Summary:
Deposit Type
Potash at the Esterhazy Potash Facility area occurs conformably within Middle Devonian-age sedimentary rocks and is found in total thicknesses ranging from approximately 100 to 131 ft. (30 to 40 m) at a depth of approximately 3,280 to 3,855 ft. (1,000 to 1,175 m). Evaporites are generally formed by seawater flowing into landlocked basins, followed by the evaporation of the seawater and precipitation of the dissolved salts. Progressive solar distillation of these salt-rich brines results in sequentially precipitated beds of limestone (CaCO3), dolomite (CaCO3·MgCO3), anhydrite (CaSO4), halite (NaCl), carnallite (KCl·MgCl2·6H2O), sylvite (KCl), kieserite (MgSO4·H2O) and other calcium and magnesium salts.
Property Geology
The Esterhazy Potash Facility is situated in the eastern extent of what is commonly termed the “Commercial Potash Mining Belt,” where potash is mined by conventional underground methods. The total thickness of potash beds in the Prairie Evaporite at Esterhazy ranges from approximately 100 to 131 ft. (30 to 40 m) at a depth of approximately 3,100 to 3,800 ft. (950 to 1,150 m).
In the Esterhazy area, the Esterhazy and White Bear Marker Beds are present. The White Bear Marker Beds, a distinctive unit of thin interbedded clay, halite, and sylvinite horizons between the Belle Plaine and Esterhazy Members, is insufficient in thickness and grade to be attractive for mining.
The potash mineralization in the Esterhazy Member includes five major potash-bearing beds that are extracted by conventional mining machines. The key mining horizons are initially delineated using information gathered during production drilling, using geophysical logging technology. These logs are compared to physical core to evaluate the quality of the mineralization.
Esterhazy Potash Deposit
The potash mined at Esterhazy is a mixture of halite and sylvite and in some parts of the mining area, moderate amounts of carnallite. The key mining horizons are initially delineated using information gathered during exploration drilling using geophysical logging technology. These logs are compared to physical core to evaluate the quality of the mineralization.
The potash deposit is generally uniform and laterally continuous. The grade is estimated using geochemical assays of core or chip samples. Properly calibrated, the gamma response from well log data can be converted to indicate the amount of potash in the formation as a %K2O. Gamma Ray Equivalent Calculation (GREC) can be applied to interpret and verify the quality of the ore where core may not be available. The neutron-density log is used to indicate the presence of carnallite. Confidence in this correlation is gained by comparing GREC to assay results.
Deposit Dimensions
In the Esterhazy area the potash mineralization is from the Esterhazy Member. It includes five major potash-bearing beds that are extracted by conventional mining machines. The naming convention at site refers to the beds in the Esterhazy Member as beds 50, 45, 40, 35 and 30 (in ascending order). The highest-grade potash is hosted in Bed 40. It has an average thickness of 4.3 ft (1.3 m). It is possible to encounter variation in the thickness and grade of these beds, but usually the normal stratigraphy is present.
Mineralization
Potash mineralization contains sylvinite, a mixture of the iron oxide-stained halite, sylvite and carnallite. Minor amounts of insoluble minerals are also present, most notably in the 45 Bed. When present interstitially or as more massive pods, carnallite can deteriorate rapidly or be preferentially dissolved. The color of the potash can vary from light orange to deep red-rimmed crystals. The mineralization can be locally bedded or massive. The halite and sylvite crystals can range from small to more typically coarse to large. This can be attributed to the conditions during deposition as there has been no alteration.