Sent to the Salt Mines
Following on from several recent underground expeditions to the Alderley Edge copper mines and North Wales lead/zinc mines, several intrepid members of the Chester office decided to go for the big (or should that be deep) one!
Boulby mine is on the Cleveland coast and is Europe’s second deepest mine at 1200m below ground level. Paul Hayes managed to arrange a trip down the mine for a small party of Chester office engineers (John Booth, Keith Nicholls, Stuart McCrae), and guests (Sam Fishburne, Dave Cage and Geoff Booth).
The day started with a presentation from Neil Rowley – Health and Safety Manager (Cleveland Potash) on the history of the mine, local geology, and mining operations. Following a safety briefing, the team was kitted out in fetching hi-vis yellow/orange kit, and several of the less self conscious preferred shorts rather than overalls. The temperature at the working face gets up to around 40˚C so this turned out to be a good choice!
Then it was off to the man riding cage at one of the two main shafts. Once in the shaft the cage takes about 6 minutes to descend to pit bottom. Around the shaft bottom there are stores and work shop areas. All the equipment and spares has to be brought down the shafts in sections, so vehicles and mining equipment are built and maintained in these workshops by a team of fitters and electricians. Transportation underground is by transit van or land rover, each vehicle stripped out to reduce weight and fire risk, and each vehicle with a team of miners, drillers, or visitors crammed in, looking like something from hi-vis Mad Max.
Neil Rowley then took the team about 7km out under the North Sea along the main mine haulage route. Most of the access tunnels are mined in the lower halite (rock salt) beds because these rocks are more stable than the overlying potash beds. At the current working face, an access ramp takes the haulage route into the potash beds, where a team of miners operates a rotating face cutter, loads the potash onto dump trucks which load the ore through a primary crusher and onto conveyors for transport to the shaft and then to the surface. At current market rates the potash is ten to fifteen times more valuable than the halite from the lower strata, so potash is mined at two faces five days a week, and salt from one face at weekends.
The geology and rock mechanics of the potash and halite beds is key to the economic viability of the mine. Horizontal exploration holes are drilled in prospective new areas of mining. Drilling commences in the halite and then the holes are angled upwards into the potash. A gamma ray probe then tests the quality of the potash, anything over 30% pure is considered viable, so most future planning of mining operations relies heavily on the geologist’s predictions. The drill hole seen by the Geotechnics team was about 250m in, but the core logging looked pretty easy – salt all the way!
Having seen the drilling, mining and roof bolting operations at the working face, it was back to the shaft and to the surface for a shower and a refreshing cup of tea. Many thanks to Neil Rowley and his colleagues at Cleveland Potash for their generous hospitality.