The Sirius Minerals North Yorkshire Polyhalite Project
Tristan Pottas, was unable to give this talk but two of his colleagues gave an interesting overview of this exciting new mining project near Whitby. Asher Haynes described the process of exploration and the excitement of discovering a truly vast deposit of polyhalite in North Yorkshire. Polyhalite is an unusual multi-nutrient mineral that is an exceptionally good fertilizer as it is essentially chloride free, does not affect the pH of the groundwater when applied, and needs virtually no processing. However this valuable resource lies 1500m below the National Park with all its tight planning restrictions. Nevertheless the project would bring significant economic benefits to the area by way of employment and would contribute to the national economy. Sirius had been given planning consent after describing these advantages and developing an extraction method which placed most of the infrastructure below ground level. The Company are currently seeking the necessary finance in readiness to commence construction.
David Warburton, completed the evening by describing the characteristics of polyhalite (K 2 MgCa 2 (SO 4 ) 4 2H 2 O) and his recent research Masters degree at University of Leeds where he had attempted to discover how this mineral is formed. This deposit is most unusual in its thickness, averaging 25m, whereas deposits of around a metre are the norm. Polyhalite is a late stage mineral to form in a sequence of evaporates, so how does such a huge volume occur? David attacked the problem from a geochemical perspective, looking at the isotopes of the various elements which all pointed to formation from seawater during Permian time. The study of thin sections by the BGS suggested that polyhalite replaced anhydrite and other minerals, very soon after the original crystals had formed. The results support the formation of polyhalite via seawater concentration processes, though the topic is far from closed and much more research could be completed.
The combination of a more sustainable approach to the extraction of a valuable resource and the attempts to discover its formation and the questions raised made for a fascinating evening. The speakers were both enthusiastic and hopefully will return in due course to update us on their progress.
