Site Name: Boulby Potash Mine - a site visit
Boulby
Redcar & Cleveland
TS13 4UZ
OS Grid Ref: NZ7618
Sub Brit site visit 26th October 2007
[Source: Paul Sowan]
THE BRIEFING
The day commenced with coffee and a first-class briefing by Neil Rowley one of the senior mine engineers, who explained what seemed like every conceivable aspect of the local mining scene in general, and the operation of Boulby mine in particular. His career history had encompassed some year working as a mining engineer in the Selby collieries complex.
| There then followed the safety briefing, specifically the use of self-rescuers for protection from carbon monoxide.It may be wondered what there is, other than in a coal mine, to catch fire underground. The answer is, of course, primarily many kilometres of heavily insulated high voltage cables. An electrical fault, setting fire to the insulation material, can result in very large volumes of very dense smoke in a surprisingly short space of time. Visibility can quickly be reduced to almost zero, and incomplete combustion can lead to the generation of exceptionally toxic gas carbon monoxide. |
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After a light lunch we all, as advised, visited the surface loos, having been warned there are none underground (but ‘there are plenty of dark corners!) We were also equipped with bottled drinking water: dehydration is a distinct possibility, as the working faces are warm – 34º C at the under-sea district we were to visit, and 45º C in the inland district. For the same reason, we stripped down completely, wearing only the very light bright orange and dayglo miners’ clothes supplied. Next we were kitted out with self-rescuers, batteries, lamps, helmets, boots, earplugs, goggles, and dust |
masks. The mining company supplied all this gear. It has an excellent safety record, and management had no intention of our party spoiling it! We were informed quite firmly well in advance not to bring our own clothing or equipment – welcome news for the two of the party who travelled up to Teesside by train. The only real formality in advance was to notify management of our boot sizes.
DOWN THE SHAFT
There are two deep shafts (each 1,100 metres) close together, and a winding-house. One shaft is primarily used for ore extraction, the other for access and supplies. The steel winding ropes (two to each cage or hopper) are inspected daily during a morning maintenance shift. The mine is ventilated by blowing fresh air down the manriding shaft, rather than extracted from the upcast shaft. It is directed around the mine by means of oiled canvas or polystyrene block brattices, and in places conducted over or under roadways by ‘air crossings.’ There is no radon, although some methane, nitrogen, hydrogen sulphide, and higher hydrocarbons are encountered in small quantities.
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The shafts are sufficiently wide to allow complete landrovers to be lowered down. About 60 of these vehicles are used in the mine (and left there when no longer serviceable.) Large machinery has to be lowered down dis-assembled, and put together in the mine.
Plummeting 1,100 metres was spectacularly smooth, in a lit but three-level crowded cage. A couple of minutes or so from the ‘off’’ we passed the balancing cage, half-way, on its way to the surface. The party travelled back over 220 million years in geological time as |
they descended through the Jurassic and the Triassic beds into the Upper Permian. It took five minutes to reach the bottom. Ore skips are wound up the other shaft at more than twice that speed.
At pit-bottom, it struck us at first as chilly and draughty as, of course, we were standing in the ventilation air intake. We found ourselves in one of two parallel roadways driven in the rock-salt bed, below the potash. This roadway, 3.6 metres from floor to ceiling and eight metres wide, is used for miners’ and others’ access to their working places. Land-rovers are used, and as we started our 11 kilometres drive to a working face we passed various underground workshops for machinery maintenance and repair, and other vehicles coming in the opposite direction from time to time. At pit-bottom we were over a kilometre down, but in one direction the route is further downhill to the lowest point about 1,350 metres below the ground.
EN ROUTE TO THE FACE
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Rock bolting - Photo by Paul Deakin C
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On the way out to the face, we stopped several times for a walkabout, and to be shewn various features. Rock-bolting is used throughout the mine, and how this was done was explained. Arrangements are made to enable persons, wearing activated self-rescuers of course, to find their way outbye in thick smoke if needs be. High-reflectance guides and directionally-tagged ropes are prominent alongside the roadway. As it is so far from pit-bottom to working faces, there are from time to time, refuge rooms with airtight doors, equipped with large numbers of air cylinders |
and smoke masks and other safety equipment. There are six of these safe havens, each large enough and with enough air to accommodate 30 persons for up to six hours. Each has a telephone.
There are four production districts – three to the north under the sea, and one inland to the south.
AT THE WORKING FACE
Still in the rock-salt bed, we examined a heading where core-sampling is done by probing ahead using a large drilling machine. By some clever manipulation, it is possible to sample above and below the bed in which the roadway is driven, as well as straight ahead.
Photo:Drilling machine for obtaining core samples
Photo by Nick Catford
Samples can be taken up to two kilometres ahead. Those who wished, collected samples (inasmuch as they could be identified) of potash, rock-salt, and anhydrite. The anhydrite, being a dull grey colour, was easy to identify. But we were advised that the best way to tell the difference between potash and rock-salt is by taste, as both materials occur is a variety of colours due to impurities such as clays and iron minerals. Both pure sodium chloride and pure potassium chloride are of course plain white/colourless crystalline materials. But neither the rock-salt beds nor the potash beds are 100% one compound or the other, and each can occur as clear, white, grey, amber, brown, pink or red material. Those wishing to sample the taste of potash need do no more than invest in some ‘low-sodium’ table salt (potassium chloride) which tastes salty but not quite the same.
We were warned that sylvinite is hygroscopic and our samples would soon crumble if not kept dry at home.
| There being no rock-cutting in progress at the time (work was in hand on a maintenance question) we then went to admire the machinery used. This mine is not worked by drilling and blasting, but uses very large machines with boom-mounted cylindrical cutting heads of the order of a metre diameter, and several metres wide, well-armed with tungsten carbide-tipped cutting teeth. The device has an integral collecting scoop which conveys the cut ore to the rear, where is it delivered to a most ingenious local conveyor system. These |
Remotely controlled rock cuting machine
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mobile, flexible local conveyors (looking like huge long centipedes without all the legs) can be twisted and turned to snake around corners and so serve any scene of operations without the need for a flock of dumper-trucks, such as generally found in gypsum mines, although some shuttle cars are used.
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Photo:Conveyor
Photo by Paul Deakin
The mobile conveyors are up to 65 metres long, which I think can be shortened or lengthened as required by adding or removing sections. They convey material to the main conveyors, and thus to the winding-shaft.
Click here forfurther information and pictures of Boulby Mine
[Source: Paul Sowan]
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