Sussex (Penobsquis)

Overview

PotashCorp owns and operates a potash mine in Sussex, New Brunswick, Canada. Production at the Penobsquis mine started in 1986. The mine was acquired by PotashCorp in 1993.

Geologists inferred the existence of potash deposits in Atlantic Canada as early as 1840. It wasn't until the early 1970s that a jointly funded federal-provincial drill program made a landmark potash discovery near Sussex.

Potash is a general term covering several types of potassium salts, of which the most important is potassium chloride, the mineral sylvite. Potash is a nutrient essential for plant growth, and is a cornerstone of modern agricultural fertilizers. Roughly 95 per cent of world potash production goes into fertilizer, while the other five per cen  is used in commercial and industrial products - everything from soap to television tubes.

Sussex/Penobsquis is an underground potash mine that employs high productivity cut-and-fill  mining methods with the help of continuous miners. Potash is processed by crushing, flotation and crystallization methods. Over 95 percent of the product is shipped by rail to the company's potash terminal at the Port of Saint John for export. Canada is the world's leading producer and exporter of potash.

Location

The mine site is located 8 km (5 miles) east of Sussex, New Brunswick, Canada on the north side of the Highway No. 114.

New Brunswick is a Canadian Maritime province that is constitutionally bilingual. Fredericton is the capital and Saint John is the most populous city.

The province's economy is mostly modern but forestry, mining, farming and fishing are still important components.

Geology & Mineralization 

Throughout Atlantic Canada, potash mineralization of economic significance is restricted to Early Carboniferous marine evaporite deposits of the Windsor Group i.e. in the Visean rocks.

The evaporites formed in a Late Devonian to Early Permian Maritimes Basin. This basin developed over an area of nearly 75 000 sq km in the wake of a series continental collision events terminating with the formation of the Appalachain Mountain chain. The basin formed in northeasterly trending horst and graben structures.

Several episodes of faulting and folding have affected the strata of the Maritimes Basin. In and near deformed regions, evaporites are complexly folded into isolated diapiric structures, salt ridges or walls.

Potash is a naturally occurring mixture of mineral silvite (KCl) and salt rock or halite (NaCl).

The potash ore zone is found on the north flank, of a salt-cored anticline extending 25 km to the northeast. The ore zone, which varies from less than 10 m in thickness to over 100 m, is presently mined at depths ranging between 400 m and 760 m. The ore zone's steep dip, together it's with variable strike and thickness, dictate a flexible mining method for quick, efficient resource recovery.

The potash at Sussex is a mixture of 38% sylvite and 60% halite, with an insoluble fraction, up to 2%, composed mainly of clay minerals and sulphate.

Mining & Operation

The potash mining horizons, which are between 400 to 700 meters (1,300 to 2,300 feet) below the surface, are located on the flank of an elongated salt structure.

Underground mining operations take place at a depth of between 400 and 700 meters.Two vertical, 600 m long, 5 m diameter, concrete-lined shafts access the salt dome. Twinned, parallel access drifts, established in salt below the potash ore zone, extend eastward from the shafts providing access, via cross-cuts, to the evaporite area where potash and salt deposits are located.

Stopes are developed both above and below the access drifts and can be several hundred metres long, varying from 24 m to 61 m wide and up to 6.7 m high.

The ore is cut by continuous mining machines utilizing a cut-and-fill mining method. This method allows for a high extraction ratio while providing excellent ground conditions. Where the deposit exceeds a width of 40 m, pillars are developed to assist in the support of progressively higher excavation.

The mined potash ore is transported by conveyor belt systems to a storage bin at the main shaft and hoisted 580 meters (1,900 feet) to the surface for processing.

The rock salt located in the core of the salt dome structure is also extracted by continuous mining machines using a multi-level room-and-pillar mining method. The mine produces about 600,000 tonnes per year.

Processing

After the potash ore has been crushed, screened and deslimed, the slurried ore is reagentized and pumped to a flotation circuit to separate the potash from the waste salt. Surplus brine from the closed loop process is evaporated in a vapor recompression evaporator, producing pure water, waste salt and saturated hot brine. The potash-saturated evaporator brine is combined with hot dissolver brine as a feedstock to the crystallizer circuit. White product from the crystallizer is combined with red product from flotation, centrifuged and dried in rotary dryers. The fine-grained potash product is compacted, crushed and screened to produce granular and standard sized products. The potash products are stored on-site in warehouses with a combined capacity of 150,000 tonnes.

The rock salt is conveyed to a storage bunker near the service shaft where it is crushed and screened, then hoisted to the surface and stored in one of two product warehouses. Salt is sold as de-icing agent or for other general uses. The open salt underground stopes are used to store extremely fine salt and clay waste materials and excess brine from the potash mill.

Over 95 percent of the product is shipped by rail to the company's potash terminal at the Port of Saint John for export. Potash products are stored in two storage buildings with a combined 200,000-tonne capacity. The terminal's shiploading facility can load at a rate of 3,000 tonnes per hour onto vessels that hold up to 54,000 tonnes. The remaining 5 percent of the production is shipped by truck or rail to domestic customers.

PotashCorp plans to expand its mill capacity to 1.2 Mt per year at the Sussex mine by 2015. 

Environment & Community

The Sussex mining and processing facility is a 'zero effluent' operation because of a closed loop configuration of mining, processing and waste management. That covers the mining and transporting potash and salt to the surface processing facility; processing potash; and, disposing and temporarily storing excess brine and other materials underground.