Summary:
Potash at the Milestone Project area occurs conformably within Middle Devonian-age sedimentary rocks, and is found in total thicknesses ranging from approximately 30 to 40 m at a depth of approximately 1,350 to 1,450 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.
In the KLSA 008 Lease area, the Esterhazy, Belle Plaine, and Patience Lake Members are present. Also present is the “White Bear Marker Beds,” which is a distinctive unit of thin interbedded clay, halite, and sylvinite beds between the Belle Plaine and Esterhazy Members but is of insufficient thickness and grade to be attractive for mining.
The typical sylvinite interval within the Prairie Evaporite Formation consists of a mass of interlocked sylvite crystals that range from pink to translucent, and which may be rimmed by greenish-grey clay or bright-red iron insolubles, with minor halite randomly disseminated throughout the interval. Local large (greater than 2.0–2.5 centimeters [cm]) cubic translucent to cloudy halite crystals may be present within the sylvite groundmass, and overall, the sylvinite ranges from a dusky brownish-red color (lower grade, 23%–27% K2O grade with an increase in the amount of insolubles) to a bright, almost translucent pinkish-orange color (high grade, 30%+ K2O grade). The intervening barren beds typically consist of brownish-red, vitreous to translucent halite with minor sylvite and increased insolubles content.
The potash mineralization identified from drillhole data consists of three principal members:
Patience Lake Member:
Historically the Patience Lake Member in the Regina area was noted as having 9 potash beds and 10 clay seams, with 3 potash beds at the top having been eroded and their corresponding clay seams compressed into a clay zone at the top of the Member (Phillips, 1982). Identifying the individual clay seams and potash beds consistently between drill holes can be problematic, therefore the approach of defining sub-members that occur between well-defined clay seams and, more importantly, with similar mineralization between different wells. This is particularly important for selective solution mining, where differences in grade can result in different cavern growth potential.
For KLSA 008, the Patience Lake Member was divided into 4 sub-members, named Patience Lake A through D, with A being the lowest sub-member. The A member ranges in thickness from 4.15 m to 6.00 m, and K2O grade from 10.39% to 16.04%. Note that these, as well as the numbers below, exclude the results from Milestone-002, which experienced a general dissolution event.
The B Member ranges from 1.80 m to 6.68 m in thickness, and K2O grade from 16.26% to 26.66%. The C Member ranges from absent to 4.05 m in thickness, and K2O grade from 8.09% to 27.35%. The D Member is much lower grade and fell well below cut-off grade (15% K2O) across the Lease, with grades ranging from 2.91% to 11.65%, and thicknesses from absent to 4.65 m.
Belle Plaine Member:
Historically the Belle Plaine Member in the Regina area was noted as having all 9 potash beds and 7 clay seams, although the latter was described as somewhat indistinct (Phillips, 1982).
Following the same methodology as with the Patience Lake Member, the Belle Plaine Member was divided into 3 sub-members, A through C. The A member ranges in thickness from 0.9 m to 2.58 m, and K2O grade from 2.89% to 34.53%., while the B member ranges in thickness from 1.2 m to 1.95 m, and K2O grade from 9.81% to 19.9%. The C member ranges from absent to 3.86 m in thickness, and from 14.9 % to 37.77% in K2O grade.
Esterhazy Member:
Historically the Esterhazy Member in the Regina area was noted as having 5 potash beds and 4 clay seams, although the latter was described as poorly defined (Phillips, 1982).
Following the same methodology as with the other 2 Members, the Esterhazy was divided into 3 sub- members, A through C. The A member ranges in thickness from 1.80 m to 6.81m, and K2O grade from 3.42% to 7.61%, while the B member ranges in thickness from 1.70 m to 4.80 m, and K2O grade from 7.3% to 18.45%. The C member ranges from 2.40 m to 6.68 m in thickness, and from 7.14% to 32.40% in K2O grade.
Other Sylvite mineralization also occurs in the White Bear Marker Beds, which are found between the Belle Plaine and Esterhazy Members. However, based on the geophysical logs and assays for the eleven exploration wells and three production wells drilled for WPC, these beds are of insufficient thickness (typically 1 to 3 m) and grade to be economically mineable on KLSA 008.
Carnallite
Carnallite is present to a limited degree in all potash members of the Prairie Evaporite Formation; no significant concentrations of carnallite have been detected in the Patience Lake or Belle Plaine Members in KLSA 008. However, drilling by WPC has confirmed that only portions of the Esterhazy Member on the KLSA 008 Lease area contain carnallite above 6%. This differs from the expectations of Holter (1969) and Fuzesy (1982), who have shown elevated carnallite concentrations in the Esterhazy Member within the entire KLSA 008 Lease area. Carnallite is also present as a separate unit, 6 to 10 m below the Esterhazy Member in exploration wells M 004 and M 005 and in production wells W 001-2, W 002-2, and W 003-2.
For purposes of estimating the mineral resource on the KLSA 008 property, the Patience Lake, Belle Plaine, and Esterhazy Members are considered to have solution mining potential. Solution mining of the high-carnallite portions of the Esterhazy Member in the vicinity of wells M 001, M 002A, M 003, M 009, and W 001-2 may be possible if the resulting brine can be blended with brines from other potash members in other caverns. Consequently, the high-carnallite areas of the Esterhazy Member were included in the resource estimates. The White Bear Marker Beds are not considered to have solution mining potential because of their minimal thickness and low grade.