An Improved Approach to Characterize Potash-Bearing Evaporite Deposits, Evidenced in North Yorkshire, United Kingdom

S J Kemp,I Mounteney,D Wagner,C P Bell,C J B Gowing,C J Milne,F W Smith,T L Pottas

doi:10.2113/econgeo.111.3.719

Abstract

Traditionally, potash mineral deposits have been characterized using downhole geophysical logging in tandem with geochemical analysis of core samples to establish the critical potassium (% K2O) content. These techniques have been employed in a recent exploration study of the Permian evaporite succession of North Yorkshire, United Kingdom, but the characterization of these complex deposits has been led by mineralogical analysis, using quantitative X-ray diffraction (QXRD). The novel QXRD approach provides data on K content with the level of confidence needed for reliable reporting of resources and also identifies and quantifies more precisely the nature of the K-bearing minerals. Errors have also been identified when employing traditional geochemical approaches for this deposit, which would have resulted in underestimated potash grades. QXRD analysis has consistently identified polyhalite (K2Ca2Mg(SO4)4·2(H2O) in the Fordon (Evaporite) Formation and sylvite (KCl) in the Boulby Potash and Sneaton Potash members as the principal K-bearing host minerals in North Yorkshire. However, other K hosts, including kalistrontite (K2Sr(SO4)2) a first recorded occurrence in the UK, and a range of boron-bearing minerals have also been detected. Application of the QXRD-led characterization program across the evaporitic basin has helped to produce a descriptive, empirical model for the deposits, including the polyhalite-bearing Shelf and Basin seams and two, newly discovered sylvite-bearing bittern salt horizons, the Pasture Beck and Gough seams. The characterization program has enabled a polyhalite mineral inventory in excess of 2.5 billion metric tons (Bt) to be identified, suggesting that this region possesses the world’s largest known resource of polyhalite. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

Highlights

Potash is a generic term which encompasses a range of potassium-bearing minerals and industrial products, which include sylvite (KCl) and polyhalite (K2Ca2Mg(SO4)4⋅2(H2O))
Initial geologic logging of the slabbed cores (Fig. 3) and wireline geophysical logging suggested that the mineralogy of the evaporite deposits was likely to be complex
In other cases borate-group minerals were only tentatively identified as these were purely based on a single X-ray diffraction (XRD) peak

Summary

Introduction

Potash is a generic term which encompasses a range of potassium-bearing minerals and industrial products, which include sylvite (KCl) and polyhalite (K2Ca2Mg(SO4)4⋅2(H2O)). Potassium forms one of the three essential plant nutrients (the “K” in “NPK” terminology) and as a result, 95% of potash production is used as plant fertilizer. Potassium is critical for plant growth and disease resistance, and soil fertilization is necessary to replace that removed by cumulative plant uptake and soil processes. World population growth coupled with an increasing demand for protein-rich diets and a decreasing supply of arable land have driven increasing prices and high global demand for potash. The remaining 5% of global potash production is used by the chemical industry for a variety of products, including soaps and detergents, glass and ceramics, explosives, medicines, batteries, drilling muds, and electroplating (Adams and Hite, 1983; Prud’homme and Krukowski, 2006)

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