Pushing for Potash

Back in 1981, all the signs for Saskatchewan’s potash industry looked good. Prices were high, the worldwide demand was increasing, and never had the government of Saskatchewan been more bullish about its massive potash reserves.

And then the bottom slowly fell out. Over the next decade, demand for potash slumped; the Soviet Union, a world producer of potash, collapsed, dumping the 12 million tonnes of potash it produced each year onto world markets. Potash prices fell. Mine development ground to a halt.

Scroll forward 30 years and the excitement around Saskatchewan potash is returning. Soviet potash has long since worked its way through the market. Potash prices are once again soaring (approximately $400 per tonne, or four times the price in the late 1990s) and world demand for potash is about 55 million tonnes a year and increasing each year by three per cent. That brings with it a different problem: the need for an additional 1.5 million tonnes of potash each year, and too few potash mines to meet the added demand. It all spelled trouble for potash producers, says Steve Fortney, General Manager of Potash Corporation of Saskatchewan (PCS).

“There was surplus capacity in the marketplace for a long time, then mines were underutilized. Today we’ve got to the point where all of the slack in that system has been taken up generating real shortages of potash in the world.”

Thankfully, part of the answer to those shortages can be found at Scissors Creek in Rocanville, Saskatchewan, where PCS is undertaking one of the most ambitious and complex potash shaft drilling projects in the world. When it’s finished in 2013, the new, six-metre-diameter shaft will plunge more than 1,100 metres beneath the earth delivering personnel and supplies to the production area. At $2.8 billion, it is the first potash shaft to be drilled in Saskatchewan in over 30 years – testing PCS’s technical expertise, says Fortney, and ultimately benefiting the entire potash mining industry.

“The re-emergence of the technology and the knowledge base to sink shafts is very exciting. And we were the first. The rest of the shafts sunk in the industry will be sunk in the same mould as ours and the expertise that we’ve rekindled in this project will be floated throughout future projects.”

That sinking feeling…

Fortney says it’s not just a dearth of shaft development that has been lacking at the Rocanville site, but a lack of information about its geology. Anyone who’ d worked on the first shaft in 1981 had long left the scene. Pouring through old records the first thing geologists and engineers discovered was that of the 17 shafts sunk in the 1970s, seven were flooded.

A pilot hole soon confirmed what they suspected, that water fed by a local lake had entered the Scissors Creek site mixing with sand in a 425-600 metre zone below the surface subsequently dubbed the Blairmore Formation.

“What amazed me the most,” says Arnfinn Prugger, PCS’s Vice-president of Technical Services, “is that you can have sand at 600 metres depth and it is a sand like you would find on a beach.” That mixture of sand and water also became an immediate hazard because of the enormous pressure within the shaft.

“Imagine you are 600 metres below the surface and you have 600 metres of water pressure against the wall of your shaft. That means the lining of the shaft has to be designed to withstand that water pressure.”

“And you can’t grout it,” adds Fortney. “So what we did is drill 32 holes around the perimeter of the shaft and freeze the entire area down to 600 meters. Once we froze that zone we could sink the shaft. When we’re done, a steel lining and a chemical field keeps the water out.”

Freezing calcium chloride brine required temperatures as low as minus 35 degrees Celsius, all of it injected into the freeze ring before the actual shaft pre-sink could begin in 2010. The next stage was a platform set-up for a series of grouting curtains, to drill into the shaft’s limestone formation and then seal that off with grout and cement. After that, tubbing rings are installed to secure the shaft lining. “Once we get close to the potash level there’s several metres of salt that are water free,” says Fortney.

Shaft sinking at Rocanville’s Scissors Creek site has seen immense improvements since the last shaft was built in 1981. For one thing, concrete is stronger and better castings for tubbing have improved shaft liner design.

“Even the grouting process has gone through a big improvement,” says Roy Durr of Associated Mining Construction (AMC) of Regina, a joint venture between J.S. Redpath and Thyssen Mining. “The biggest concern,” he adds, “is always safety.

“In the old days you would have a serious accident almost every two to three weeks where now that is unacceptable. Today, the technology is geared towards both the environment and safe working conditions.”

Working top and bottom…

With world demand for potash increasing at an estimated 12 million tonnes over the next eight years, the premium is on building more potash mines and building them quickly, particularly here at the world’s largest and most lucrative potash site.

One way PCS increased the pace was to construct a permanent head frame above the mouth of the new shaft. Typically a temporary head frame is built over the shaft, then torn down and a permanent head frame constructed; PCS went with a permanent structure, says Roy Durr, to save valuable time “because while you’re waiting for the freeze wall to form you’re actually doing some surface construction.” This was done, explains Arnfinn Prugger, by building a system of piles and pile caps outside the diameter of the freeze ring on which massive concrete beams were poured.

“We put the permanent head frame on top of all that, so the head frame is essentially on ground. In the long run, it’s quicker and cheaper going to a permanent head frame rather than building it twice.”

Meantime, attention is also being paid to increasing actual production at Rocanville through conversion of an original service shaft 16 kilometres away into the second of two production shafts. According to Fortney, this involved constructing a new head frame over top of the existing service head frame, deepening the shaft and installation of production bins. “It’s a slightly different technology,” he explains, “because we only had to deepen it a hundred metres and we didn’t have to go through any water-bearing regions.”

A piece of cake compared to the new service shaft, adds Fortney. Seldom has a project generated as much interest or curiosity about potash mining. “There were rumors about how to sink the shaft but not a lot of facts and no-one to really tell you for sure how it was done.”

Arnfinn Prugger agrees. Everyone (engineers, project managers and builders) was preoccupied by the particular challenges that both water and an ambitious project schedule presented at the mine site.

“It was a lot of work for many people, but I find it interesting and exciting to be into this new territory. I think my workmates do as well.”