Much of southern Saskatchewan is underlain by the Prairie Evaporite Formation, a layered sequence of salts and anhydrite which contains one of the world’s largest deposits of potash. The potash extracted from the predominantly sylvinitic ore has its main use as a fertilizer.

The 100 m to 200 m thick Prairie Evaporite Formation is overlain by approximately 400 m of Devonian carbonates followed by 100 m of Cretaceous sandstone, 400 m of Cretaceous shales, and 100m of recent Pleistocene glacial tills to surface. The Prairie Evaporite Formation is underlain by Devonian carbonates. The Phanerozoic stratigraphy of Saskatchewan is remarkable in that units are flat-lying and relatively undisturbed over very large areas.

Potash mineralization in this region of Saskatchewan is predominantly sylvinite, which is comprised mainly of the minerals sylvite (KCl) and halite or rock salt (NaCl), with trace carnallite (KMgCl3 · 6H2O) and minor water insolubles. Potash fertilizer is concentrated, nearly pure KCl (i.e. greater than 95% pure KCl), but ore grade is traditionally reported on a % K2O equivalent basis. The “% K2O equivalent” gives a standard measurement of the nutrient value of different potassium-bearing rocks and minerals. To convert from % K2O equivalent tonnes to actual KCl tonnes, multiply by 1.58.

Over the past three years (2018, 2019, 2020), the average measured potash ore grade of the mill feed at Vanscoy was 25.6% K20 equivalent. The average ore grade reported from 36 historic surface drillhole intersections, all within Vanscoy Subsurface Mineral Lease KL 114C, is 24.9% K20 equivalent (discussed further in Section 10.0). The average ore grade observed from thousands of in-mine samples collected to the end of December 2020 is 24.2% K20 equivalent.

There are three mineable potash members within the Prairie Evaporite Formation of Saskatchewan. Stratigraphically highest to lowest, these members are: Patience Lake, Belle Plaine, and Esterhazy.

The Vanscoy potash deposit lies within the Patience Lake Potash Member of Prairie Evaporite Formation. There are two potash seams named A Zone and B Zone within this Member; at present, only the A Zone is being mined at Vanscoy and no test mining has been carried out in the B Zone to date. Neither the Esterhazy nor the White Bear Potash Members are present in the Vanscoy area. The Belle Plaine Potash Member is not well-developed, and therefore is not mined.

Vanscoy potash mineralization occurs at approximately 1,000 m to 1,120 m depth below surface. The A Zone is approximately 3.35 m thick and occurs near the top of the Prairie Evaporite Formation salts. Salt cover from the ore zone to overlying units is approximately 12 m.

At Vanscoy, potash ore is mined using conventional mining methods, whereby:
- Shafts are sunk to the potash ore body;
- Continuous mining machines cut out the ore, which is hoisted to surface through the production shaft;
- Raw potash is processed and concentrated in a mill on surface; and
- Concentrated finished potash products (near-pure KCl) are sold and shipped to markets in North America and offshore.

Virtually all Vanscoy underground mining rooms are in one potash mineralized zone, the upper layer (or A Zone) of the Patience Lake Member of the Prairie Evaporite Formation (the host evaporite salt). At Vanscoy, mine elevations range from approximately 1,000 m to 1,120 m depth below surface. Mine workings are protected from aquifers in overlying formations by approximately 12 m of overlying salt and potash beds, along with salt plugged porosity in the Dawson Bay Formation, a carbonate layer lying immediately above potash hosting salt beds.

The Vanscoy mine is a conventional underground mining operation whereby continuous mining machines are used to excavate the potash ore by the stress-relief mining method. Continuous conveyor belts transport ore from the mining face to the bottom of the production shaft.

The highest mineral grade section of the Vanscoy potash seam is approximately 3.35 m (11’) thick, with gradations to lower grade salts immediately above and below the mining horizon. The actual mining thickness at Vanscoy is dictated by the height of continuous boring machines used to cut the ore which has been fixed at 3.35 m (11’). This mining height allows for comfortable working headroom and efficient extraction of potash ore.

Conservative local extraction ratios (never exceeding 45% in any mining block) are employed at all Saskatchewan mines, including Vanscoy, in order to minimize potential detrimental effects of mining on overlying strata; this is common practice in flat-lying, tabular ore bodies overlain by water-bearing layers.

From the shaft-bottom, potash ore is hoisted approximately 1,000 m from the potash level through the vertical shafts to a surface mill. In addition to hoisting potash ore to surface, the production shaft is used for exhaust ventilation from the mine and serves as a secondary egress. The Service Shaft is used for service access, primary egress, and fresh air ventilation into the mine.

The purpose of the crushing circuit is to prepare the ore for the downstream process by reducing the material size to 95% less than 9.5mm (-3/8”). This is the optimal size for the liberation of the salt and insoluble material in this ore body. Crushing and scrubbing will be accomplished in two stages.

The primary crush will be completed using a single stage of two parallel roll crushers after which the ore will be combined with saturated process brine to produce a slurry of optimal density for primary attrition scrubbing (two parallel banks of six 972 ft3 scrubbing cells). The discharge from the primary scrubbers is screened with the undersized (-6 mesh) material reporting to the primary deslime cyclones. Their overflow goes to slimes separation and the underflow to secondary scrubbing. The primary desliming screen oversize (+6 mesh) goes directly to secondary crushing which is done using one stage of three parallel cagepakors.

The secondary crushing discharge is returned to the primary scrubber feed for further insol liberation. The secondary scrubber (two parallel banks of six 444 ft3 scrubbing cells) discharge is sent to the secondary deslime screens with the undersize material (-20 mesh) reporting to the secondary deslime cyclones. The cyclone underflow goes to fines rougher flotation conditioning and the overflow goes back to the primary deslime screen feed. The secondary screen oversize (+20 mesh material) goes on to coarse rougher flotation.

The coarse rougher flotation circuit is required to maximize the production of coarse material and minimize the generation of finer material. However, in the tailings of the coarse rougher flotation circuit there is a significant amount of potash that isn’t sufficiently liberated. The regrind circuit is designed to recover this material by screening, crushing and re-floating the desirable potash from the coarse rougher tails. The flotation cells in this circuit use stepped banks to allow reagent conditioning at critical locations of the regrind process. The regrind circuit is a closed circuit as the regrind flotation tails are screened and recycling back to the feed. Only the regrind flotation concentrate and regrind eventually exit the circuit to re-cleaner flotation and the tails screen undersize go to the tails cyclones.

In recent years, the Vanscoy mine underwent a major expansion which brought the nameplate capacity up to 3.0 million tonnes of finished potash products per year. In 2020, operational capability at the Vanscoy facility was 1.7 million tonnes per year. Operational capability may vary during the year and year-to-year including as between our potash operations. [TR 2020, 31]

Slimes separation is required to remove the fine potash particles in the primary cyclone overflow from the unwanted insoluble material. This flow is passed over trash screens to remove larger foreign material that can impede the downstream process. The slurry that passes through the trash screens is sent to the inclined plate hydro-classifier to complete the slimes separation process. The current process uses insoluble (or slimes) flotation to achieve this step and hydro-classification has been proven throughout the potash industry to be a much more efficient and cost effective method.

Proper man ........