ag, and 0.5% Cu. (Technical Report NI 43-101).

Potential for increases in both Vein and Stratabound mineralization also exist throughout the property. The farthest hole to the north on the mineral resource intercepted identical veintype mineralization in the same stratigraphic/structural setting as in the underground workings indicating the vein remains open to the north.

The southern part of the property contains numerous exposures to veintype material in identical geological settings to that found in the main zone. Some wide-spaced exploration drill holes have also returned stratabound type mineralization over 3 kms south of the defined mineral resource at the mine.

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An historic look at what’s been happening at the Prairie Creek site

In 1970, the Prairie Creek mine property was optioned to Penarroya Canada Ltd. of Vancouver for underground development of Z
one 3. Bulk sampling and preliminary metallurgical test work was done and some surface drilling was carried out on Zones 7 and 8.

• In late 1970, Cadillac terminated the agreement with Penarroya and between 1970 and 1980, extensive underground work at Zone 3 at the 930 m and 870 m levels took place.

• In 1980, Cadillac bought a 1,000-ton per day concentrator and by May 1982, the surface facilities at the site were 90% to 95% completed and mine preparation work to produce an initial 500 tons per day had been finalized. A total of CDN$64 million had been spent on the mine.

• Like today, mineral prices collapsed and Cadillac was forced into bankruptcy.

• From 1982 to 1990, the property was tied up in litigation, until…

• In 1991, Conwest Exploration Company Limited of Toronto bought the property and granted an option to Canadian Zinc Corporation of Vancouver, (then known as San Andreas Resources Corporation) to acquire a 60% interest in the property. Since then, Canadian Zinc has completed 40,000 m of surface diamond drilling and an underground exploration program. In 1992, the discovery of the stratabound-type mineralization in the main zone opened up multiple exploration targets for both vein and stratabound deposit expansion.

• In 1993/94, in addition to diamond drilling, the company also completed initial environmental assessment research and further metallurgical studies.

• A 1995-drill program explored for the extension of the vein to the north on 200 m step-out sections. The vein now has a strike length of 2.1 km and remains open at depth.

• In 1997, underground workings were rehabilitated in order to complete detailed chip sampling of the vein at the 930 m and 870 m underground levels.

• In January 2001, Canadian Zinc completed a Scoping Study designed to outline and guide the re-development of the mine and mill. Cost then was estimated to be CDN$40.5 million.

• From 2002 through 2005, the company focused on everything from further exploration and development, to designs, to applying for and securing Land Use Permits and other approvals.

• For the past three years (2006-2008), Canadian Zinc has continued with the development of the Prairie Creek mine, including surface and maintenance exploration and development.