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The Probus Club of Stokesley and District Stokesley Town Hall on Tuesday 21st April 2015

Speaker – Peter Woods – York Potash at Dove’s Nest

Peter Woods, a retired geologist, was born in East Africa and worked for De Beers in Nigeria. He now works as a consultant to Sirius Minerals, the company proposing to develop the York Potash mine. He came to Britain during the Biafran war and expected the next project to be in South America. Instead he worked on the development of the Boulby Potash mine.  

He gave an excellent description of the plans for the new mine and answered many questions from Members on all aspects of this major project.
Peter noted that Boulby was the deepest mine in Europe when it was developed and must be considered a success as it is still going strong after 40 years. He explained that the new project is different in many ways. He gave an outline of the proposals and allowed plenty of time for questions.
Unlike many mine developments, there will be very little to see at ground level. The low buildings constructed at the top of a hill will be effectively screened with trees. One of the current questions to be resolved is the disposal of the spoil from the shafts and the tunnel.

Previous ironstone mining tips were all used over time by developers. It is hoped that the material from the shafts can be spread on farmland after stripping the topsoil. The topsoil would then be relaid on top.
The main issue to date has been obtaining Planning Permission in the National Park. The National Park Authority has hired an external consultant to advise them and this has proved to be both expensive and slow.

The new mine will be 1500m deep and the shafts will pass through water-bearing sandstone. Water can pose a serious problem during construction. At Boulby, one shaft used ground reezing to control it during sinking and the other used chemical grouting. The latter worked well but the ground freezing was not completely effective. The gap in the ice wall resulted in the shaft flooding. This led to a delay of 18 months in the completion of this shaft.

The remainder of Peter’s talk was responses to the many questions from Members. The initial production is planned to be 5 million tonnes per annum. The attraction of polyhalite is that it is much less soluble than muriate of potash, the most common form of potassium fertiliser. This is predominantly potassium chloride and heavy rain can dissolve the fertiliser very quickly. Polyhalite is mainly potassium sulphate which will not be washed away so easily and therefore will last much longer.

The York Potash deposit is the largest in the world. It is planned that the water will be controlled during sinking of the shafts by chemical grouting, but contractors for both methods are interested. A 1300m shaft has been uccessfully constructed in China recently using ground freezing. The chemical grout is now much better than the material used at Boulby and there is no evidence that it is harmful to health.

The mined polyhalite will be transported by conveyor through a tunnel to Wilton. A service railway and ventilation ducts will also run through the tunnel and electricity cables will be laid elow the conveyor. The tunnel will be constructed in the Redcar mudstones which are at ground level at Wilton but which dip well below the old ironstone mines. This is important to avoid the risk of the tunnel being flooded with water which has accumulated in the abandoned mine workings. 3 ventilation shafts are proposed at Egton, Lockwood Beck and near Tocketts Mill. Power may be supplied from the Dogger Bank offshore wind farm.
Polyhalite is an evaporite material and was discovered in 1938 during drilling for oil and gas. The depth to the deposit has been one of the main reasons why it has not been mined until now. The bed is continuous from Whitby to Scarborough but gets deeper as it goes south. The thickness of the seam varies from 10m to 40m. No fracking will be used because of the great depth of the bed.

Planning Approval is close for the tunnel but for the mine, it is still some time away. A so called Section 106 Agreement is still under discussion. This is likely to include 9 million trees, new rolling stock for the Whitby railway and the employment of apprentices. Land acquisition matters are largely resolved.
It is hoped to deliver the first product to Wilton in 3-4 years. A new Application for Planning
Approval will be submitted in the near future.

There will be very little processing of the material apart from crushing. Making a slurry would have caused disturbance at the surface and would have necessitated additional processing at Wilton. Few jobs will be created at the port, but for the 3 shifts needed for 24 hour working, about 1000 jobs will be created at the mine. Its life is estimated to be about 100 years. The ventilation fans will also be below ground.
The first customers are likely to be the Chinese and South Americans. There will be 3 main products – sulphates of potassium, calcium and magnesium. Until now the market has been small because of a lack of supply. The anticipated market is huge.

Subsidence will not be a problem, because about 50% of the material will not be dug. Receipt of Planning Permission will make the task of raising money easier. It is estimated that establishing the mine and associated infrastructure will cost about £1billion.

The route of the 8m tunnel and its depth have been published. The tunnel will not require lining for most of its length. The tunnel is not a cheap solution, but a major upgrading of the existing railway would be required if this were to be used and the noise generated by the heavy trains would not be acceptable.

York Potash