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. Winsford rock salt is more than 90% pure sodium chloride, with the remaining insolubles consisting mainly of Keuper Marl, which is a layer of clay from the late Triassic or ‘Keuper’ period. Keuper Marl has weathering properties, which give Winsford rock salt its unique ‘thatching’ effect, protecting the salt quality. Marl also contributes to improved friction when salt is used as a highway deicer.

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.

- subscription is required.