The final rock formation at Winsford has four distinct rock salt seams or ‘halite’ as it is known (halite is taken from the Greek word ‘hals’, meaning salt). Each rock salt seam averages 25 metres (80ft) in thickness.

The remaining strata consist of rock salt with Keuper Marl bands and Keuper Marl. The youngest of the Triassic rocks in the series, Keuper Marl is usually amber or brown in colour, although on occasions it can be blue or green. Due to many of the influencing geological aspects, the colour of Winsford’s salt varies greatly – it can range from clear to pink through to dark brown, although a mixture of dark brown and pink is most commonly found.

The beds of salt worked at Winsford are relatively flat (see diagram). There are two economically workable beds of salt known locally as Zone ‘B’ and Zone’F’. These beds lie between 130 and 220 metres below the surface. As discussed earlier the bed is, on average, 25 metres thick but the purest salt is located in the lower part of the bed.

The Winsford Mine was the first Compass Minerals production facility to purchase a continuous mining machine to replace the traditional drill-and-blast method of salt extraction. The continuous mining process uses a machine to cut rock away from the mine face. It’s simpler, takes less mining equipment, less underground transportation machinery and less manpower than the drill-and-blast process that it replaces, and reduces fuel use and emissions.

Once the rock salt has left the working face it is carried on the conveyor system to the underground crushing and screening plant. To avoid any waste metal entering the crushing plant, the rock salt is conveyed under metal detectors and magnets at three different points. A series of crushers and screens then reduce the size of the salt and separate it into 0-6mm and 0-10mm product.

The crushing plant and all the conveyors are automated and controlled from No 5 Shaft surface, where a controller monitors underground activity via television screens and passes any requests via radio.

The finished product leaves the crushing and screening plant via a conveyor leading to No 5 Shaft, from where it is elevated to the surface in 9-tonne bottom dump skips. Once the skip reaches No5 Shaft surface it discharges onto a conveyor which takes the salt to surface. En route, it is sprayed with a small dosage of a basic anti-caking agent, a treatment that enables rock salt to flow f ........