Rocanville Potash Mine, Saskatchewan, Canada

The Rocanville potash mine is 16km north east of Rocanville and approximately 200km east of Regina, south-east Saskatchewan, Canada. Wholly owned by the Potash Corporation of Saskatchewan Inc. (PotashCorp), it has a capacity of 3Mt/y of potash products (KCl). Its output of 2.57Mt of KCl in 2005 was markedly up on the 1.83Mt that was achieved in 2004, as the first stage of a nominal 400,000t/y expansion came on stream. Planned in response to growing agricultural demand, especially in China, the expansion actually achieved an increase in capacity of 749,000t/y. The mine produced 7.5Mt of ore grading 24.7% K2O during 2005..

GEOLOGY AND RESERVES

The potash zones are sandwiched between rock salt formations within the prairie evaporite. The lower esterhazy member is mined for potash. The primary lithology is halite with variable amounts of sylvite, carnallite and clay. The main ore zone occurs at a depth of approximately 960m.

The average thickness is 2.43m with an average grade of 21.5% K2O and 1.4% insolubles. At the end of 2005, PotashCorp stated Rocanville’s reserves as being 372Mt at 22.5% K2O, sufficient to support production at current levels for 59 years. The overall inferred resource for the mine is 1,132Mt.

MINING

The mine has two concrete-sealed, 1,000m-deep shafts for production and service within the Blairmore formation.

Rocanville uses a long room-and-pillar method of mining. Ore is mined from rooms in three passes, separated by pillars supporting the overlying strata. Five automated Marietta two- and four-rotor continuous miners, each capable of extracting 650t/h of ore, form the production fleet. The run-of-mine ore is loaded on to extensible conveyors attached to the continuous miners. These connect to the main haulage conveyors, which move the ore to skip-loading pockets at the shafts, where it is hoisted to surface.

In addition to automating its Marietta miners to measure ore grades and mine selectively, the company installed a central control room at Rocanville from which the entire mine, surface and underground, is controlled. The central control system, supplied by Allen-Bradley, oversees all aspects of the mine and mill operation, and has maximised ore extraction and recovery since it was commissioned.

Rocanville recirculates a proportion of its ventilating airflow in order to reduce heating costs in winter.

ORE PROCESSING

The run-of-mine ore is crushed to free the KCl (potash), and is scrubbed and deslimed to remove any clay. After conditioning with reagents, the potash minerals are floated off with the products then being de-brined, dried and screened before shipment.

The mill has a central control system which monitors the ore throughout the refining process. Run-of-mine ore is dry-crushed and screened in a two-stage circuit before being slurried in a saline solution together with the fines prior to pumping to a sizing screen distributor. Mill feed is then de-slimed in a circuit of three scrubbing tanks for stationary screening, hydroseparating and thickening. Carnallite is decomposed in a cool leach stage. Feed for reagent addition is collected from the stationary screens and cyclone underflows and is treated in vertical conditioners before being combined in a bulk flotation process. In the coarse flotation circuit, the ore treated with reagents is fed into a series of rougher, cleaner and recleaner flotation cells.

Final mill tailings are drawn off at the rougher stage and final product at the recleaner stage. Cleaner-cell tailings are recycled to the rougher feed and recleaner tailings thickened in a scavenger cell and used as crystalliser feed. The product is dewatered in centrifuges before drying in gravity-fed, direct-fired driers and classified according to size (granular, coarse, standard and suspension). Rocanville has the capacity to produce 2.695Mt/yr of granular, coarse and standard agricultural-grade potash, as well as industrial-grade material, and produced 1.83Mt of KCl in 2004. Having just expanded Rocanville's granular-product production capacity by 400,000t/yr, PotashCorp has now committed US$80m to a 500,000t/yr expansion of the operation's product-compaction capacity.

TRANSPORTATION

Most Rocanville potash travels on Canadian National and Canadian Pacific railways for domestic sales and transfer to ports. Overseas sales are exported by the potash-producers’ marketing company, Canpotex, from the West Coast, Great Lakes and Gulf of Mexico. Road transport is used for local and upper Midwest US deliveries.

ENVIRONMENT

During 2000, around 1,420ha of land at Rocanville were transferred into the Saskatchewan Representative Area Network, containing areas of untouched ecosystems.