THE JUST_IN_TIME MINE

By the time Anaconda decided to sell the Caribou, some 88,000 ft of drill core (an impressive amount by any standards) had defined a deposit consisting of six distinct lenses Each lens was deposited in succession some 400 million years ago, along with a sequence of interbedded phyllite, in an island arc environment on the western shore of the Iapetous Ocean The lenses have since been consolidated and draped around the nose of a relatively open fold which is now oriented so that its axial plane is near vertical A unit of weathering-resistant rhyolite tuff occupies the centre of the fold and forms the hangingwall of the deposit The entire deposit totals some 60 million tonnes and is 35 m wide in places Anaconda originally wanted $5 million for it and Cavalero had to put together all the geological data in an information package suitable for buyers who wanted to take a close look at their work He accomplished this, but only one offer came in Not that it was his fault; the market for base metals was dismal at the time and Anaconda didn’t make a buck when it mined some 340,000 tonnes of supergene-enriched copper from the top of the deposit, and so the Caribou acquired a notoriously poor reputation among Canadian geologists That made it a difficult sell

Two Australians — metallurgist Richard Watsford and chemical engineer David James — took a closer look at the data Going back to fundamentals, they recognized (almost immediately, according to Watsford) the potential of the primary mineralization below the supergene zone that Anaconda had mined in the 1970s Their company, East West Minerals, quickly offered Anaconda $1 million for the Caribou deposit in May, 1986 Anaconda said it wanted to advertise the sale first, so the offer stood until December, 1986 One other offer was made, but that company wanted a 5-month option to examine the property East West made a counter-offer for a 3-month option and agreed to assume responsibility for Anaconda’s open-pit mine wastes in exchange for a 100% interest in the property and five other base metal deposits discovered by Anaconda in the Bathurst camp (Two of these deposits were the Armstrong A and B deposits to the east ) Under pressure to sell by the end of December, Anaconda accepted East West’s offer That was good news to Cavalero East West needed a geologist who knew the deposit, and with Anaconda now defunct, Cavalero was moving his family around the continent trying to nail down a long-term job He is one of only six East West employees who were with the project when it was operated by Anaconda

Today, Caribou is very much a Colin Smith project Smith was one of four experienced managers whom East West brought north from Australia in order to get the mine and mill up and running Today he is general manager in charge of the entire operation With a tight 5-month schedule, Smith likes to work his people flat out “There have been times when we would start things up on a leap of faith, without actually knowing that everything was ready to go,” he told The Northern Miner Magazine The organizational structure at the mine is flat, too There are no multiple layers of management through which employees have to go to obtain approval for a project Regular meetings keep everyone informed on the overall progress of the project and employees take the necessary action to meet objectives This way, employees take personal responsibility and satisfaction for their actions

“In Australia, we have problems with contractors,” mine engineer Dave Edwards explained “But here, we can’t say enough about the spirit of co-operation, even though we’re under a lot of pressure to get the mine going There has not been an argument to hold things up I find that, no matter how busy people are, they’ll stop to help each other out ”

Pre-production development was coming to an end when The Northern Miner Magazine visited the site in November At that time, Smith was confident the new 2,000-tonne-per- day mill would produce the projected 126,000 tonnes of lead/zinc concentrate in 1989 And confidence was high that the company would be able to do it at an overall cost of about $35 per tonne of ore mined Smelter penalties will be about $47 per tonne mined and mining will be at a rate of 700,000 tonnes per year

The work index of the ore (which is a measure of how much energy is required to grind the ore to a particular size) is very low (12 to 13) and fragmentation is good, said mill manager Steve Williams So energy-intensive crushing is unnecessary That should help keep down costs Run-of-mine ore is fed into a semi-autogenous grinding mill, the lead and zinc are recovered by flotation, and concentrates are thickened and then dried in an automatic filter press

An example of the confidence with which East West is proceeding with this mine can be seen underground All the original mine openings that Anaconda drove in the 1960s and ’70s (a ramp and drifting on two levels, spaced about 119 m apart) had to be slashed to accommodate the larger scoops and trucks East West is using to haul ore to surface up the 20% decline That meant all the survey plugs in the back were brought down And yet by tying the new plugs back into the original grid, surveyors have successfully directed miners with pin- point precision Of the two 6-ft fill raises driven by raise-bore machines, all broke through at the desired location, saving valuable time and money chasing pilot holes Mind you, the raises were only 60-85 m long, yet any mistake would have been costly

At the time of our visit, pre-production work was coming to an end Crews had silled out three cut-and-fill stopes on the 2,365-m elevation (150-m depth) and were working on two more That should be enough stopes to produce the required 2,000 tonnes of ore needed each day to keep the mill running at capacity, said Mine Engineer Dave Edwards About 75% of those tons will come from the east limb of the deposit “We’ve mucked out a round at a rate of 250 tons per hour using 5-cu-yd scoops and three 30-ton dux trucks,” Edwards said The mine will be working flat out — seven days a week, 24 hours a day Because of the bands of interbedded phyllite in the ore, Edwards, who is on consignment from Z C Mines at Broken Hill, Australia, believes it is necessary to have a mining method which allows geologists to examine each face and which permits miners to selectively mine the ore and waste “If we can identify waste, we’ll handle it ” The flexibility of cut-and-fill will allow miners to chase high-grade zones, too But that’s not to say the mine will always be a cut-and-fill operation Bulk-mining methods may eventually be used in the wider portions of the orebody, Edwards explained

East West has decided to mine the high-grade zone which extends from the hangingwall contact and grades progressively lower toward the footwall At a cut off grade of 12% combined lead zinc, mining widths range from 1 m to 10 m Average widths are about 4 m (The average ratio of zinc- to-lead is abou
t 2 7:1 ) Edwards says they will be able to take three 3-m lifts in each stope before the equipment becomes captive in the stopes Three scoops with 3 1/2 cu-yd buckets will be used in the captive stopes Two will be electric and one diesel

Three Eimco-Jarvis-Clark 1-boom jumbos will be used to drill off the lifts Each lift will produce about 25,000 tons of muck, he estimates Ore will be mucked from the bottom of the mill holes with four 5-cu-yd scoops loading 30-ton DUX trucks

“There was no evidence of stress- related problems when Anaconda did their feasibility study,” Edwards said, “and we don’t expect any in the upper levels ”

A third level will not have to be developed until late 1989 At that time East West will evaluate the need for a 10-m pillar between levels A 15-m pillar will be left between the open pit and the underground workings Plans are also in the works for a new shaft which would be driven in the rhyolitic tuff hangingwall for hoisting ore from deeper levels in the mine The lifetime of the mine is expected to approach 20 years

As part of the deal with Anaconda, East West has agreed to deal with the problem of mine drainage waters which contain toxic levels of soluble metals and which are highly acidic The run-off comes from the mineralized waste rock and tailings dumps from Anaconda’s mining activities which ended in 1975 East West’s approach to environmental protection represents more than just lip service Fish habitat, lost by construction of the 100-ha tailings disposal area, will be replaced by installing a pond upstream of the tailings disposal site and by careful layout of the diversion ditch so as to provide a suitable habitat for fish

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