Site Records

Site Name: Boulby Potash Mine - a site visit

Boulby
Redcar & Cleveland
TS13 4UZ
OS Grid Ref: NZ7618

Sub Brit site visit 26th October 2007

INTO THE POTASH BED
All the permanent roadways are driven in the rock-salt bed, as this material is mechanically strong enough (when rock-bolted) to afford good permanent tunnels.  Thus it is that the enterprise has to mine low-value rock-salt, before it can reach the more valuable potash.  Potash is mined five days a week, and rock-salt (to extend the roadways) the other two days, Fridays and Saturdays.

Each district has a 'bait table' which acts as a meeting point and an area to take a break - Poto Paul Deakin  C

It was now time to drive up one of the numerous internal inclines to reach a ‘panel’ being worked in the potash beds lying above the access roadway ceilings.  Around 10 – 12 metres thickness of rock separates the access roadway ceiling from the mine panel floor above.  As the potash is a mechanically weaker material, the cavities left by mining it are, when mined-out, left to fall in, which they tend to do within six months or so.  The mined-out panels ultimately close up by floor-heave (about one metre in three months), pillar failure and ceiling collapse. Here, similar mining equipment is used and the main new point of interest was the

The potash-yielding bed has a thickness of about seven metres, but the mined cavities 3.6 metres high are designed to leave two metres of raw potash to form a ceiling.  Above this is marl, which would not form a sufficiently secure ceiling.

The mined panels are 55 metres wide, three or four parallel roadways being driven forward with two lines of oblique un-mined rock pillars arranged en echelon left between them.  Each panel is of the order of 600 metres long.  About 3,000 tonnes of ore a day (an advance of 10 metres per machine per shift) can be mined form each panel.

It was certainly warm at the innermost end of the mine – much like a crowded London tube train, but more acceptable in that the air here is much drier (and not so smelly!)

BACK TO THE SURFACE
Before getting back into the cage to get back to ground level, we toured the pumping plant.  Most of the mine is extremely dry, but saturated brine (containing both sodium and potassium chlorides) is pumped to the surface from sumps at the lowest points, at a rate of 1,000 gallons per minute, and used in the processing plant.

Sadly, there was not time to visit the Dark Matter Laboratory near pit-bottom.

On emerging at the surface, we went to see the enormous electrical winding engine, the steel cable, and the men upon whom our lives in an 1,100 metre deep hole had depended.  It is all controlled from comfy chairs in a cabin well-supplied with computer screens full of data from instrumented gadgets in and around the shafts.  Then we watched enormous skips holding 45 tonnes of material each being discharged into hoppers feeding the processing plant.  There was about a minute or a minute and a half between skips arriving at ground level, so they are clearly hoisted up the shaft more than rapidly!

Then back to the changing rooms for more than welcome showers, a photographic perambulation around some of the surface buildings.

The winders for the two shafts are in two adjacent halls with a central control room overlooking both of them. When first installrd, the winder on the 'rock shaft' was the largest winder in the northern hemisphere. From the winding hall we walked the short distance to the rock shaft where we saw the skips discharge their rock salt (as it was a Friday) into the hoppers. The rock shaft winds at a much higher speed than the man riding shaft taking just two minutes to bring the rock to the surface. This is an automatic process and is only stopped for essential maintenance.

After a vote of thanks to our guide who had given up most of a day for us (about 10.30 to almost 16.00) we made our preparations for going home.

Click here forfurther information and pictures of Boulby Mine

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