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Potash – recent exploration developments in North Yorkshire.
... Polyhalite, ideally K 2 Ca 2 Mg(SO 4 ) 4 ·2H 2 O, is an otherwise rare mineral that occurs in substantial quantities in a deeper evaporite bed. A new mine is currently being developed to exploit the polyhalite deposit in North Yorkshire, and interesting assemblages of borate minerals have been identified in the drill cores (Dearlove et al. 2013). An exploration target of 6.8-9.5 billion tons has been identified (Dearlove et al. 2013). ...
... A new mine is currently being developed to exploit the polyhalite deposit in North Yorkshire, and interesting assemblages of borate minerals have been identified in the drill cores (Dearlove et al. 2013). An exploration target of 6.8-9.5 billion tons has been identified (Dearlove et al. 2013). ...
... In the Canadian marine evaporite deposits of Newfoundland, Nova Scotia, and New Brunswick, howlite is the principal borate mineral (Smith and Medrano 1996). Recent discoveries of howlite and danburite in exploratory boreholes drilled by York Potash to test a polyhalite deposit to the south of Boulby mine (Dearlove et al. 2013) suggest that the English Zechstein is mineralogically more diverse than previously thought and worthy of further detailed study. The Canadian assemblage was originally interpreted in terms of a volcanic borate-rich fluid input (Roulston and Waugh 1981), but boron isotope studies are consistent with a simple seawater source without any need to invoke a more exotic explanation (Grice, Gault, and van Velthuizen 2005). ...
Volkovskite is reported from the Late Permian Boulby Halite Formation at Boulby mine on the northeast coast of England. It was first found in late 2009 as colourless to white highly reflective cleavage fragments in insoluble residues concentrated in filters at the mine’s processing plant. These were traced to Panel 845 North 4, about 9 kilometers north of the shaft bottom, where volkovskite was found in situ as rosettiform platy aggregates. Further occurrences were subsequently identified in two exploratory boreholes, and in Panels 848 and 887, in the Dirty Secondary Ore unit of the Boulby Potash in the northern part of the mine. Individual bladed crystals reach 7 cm in length and occur as large aggregates exceptionally reaching 20 cm across. This is the first record of volkovskite in the British Isles and appears to be the first report of the mineral from the marine evaporites of the Zechstein basin.
... Polyhalite, which may serve as a suitable fertilizer to supply four nutrients, is less water soluble than the more conventional sources and may conceivably provide a slower release of nutrients (Barbarick, 1991). It can also be used directly as a long-release fertiliser (Smith et al., 2014). The slow-release nature of polyhalite has the potential to improve K use efficiency (KUE) as it prevents leaching and provides prolonged nutrient release. ...
... The location of the boreholes is shown in Figure 2. This borehole core material covers the Zechstein Group cycles EZ2-5 of the classic carbonateevaporite structure (Smith 1989;Peryt et al. 2010;Smith et al. 2014) and sequence stratigraphic cycles ZS3-7 of the alternative evaporite-carbonate organization (Tucker 1991) throughout the Yorkshire Sub-basin (Smith 1989). The stratigraphic range of the boreholes is shown in Figure 3 and Table 1). ...
Evaporites characterize the Lopingian of Europe but present obstacles for biostratigraphic analysis. Here we present a case study for processing the Lopingian Zechstein Group evaporites of central-western Europe for the recovery of palynomorph assemblages. We demonstrate that full recovery is easily achieved with two main modes of palynomorph preservation observed; palynomorphs are either exceptionally well-preserved and orange-brown in colour, or poorly-preserved, brown-black, opaque and fragmented. The latter are reminiscent of palynomorphs of high thermal maturity. However, we propose that the intact nature of preservation is a result of the rapid growth of near-surface halite crystals, with their darkening a consequence of locally-enhanced heat flux due to the relatively high thermal conductivity of salt. This case study has enabled novel insight into an otherwise undescribed environment, and demonstrates the utility and possibility of extracting palynomorphs from a variety of rock salt types. This method should be applicable to a wide range of ancient evaporite and could also be applied to other Permian evaporite systems, which are used as analogues for extra-terrestrial environments.
The rare mineral kalistrontite, K2Sr(SO4)2, has been discovered in exceptional quantities in exploration boreholes targeting Permian polyhalite [K2Ca2Mg(SO4)4·2(H2O)]-bearing evaporite deposits in North Yorkshire, U.K. The kalistrontite is associated with anhydrite, polyhalite, halite, magnesite, and traces of celestine in the Fordon (Evaporite) Formation, English Zechstein 2 cycle, at depths of ∼1.5 to 1.7 km below surface. It was first encountered here during quantitative X-ray diffraction assays of composited drill-core samples over an identified ∼50 m interval in York Potash Ltd.'s boreholes SM6, SM9, and deflections SM9A and 9B. X-ray diffraction including structural refinement, thermal analysis, Raman spectroscopy, petrographic examination, quantitative microanalysis, and Sr isotopic analysis have been employed to fully characterize the kalistrontite and determine its genesis to understand its distribution and significance for the polyhalite deposits. Petrographic examination reveals that the kalistrontite is present in two general forms. First as irregularly shaped, poikilotopic millimeter-scale patches of subhedral, equant to elongate millimeter-scale crystals that enclose fine, rounded, irregular anhedral and rarely euhedral crystals of anhydrite, halite, and magnesite. Second as a vein-fill formed of an interlocking mosaic of elongate sub-millimeter scale, euhedral crystals that are compositionally zoned and again enclose fine rounded anhydrite and halite crystals at vein margins. Kalistrontite displays largely replacive contact relationships with both the earlier and generally simultaneously formed anhydrite and halite but before at least some of the polyhalite. Vein-fill kalistrontite was deposited by mineralizing fluids proceeding along fractures, patchily replacing the pre-existing low-porosity anhydrite and halite. EDX microanalysis of the North Yorkshire kalistrontite indicates a purer composition than previously reported but some (5-12% stoichiometric) substitution of Ca for Sr is identified and directly linked to petrographic textures identified during backscattered scanning electron imaging. Improved resolution XRD data for the kalistrontite is comparable to that previously published, with similar unit-cell dimensions [a = 5.45826(5) Å, c = 20.8118(2) Å, α = 90°, β = 90°, γ = 120°, V = 536.968(3) ų] and space group R3m (166), despite the limited Ca substitution for Sr. Thermal behavior, published for the first time, shows that kalistrontite is essentially stable from ambient to ∼960 °C. Melting occurs from ∼960 to 1430 °C with a resulting weight loss of 62.57%, accompanied by the evolution of SO2. Minor endothermic features are tentatively ascribed to the boiling of K from surface sites. The first published Raman spectrum for kalistrontite shows a major frequency shift at 968 cm⁻¹ with minor features of decreasing intensity at 458, 617, 1095, 1152, 650, 170, and 127 cm⁻¹. Consistent ⁸⁷Sr/⁸⁶Sr values for kalistrontite and anhydrite (mean, 0.707014 ± 0.000010, 2 S.E. and 0.707033 ± 0.000020, 2 S.E., respectively) along with very similar values obtained for the polyhalite are indicative of Late Permian seawater in an open environment with very limited evidence of basin constriction or Sr contribution from hydrothermal or meteoric source(s). When compared to the LOWESS global curve, the ⁸⁷Sr/⁸⁶Sr values suggest a consistent formation date of 255 ± 2 Ma (late Wuchiapingian), the first published date for the EZ2 deposits in North Yorkshire. Diagenetic processes, particularly the late-stage supply of K- and Sr-rich fluid, must have proceeded extensively in the North Yorkshire deposits. However these show only limited spatial development, within the shelf zone on the margins of the main polyhalite deposit. The K-rich nature (26.3 wt% K2O) of kalistrontite, compared to other K-bearing evaporite minerals (e.g., kainite 18.9 wt% K2O, carnallite 17.0 wt% K2O, polyhalite 15.6 wt% K2O), has a significant effect on borehole γ-ray response (303 compared to 229, 200, and 185 API units, respectively) and therefore considerable implications for evaporite deposit modeling and the determination of deposit-grade. Understanding the character and distribution of kalistrontite is necessary for modeling the nature, extent, and grade of the world's richest-known deposit of polyhalite. York Potash Ltd. has recently commenced construction of the $3.0 bn Woodsmith Mine to support large-scale polyhalite production, promising the creation of thousands of jobs and a boost to both local and national economies. First production is scheduled for late 2021.
It is contended that the Zechstein Sea was formed when the N rim of a chain of interlinked sub-sea level inland drainage basins was breached or overridden by a relative rise of ocean level. The rim remained as a barrier near ocean level and exerted a strong influence on the subsequent depositional history of the whole basin. Rates of sedimentation in the basin increased when halite was formed and, despite continuing subsidence, the original basin gradually filled. Rocks of the English sub-basin comprise 4 main cyclic carbonate-evaporite sequences which interdigitate marginally with semi-continental red beds; a number of sub-cycles are also recognised.-from Author
Some years ago a few small grains of an unknown mineral were separated by F. H. Stewart from well cuttings from the Permian lower evaporite bed of the Eskdale no. 2 borehole, sunk by the D'Arcy Exploration Company near Aislaby, north Yorkshire. The mineral (not then identified) was mentioned in an account of the mineralogy of this evaporite bed (Stewart, 1949, p. 626). Flame tests suggested that boron and strontium were present, and this was confirmed by Dr. R. L. Mitchell of the Macaulay Institute for Soil Research in Aberdeen, who, by spectrographic work, found that these were the main constituents, and that very much smaller quantities of Ca, Mg, Ba, Na, and K were present.
In the Fordon No. 1 borehole, sunk by the D’Arcy Exploration Company to a depth of 7559 feet near Scarborough, the Permian succession contains 1387 feet of evaporites. This paper describes and discusses the Lower Evaporites in detail. These are 1069 feet in thickness, and the petrography of each of the main ten subzones they contain is described. The major constituents are dolomite, anhydrite, polyhalite, kieserite and halite. Minor constituents include magnesite, glauberite, celestine, aphthitalite, pyrite, sulphoborite, sulphur and talc. Glauberite and sulphoborite are new to Britain.
The origin of the rocks is discussed in relation to experimental work on salt systems. The ten subzones can be placed in three cycles of sedimentation, each ended by a relatively sudden increase in rate of subsidence, the middle cycle consisting of two sub-cycles. The upper and lower cycles are relatively simple, consisting mainly of halite and anhydrite, but the middle cycle is more complex, and contains rocks unlike any so far recorded from this country. On textural evidence it is concluded that, whereas gypsum was a primary mineral of the upper and lower cycles, the calcium sulphate of the middle cycle was deposited as anhydrite. The latter has been replaced by polyhalite on a large scale, and it is believed that this change was penecontemporaneous, and released enough calcium for the formation of a large amount of primary polyhalite. The later succession has therefore been considerably modified, and some of the polyhalite and kieserite-bearing subzones may represent the potash-free magnesium sulphate and kainite zones of the experimental succession.
There is evidence of a considerable number of replacements. Most of the major ones are probably penecontemporaneous. Others are post-consolidation effects, probably due to rise of temperature and pressure during burial. Some, like those involving glauberite, have probably been effected by solutions rising from a lower cycle; others have been effected by downward or sideways moving solutions from the same or a higher cycle. Some replacements are later than movement and recrystallization of halite under pressure.
A count of rhythmic layers in the middle cycle gives information on rates of deposition and suggests that this cycle may have been deposited in about 25000 years.
The Fordon Lower Evaporite succession is compared with that in other parts of Yorkshire. The Fordon evidence favours Lotze’s correlation of the Lower Evaporites of Yorkshire with the Middle Zechstein of Germany.
Revised names of some Upper Permian strata in eastern England are proposed and defined, together with new names for some strata previously without formal names; the new and revised names are based on nominated type localities and are intended to replace existing names that were confusing or inappropriate. We propose that the names Lower and Upper Magnesian Limestone in the Yorkshire Province be replaced by the new names Cadeby (Magnesian Limestone) Formation and Brotherton (Magnesian Limestone) Formation respectively and that the Lower and Middle Magnesian Limestone in the Durham Province should become the Raisby (Magnesian Limestone) and Ford (Magnesian Limestone) formations respectively. The Middle Marls are renamed the Edlington Formation in both provinces and the new names Sherburn (Anhydrite) Formation, Sneaton (Halite) Formation and Littlebeck (Anhydrite) Formation are proposed for the Upper Anhydrite, Upper Halite and Top Anhydrite formations. The term Roxby Formation is proposed to replace the present name Upper (or Saliferous) Marls.
Zechstein and Fordon Evaporites of the Atwick No. 1 borehole, surrounding area of NE England and the adjacent southern North Sea
- V S Colter
- G E Reed
Colter, V. S. and Reed, G. E. 1980. Zechstein and Fordon Evaporites of
the Atwick No. 1 borehole, surrounding area of NE England and the
adjacent southern North Sea. Contributions to Sedimentology, 9,
p. 115 -129.
Iron-boracite from the English Zechstein
- J K Milne
- M J Saunders
- P J E Woods
Milne, J. K., Saunders, M. J. and Woods, P. J. E. 1977. Iron-boracite from
the English Zechstein. Mineralogical Magazine., 41, p. 401 -406.