Potash mine gets a boost
A decade ago managers peering out the office window at Penobsquis mine in Sussex, New Brunswick would have been pleased by all the activity outside. For years a world-wide glut of potash had driven potash prices into the basement of the commodities market; now those prices were staging a comeback, so much so that PotashCorp Saskatchewan (PCS) purchased the Penobsquis mine, mill and port facility as part of a larger US $112 million transaction from Rio Algom. The future looked promising.
That future looked even brighter, says Stewart Brown, because of what lay about a kilometre beyond the Penobsquis mine. “There’s was always an understanding that there was probably potash mineralization across the highway from the existing mine,” PotashCorp’s project manager says looking out the same window in 2013. “But during drilling for natural gas in 2000-01, the extent of the ore zone became more evident.” By the mid-2000s seismic studies revealed a delineation of potash thicker and flatter than the Penobsquis property, lending itself to something other than the hard rock mining approach at the Penobsquis mine.
“The ore body at Penobsquis dips at 50-60 degrees so we use cut-and-fill mining here to extract the ore.” By contrast, the ore body at Picadilly is flatter and features twinned, parallel access drifts, established in salt below the ore zone that extend eastward from two vertical, concrete-lined shafts. These provide access, through cross-cuts, to the evaporite area where potash deposits are located. “We will cut straight ahead for the better part of a kilometre, turn around, widen the drift, go down and cut the floor over the same distance, then widen that out.”
The result, says Stewart, should be an excavation approximately 12 metres wide and 20 metres high and an increase in production at Picadilly that will more than double the 750,000 tonnes of potash PCS currently sends through Barrack Point potash terminal in Saint John. “Our operational capability from Picadilly is going to be 1.8 million tonnes of potash per year.”
Water, water everywhere…
To set the stage for all that additional potash production, PCS first had to address the nemesis nearly every potash operation faces: water. Water is a necessary part of the brine process in potash mining but in 1997 excessive brine proved the undoing of PCS’s Cassidy Lake mine about 50 km from Sussex when it flooded and was lost after 10 years of operation. Today, Brown says, PCS spends “a significant amount of money” on drilling and grouting to manage an inflow at Penobsquis of about 1,200 gallons per minute. “It’s kind of like the little Dutch boy with his finger in the dyke; you could seal one crack and it comes out another crack.” Adds Brown, that inflow could increase once grouting operations stop at Penobsquis and Picadilly is up and running. Two decisions were made that will avoid that scenario.
The first came during an earlier construction stage when PCS ruled out as ‘too expensive’ the use of vapour recompression evaporators to rid Penobsquis and Picadilly of excess brine. Instead it built a 30-kilometre brine pipeline to ship excess brine from the Penobsquis mine site to the company’s brine pond at Cassidy Lake and into the Bay of Fundy. This lowered the daily volume of brine hauled away to less than half the 2008 volume.
The second decision, Brown says, was to not connect the two mines in order to shield Picadilly from the brine inflow that occurs the day Penobsquis mine closes and is permitted to flood.
“If we connected Picadilly to Penobsquis and the flow increased, we could potentially impact the Picadilly Mine. We don’t want the mine to flood.”
The brine pipeline was an important first milestone. The second milestone occurred in 2011 with the construction of the head frames for the 900 metre production shaft. “We knew the project was going to go ahead,” Brown stresses. “This is not an exploration project. This is going to be a producing mine.” Within days, Brown’s crew had driven piles down to solid rock and removed the overburden before laying the concrete floor to support the head frames. PCS also decided those head frames would be permanent rather than temporary: a permanent head frame not only saves time, says Brown, “It provides a lot more efficient transition to permanent hoisting than a temporary head frame.”
The head frames at Picadilly went up quickly, over two and a half weeks. Once the head frames were in position, crews installed hoisting equipment to sink the shafts. Here’s where some of the tougher work occurred, says Brown. For one thing, underground conditions didn’t entirely match the geological model grouting crews had been expected to work to. The main obstacle: anhydrate. “Mining machines can cut in salt and in potash but anhydrate is more of a limestone type feature that is a harder rock that mining machines can’t cut. So we drill and blast.”
As the drilling and blasting proceeds, a concrete liner is installed from behind. “So at the end of the day a circular shaft is in place, reinforced with concrete anywhere from two to three feet thick.”
Throughout construction, PCS had its eye on one target: to produce enough granular potash to meet world markets. By the summer of 2011, both pairs of 100-metre high concrete head frames for the production and services shafts as well as a brand new compaction plant had given the company what it wanted – the ultimate ability to produce 1.5 million tonnes of granular potash to meet those markets, notably in Brazil’s potash-hungry agriculture sector.
“Brazil is a huge consumer of granular product used in mechanized farming,” Brown says. “So here in New Brunswick, 85 per cent of our production right now is granular product and 15 per cent is standard product that goes to Cuba, for example, where potash is spread manually.”
Equally important, says Brown, will be the ability to change the ratio of granular to standard potash as the demand for both types of potash fluctuates. Picadilly will give PCS that flexibility.
That most valuable of resources…people.
It was one thing to increase capacity at the production and service shafts, as well as at the compactor operations, but just how big a construction fleet did PCS need to build all that?
“Huge,” replies Brown, none more extensive than the fleet of mobile cranes supplied by Irving Equipment. “I think we had every manufacturer of some sort of crane over there,” he chuckles. From rubber-tired mobile cranes and smaller man lifts and scissor lifts designed and manufactured by firms like Genie, right up to giant Manitowoc and Liebherr cranes.
“Some of the longer term installations had the big 600 tonne crawler mounted cranes for putting up the tanks for example. And as the project got a little more complete we had the 200 tonne cranes that come down the highway from Saint John to lift pumps, structural steel etc. and then go back to Saint John.”
In addition to the cranes, another plus, says Brown, was Irving’s ability to supply the talent. Unlike PCS’s new potash shafts in Saskatchewan where labour is sometimes in short supply, skilled trades are plentiful in New Brunswick, in large part because the economy is hurting and skilled trades are eager for work. In fact, outside of the Nuclear Generating Station refurbishment in Point Lepreau, PCS’s potash operations at Penobsquis and Picadilly represent the largest construction project in the province. A far bigger challenge has been bringing in new hires for the actual mining operations at the mill and underground.
“We’ve bought mining machines for our Picadilly project that have never been used in North America. For example, we have six Sandvik MF420 twin rotor mining machines and four Sandvik MB670 drum miners and in the past year, our focus has been working with some of our employees training them how to operate and maintain these machines.”
In 2008, PCS employees at Penobsquis numbered 370. By the time Picadilly is up and running next year, a staff of 500 will have risen to more than 600. Some of them are already hard at work installing hoist ropes and permanent conveyance systems in the service shaft. “And as we finish that, we’ll start on the change over at the production shaft and we would hope to have permanent hoisting there in early 2014.”
As impressed as Brown is by the scope of the project and the technology brought to bear at Penobsquis and Picadilly, he reserves most of his praise for the people. The enthusiasm for working on a new mine is contagious, he says, driven by an entirely new generation of miners in New Brunswick. “They’re stepping up and putting in that extra effort to bring it on line. It’s pretty gratifying.”
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