Economic geology of southern Saskatchewan potash mines

Ore Geology Reviews 113 (2019) 103117

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Economic geology of southern Saskatchewan potash mines

T

Paul L. Broughton Broughton and Associates, Calgary, Alberta, Canada

A R T I C LE I N FO

A B S T R A C T

Keywords: Potash Prairie Evaporite Sylvite Carnallite Halite Salt dissolution

Canadian commercial potash deposits are located in the southern Saskatchewan area of a Middle Devonian evaporite basin that extends across western Canada and into adjacent areas of northeastern Montana and western North Dakota. There are eleven mines in Saskatchewan that annually produce approximately 23 Mt of KCl from halite-sylvite ore associated with the 60 m thick upper interval of the Prairie Evaporite Formation. Of these, eight mines are conventional underground operations at 900–1100 m depths. Solution mining is used at three sites where the ore is buried to 1500 m depth or where this methodology was a necessary remedial action responding to flooding of an underground dry mine. Two new underground mines are currently under construction. The Prairie Evaporite Formation accumulated during the Middle Devonian along an evaporating equatorial inland sea that extended onto the Laurentia paleocontinent. Development of a 400 km long reef at the northern seaward end barred the basin, permitting accumulation of up to 200 m of halite-dominated evaporite beds across north-central Alberta, southern Saskatchewan and into adjacent areas of the United States. Late cycle potassiumrich brines concentrated within the southern Saskatchewan sub-basin, resulting in accumulation of potash ore zones as the uppermost interval of the 100–200 m thick halite-anhydrite deposit. Early diagenetic processes resulted in widespread concentration of sylvite-rich beds upon leaching of Mg chloride from carnallite-rich deposits, resulting in commercially attractive potash ore. Subsequent post-burial dissolution of halite-dominated beds occurred across large areas of Alberta and southern Saskatchewan, including portions of the potash mining districts. Natural dissolution collapse-subsidence structures up to 10 s km long may have permitted some mining areas to be in contact with basin brines. Brines may have also mixed with descending groundwater sourced from Cretaceous strata up-section if the carbonate seals of the overlying Dawson Bay Formation were compromised by fracturing. Mining methodologies are designed to minimize the mine-scale subsidence upon ore removal and limit potential fracturing of overlying Dawson Bay limestone beds. Brine seeps into the underground mines vary from controllable nuisances to catastrophic flooding of underground workings. Remedial actions such as grouting generally control the seeps, but uncontrollable ingress has resulted in one underground operation being converted into a solution mine.

1. Introduction Annual global potash shipments are between 65 and 67 million tonnes. Canada, Russia, Belarus and China are the four largest potash producing countries, having a combined total of 75% of the world production. Southern Saskatchewan mines lead world production with an approximately 30% market share. Canada exports approximately half of its KCl production to the United States and half to the rest of the world with only 5% consumed domestically. Recent production of KCl by the southern Saskatchewan mines has been 16.78 Mt in 2014, 18.23 Mt in 2015, 17.90 Mt in 2016, 20.80 Mt in 2017 and 22.84 Mt in 2018 (Table 1). Economically attractive potash deposits of southern Saskatchewan have ore grades averaging between 20% and 30% K2O

(Funk et al., 2018a,b,c,d; Mosaic Corporation, 2016, 2017). Canada also has approximately one-third of the world reserves, estimated to last hundreds of years. This consists of 7–23 Bt KCl recoverable by conventional underground mining and another 70–100 Bt by solution mining (Berenyi et al., 2008). Potash-rich beds of the Middle Devonian Prairie Evaporite Formation were first discovered by Imperial Oil in 1942 during oil exploration activities in southeastern Saskatchewan, although the deposit had no commercial interest because of the 2 km depth of burial. Regional oil exploration activities in the 1950s confirmed that the potash-rich beds were widely distributed in Devonian strata across more northward areas of southern Saskatchewan with shallower depths of approximately 1000 m. These more attractive depths resulted in the

E-mail address: [email protected]. https://doi.org/10.1016/j.oregeorev.2019.103117 Received 1 February 2019; Received in revised form 1 September 2019; Accepted 8 September 2019 Available online 11 September 2019 0169-1368/ © 2019 Elsevier B.V. All rights reserved.

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Table 1 Annual KCl production of southern Saskatchewan potash mines in millions of tonnes. Data compiled from corporate annual reports and Saskatchewan Department of Mineral Resources. Company

Mine

Ore Zone

Operation

Depth

2014 Production (Mt)

2015 Production (Mt)

2016 Production (Mt)

2017 Production (Mt)

2018 Production (Mt)

Nutrien Nutrien Nutrien Nutrien Mosaic Nutrien K+S Mosaic Mosaic Nutrien Total (Mt)

Vanscoy Cory Patience Lake Allan Colonsay Lanigan Bethune Belle Plaine Esterhazy Rocanville

Patience Lake, Belle Plaine Patience Lake Patience Lake Patience Lake Patience Lake Patience Lake Belle Plaine Belle Plaine Esterhazy Esterhazy

Underground Underground Solution Underground Underground Underground Solution Solution Underground Underground

1000 m 1000 m 1000 m 1000 m 1000 m 1000 m 1500 m 1600 m 1000 m 1000 m

1.058 1.180 0.300 2.470 1.400 1.680

1.967 1.510 0.260 2.380 1.400 1.830

2.200 1.240 0.230 2.380 0.500 2.030

2.200 4.000 2.490 16.778

2.100 4.300 2.480 18.227

2.400 4.200 2.720 17.900

2.400 0.990 0.300 1.830 1.100 1.820 0.500 2.700 4.300 4.860 20.800

2.240 0.810 0.200 2.410 1.200 1.960 1.400 2.800 4.600 5.220 22.840

Burr

Patience Lake Colonsay

Jansen

Allan

Lanigan

Northern District

50

Wynyard

Southern District

Vanguard

km Bethune

Moose Jaw

Manitoba

Saskatoon

Vanscoy

0

wan Saskatche

Cory

K1 K3

Regina

Fig. 1. Potash mines (red) and important development projects (green) of the Northern (Saskatoon) and Southern (Regina) potash mining districts. Mines of the Northern District are: Vanscoy, Cory, Patience Lake, Allan, Colonsay, and Lanigan. Mines of the Southern District are: Bethune, Belle Plain to the west and Esterhazy K1, K2 and Rocanville to the east. Development projects and mine developments of the Northern District are: Burr, Jansen, and Wynyard. Projects of the Southern District are: Vanguard, Kronau, Milestone, and Esterhazy K3. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

K2

Rocanville Belle Plaine

Kronau Milestone

potash, resulting in large price swings with shifts in supply and demand (Fig. 3). Until 2008, the US dollars per tonne price held within the range of US$150–200, but a very steep price rise occurred in 2009 to US $800–900 per tonne. Increased production from operating mines and intense exploration activities across southern Saskatchewan followed, resulting in numerous new prospective land acquisitions and proposals for commercial development. A price collapse to US$300–400 occurred during the world-wide economic recession of 2009–2010. Price stabilization followed during 2012–2013 at this significantly lower level. Another steep price drop occurred in early 2013, in response to the collapse of the Russian-Belarusian potash cartel and voluminous production increase by Russian miners. Prices further declined to the US $200–225 per tonne range by 2016, resulting in widespread curtailment of Saskatchewan production and shelving of mine development projects. Increased demand during 2017–2018 resulted in a rise in annual Saskatchewan potash production from 18 Mt to more than 22 Mt. There is currently a rising price trend from near US$225 towards US$300 per tonne. This paper describes the stratigraphic framework for the southern Saskatchewan potash deposits, focusing on why potash mines are distributed across this area of western Canada and not elsewhere. This provides the context to discuss the origin and distribution of salt dissolution-induced collapse of overlying strata. These structures are observable near surface in Alberta at oil sand mines, and used to characterize similar structures distributed across the southern Saskatchewan potash mining areas where their morphogenesis could only be inferred

early mine developments during the 1960s. The commercially viable potash mines presently operating in Canada are located in southern Saskatchewan, and associated with deposits of the Prairie Evaporite Formation (Figs. 1 and 2). The Nutrien Ltd. mining operation in New Brunswick was recently closed because of lower cost of production from Saskatchewan mines. There are 11 producing mines in Saskatchewan (Fig. 1), recovering approximately 23 Mt of KCl (2018) from halite-sylvite ore (sylvinite) associated with the upper Prairie Evaporite Formation (Delaney, 2017). Of these, 8 mines are conventional underground operations at 900–1100 m depths. One mine, the Colonsay, was closed in 2019, but this was offset by initial production from the K3 Mine development. Solution mining with brine solvent methodology is used at 3 operations where the ore is buried to 1500–1600 m depths, or as remedial action responding to flooding of a previous underground dry mine. Almost all of the potash production from the Saskatchewan mines is controlled by two corporations, the Mosaic Company and Nutrien Ltd., which was formed upon the 2018 merger between the Potash Corporation of Saskatchewan and Agrium Inc. Aside from these mining conglomerates, there is the solution mine operated by K + S Potash Canada. It is the only new mine (2017) commissioned in Saskatchewan during the last four decades, although two more are in advanced stages of development. Otherwise, most prospective new sources of production resulting from widespread exploration activities a decade ago have been curtailed by the price collapse in 2016. The last two decades have recorded unusually volatile markets for 2

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Fig. 2. The Prairie Evaporite Formation, Devonian Elk Point Group, accumulated up to 200 m of halite-dominated beds across western Canada and into adjacent areas of northeastern Montana and western North Dakota. Post-burial structural trends controlled the salt dissolution patterns in the foreland Alberta and intracratonic Williston constituent basins of the Western Canada Sedimentary Basin. A 1000 km long and 150 km wide dissolution trend developed along the up-dip basin margin with removal of up 100–150 m of salt interval. A second regional dissolution trend resulted in removal of up to 200 m of halite-anhydrite section across the southern Saskatchewan area of the northern Williston Basin. Collapse structures along these regional salt removal trends, including large areas of the potash mining districts (blue outlines), were rejuvenated during the Pleistocene. Subglacial meltwater flows occurred to depths of 1000–1500 m, and came in contact with the salt beds. Modified from Broughton (2017a, c, 2018). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

1–2 year long periods to permit remedial actions such as extensive grouting and dewatering. For example, a nearly uncontrollable flooding at the Rocanville Mine necessitated closure for a year. In the extreme case, an eventually uncontrollable flood forced abandonment of underground operations at the Patience Lake Mine and necessitated conversion into a solution mine. 1.1. Data sources The economic importance of potash-rich beds in southern Saskatchewan has resulted in numerous reports on regional stratigraphy by various government related institutions, such as the Saskatchewan Geological Survey, Saskatchewan Research Council and university departments. Saskatchewan Geological Survey publications provide an overview of the regional-scale depositional trends. Some annual corporate reports discuss mine-scale geology with descriptions of mine design and capacity and production statistics relating to specific ore zones. This paper illustrates geologic maps of the potash-rich members of the Prairie Evaporite Formation to provide geologic context for the 11 mines currently in production. Mine specific production data are available from corporate annual reports. Descriptions of ore geology of individual mines, particularly those controlled by the Mosaic Company, are mostly proprietary. Potash production statistics are reported in two related formats: (1) production of KCl from sylvinite, and (2) finished product as the amount of K2O chemical equivalent for manufacture of fertilizer. Mine production and reserves are reported as KCl in millions of tonnes (Mt).

Fig. 3. Potash price trends in US dollars per tonne, spot Vancouver export. Modified from Delaney (2017) and Index Mundi-Commodities.

from seismic imaging and sparse drill hole information. These observations provide insight into how brine seeps result in geohazards that variously impact most of the southern Saskatchewan potash mines. Both natural dissolution and salt removal by mining may result in structural displacements that can potentially compromise the integrity of seals created by limestone beds above mine workings. Communication between potash beds and overlying Cretaceous aquifers have resulted in brine seepage events into underground workings. These seeps vary from controllable nuisances to near-floods and uncontrollable catastrophic events (Wittrup and Kyser, 1990). Voluminous ingress events have forced temporary closure of several mines for 3

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Ore grade and finished manufactured product are reported as percentage of K2O content equivalent. Chemically pure KCl, also known as muriate of potash (MOP), contains approximately 62% K2O equivalent. This paper focuses on KCl production by specific mines as related to the stratigraphic context of the ore zone. Production statistics for finished product by surface facilities, reported as K2O equivalent, are not reviewed, but such data can be obtained from corporate reports.

syndepositional process (Wardlaw, 1968; Holter, 1969; Meijer Drees, 1986, 1994). Fluid inclusion studies have provided additional support to the interpretation that post-burial formation of sylvite also resulted from alteration of carnallite during orogenic events. Various basin deformation stages and flows of basin water resulted in widespread and pervasive recrystallization fluids during the Late Devonian (Wardlaw, 1968), but also during basin deformation events at the end of Paleozoic (Antler) and during the Jurassic-Cretaceous (Laramide). For example, potassium-argon dates on sylvite indicate a range of dates for potential diagenetic alteration of carnallite to sylvite as late as the Permian and Mississippian (Koehler et al., 1990; Koehler, 1997). The ore rock, sylvinite, consists of mixtures of halite and sylvite. Sylvinite typically consists of 30% sylvite and 65% halite with 4–5% insoluble residue (Funk et al., 2018a,b,c,d). Carnallite is considered a contaminant in potash ore as it lowers overall grade and impacts mill recovery. The presence of carnallite is often only a minor component, but may locally constitute up to 4–6% of the ore. Carnallite content often increases along margins of halite-sylvite ore zones as the result of secondary leaching and remobilization of the Mg-chloride brines (Wardlaw, 1968; Holter, 1969). A comparison of the proportions of carnallite and sylvite in a region of carnallitite with an adjacent area of sylvinite suggests that the amount of sylvite present corresponds to the amount which could be derived from carnallite by leaching of magnesium chloride (Wardlaw, 1968). The carnallite-sylvite transformation results in a volumetric change that may be indicated by seismic profiles.

2. Origin of potash: Oceanic water and epicratonic basin evaporites Extensive potash mineral deposits accumulated during the Paleozoic-Mesozoic at various world-wide locations because of seawater chemistry that differs from modern oceans. Modern oceans apparently reflect a compositional change in seawater chemistry that evolved throughout the Phanerozoic (Garrett, 1995; Hardie, 1996). This resulted in a shift from calcite-dominate seawater forming potasharagonite to seawater capable of forming gypsum-rich evaporites. The reasons for this transition are uncertain, but may be related to the rise of mid-oceanic ridges that resulted in hydrothermal brine flux linked to oceanic crust production (Hardie, 1996). The appearance of evaporitic potassium chloride mineralogy during the Paleozoic and Mesozoic coincided with elevated sea-levels, in contrast with modern aragonite-rich oceanic conditions. It is notable that there are no present-day K-Mg saltforming deposits accumulated along marginal marine basins at the scale of such deposits in the Phanerozoic geologic record. Volumetrically significant deposits from seawater consist of carbonates followed by sulphates then chlorides. The sequencing of mineral precipitates from variously saturated seawater results in: (1) Ca-carbonate, Ca-sulfate and Na-chloride, (2) Na-Mg sulphate without K salts, (3) sylvite, (4) carnallite, and (5) magnesium chloride. Commonplace mineral assemblages consist of sylvite, carnallite, langbeinite, kainite, and polyhalite. Potassium and magnesium salt deposits resulting from seawater evaporation are comparatively rare (Garrett, 1995; Bąbel and Schreiber, 2014). Mixtures of halite, sylvite and carnallite dominate the mineralogy of western Canadian potash deposits.

3. Regional geology The commercially important Middle Devonian potash deposits of western Canada accumulated as beds of the upper Prairie Evaporite Formation, Elk Point Group (Fig. 4) across the southern Saskatchewan area of the intracratonic Williston Basin (Fig. 2), which extends across large areas of western Canada and southward into eastern Montana and western North Dakota (Holter, 1969; Meijer Drees, 1986; LeFever and LeFever, 2005; Broughton, 2018). The southern Saskatchewan area was favorable for the up-section accumulation of halite-sylvite-carnallite facies as a late stage evaporitic mineral sequence following more widespread limestone-dolomite and gypsum-anhydrite deposition along the length of the Elk Point/Prairie Evaporite basin. These carbonateevaporite cycles were regulated by periodic influxes of seawater into the epicratonic evaporite basin.

2.1. Diagenesis and sylvite-carnallite mineral sequencing Mixtures of sylvite and halite, a combination referred to as sylvinite, is the commonplace ore rock of the southern Saskatchewan mines. The potash-rich members of the upper Prairie Evaporite Formation are characterized by beds with abrupt lateral and vertical changes from carnallite-halite (carnallitite) to sylvite-halite (sylvinite). This resulted in the commonplace occurrence of sylvinite beds overlying carnallitite beds. This sylvite-carnallite relationship is enigmatic because this ancient rock sequencing record is not consistent with mineralogical sequencing observed with evaporation of modern seawater. It is the reverse order of normal salt mineral sequencing. It has been widely interpreted that formation of sylvite-rich beds was a diagenetic process that resulted in primary carnallite having been leached of magnesium chloride content during early burial (Wardlaw, 1968; Garrett, 1995; Bąbel and Schreiber, 2014). Studies of the diagenetic petrofabrics are supported by interpretations of trace element distributions. For example, bromide distribution in the chloride minerals indicates that the red coloured sylvinite formed by leaching of the magnesium chloride from carnallite (Wardlaw, 1968; Yang, 2016). In contrast, stratified halite deposits offset from the potash ore zones retain primary depositional fabrics such as elongated chevron habit crystalline textures. Replacement petrofabrics indicate formation of red sylvite after carnallite, wherein the iron-oxide inclusions of the carnallite were inherited by the sylvite fabrics. Potassium salts are interpreted to have formed as precipitates immediately below the sediment-brine interface with diagenetic alterations following shallow burial and groundwater flushing. Diagenetic alterations of carnallite to sylvite were thereby essentially a

3.1. Evaporite basin and the Presqu'ile barrier reef During the Devonian, the Laurentia and Gondwana paleocontinents were separated by the Rheic Ocean, which was closed by the Mississippian (Fig. 5). These Paleozoic movements resulted in compressional and extensional Antler orogenic tectonism across protowestern North America as the two continental masses collided to form Pangaea (Mossop and Shetsen, 1994). During the Middle Devonian, a southward trending arm of the Panthalassic Ocean embayed the northern equatorial margin of Laurentia. A shallow sea extended from the present-day position of northern Alberta, across southern Saskatchewan and into eastern Montana and western North Dakota (Fig. 4). The 400 km long Presqu'ile barrier reef in northern Alberta developed during the Lower-Middle Devonian (Givetian Stage) at the northern seaward end of the shallow inland sea, resulting in a barred evaporite basin (Meijer Drees, 1986; Holter, 1969; Broughton, 2017a,b,c). Paleogeographic reconstruction suggests that the Devonian position of the Elk Point Basin was at latitudes of 10° to 20° S (Van der Voo, 1988). This equatorial paleogeography (Fig. 5) was favorable for evaporation cycles that resulted in up to 200 m of halite-dominated salt beds, represented by the Prairie Evaporite Formation, Elk Point Group. Fluid inclusion studies of Prairie Evaporite salts indicate brine temperatures up to 39 °C, consistent with the equatorial position of the Elk 4

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Fig. 4. Stratigraphy of the Devonian Elk Point Group of northern Alberta/Northwest Territories, Alberta, and southern Saskatchewan. Modified from Grobe (2000).

anhydrite and calcareous mudstone across central Alberta and most of southern Saskatchewan. The NaCl-dominated deposits pass up-section to NaCl-KCl-dominated uppermost beds of the Prairie Evaporite (Fig. 2). Mesozoic Cordilleran and Laramide tectonism broadly structured this Middle Devonian salt basin across western Canada into regional sub-basins eastward of the Rocky Mountain uplands, forming the foreland Alberta Basin and the intracratonic Williston Basin (Holter, 1969; Kent and Christopher, 1994; Schneider and Grobe, 2013; Broughton, 2018). The basins accumulated multi-km thick successions of Cretaceous sediments shed from elevated Rocky Mountain terrains. The Sweetgrass Arch in eastern Montana and its northern extension into Alberta, known as the Bow Island Arch, separated these two constituent basins of the overarching Western Canada Sedimentary Basin (Fig. 2). Partition by the Arch was followed by erosion across the centralnorthern Alberta foreland during the Middle Jurassic-Early Cretaceous Cordilleran orogeny, resulting in deposition of Early Cretaceous sediments on a karstic paleotopographic terrain of Devonian carbonate. In contrast, a more continuous record of sedimentation to the southeast filled the intracratonic Williston Basin. Approximately 5 km of strata accumulated, which were preserved at the depocenter in western North Dakota during intermittent subsidence since the Late Cambrian. Responses to movements by orthogonal basement blocks helped to configure both the Alberta and Williston Basins (Kent, 1974; Thomas, 1974; Brown and Brown, 1987). The dominance of NW–SE and NE–SW structural trends resulting from basement block movements extended from the Williston Basin depocenter in western North Dakota outward to the basin margins including southern Saskatchewan. As the basin subsided, differential displacement by the craton blocks resulted in lineaments oriented NW and NE that variously emanated upward during deposition of Paleozoic to Cretaceous strata (Broughton, 1977, 1985, 2017a, 2018 and references therein). Glacial erosion events during the Pleistocene resulted in relatively shallow burial, 100 s m to 1–1.5 km, of Prairie Evaporite strata across central Alberta and southern Saskatchewan.

Fig. 5. Paleogeography of the Devonian Elk Point Basin. A shallow inland sea that extended across the Laurentia continental land mass from northern Alberta, across southern Saskatchewan, and into eastern Montana and western North Dakota. The Presqu'ile barrier reef across the northern seaward end of this inland sea barred the basin and permitted accumulation of up to 200 m of halite and anhydrite beds. KCl-rich brines were concentrated within the southern Saskatchewan sub-basin, resulting in potash deposits of the upper Prairie Evaporite Formation. Modified from Broughton (2017c, 2018).

Point Basin during the Middle Devonian (Chipley and Kyser, 1989, 1991; Chipley, 1995; Yang, 2016). The evaporite basin fill consists mostly of halite (40–80%), variously mixed and interbedded with 5

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clastics of the Contact Rapids Formation and other equivalent strata as the uppermost interval of the Lower Elk Point Group (Fig. 4).

3.2. Prairie Evaporite stratigraphy Strata of the Prairie Evaporite Formation accumulated as a regionally uniform succession up to 200 m thick across southern Saskatchewan and central Alberta (Figs. 2 and 4), and southward into adjacent areas of northeastern Montana and western North Dakota (Meijer Drees, 1994; Grobe, 2000). The Whitkow Salt Member accumulated as lateral equivalents of the uppermost Winnipegosis Formation. The stratigraphically higher Shell Lake Member consists of anhydrite and dolostone beds (Fig. 4). The overlying Leofnard Member consists of halite beds with subordinate dolostone, anhydrite and mudstone. Basin-wide deposits of the uppermost Leofnard Member pass laterally into potash-rich equivalent members distributed across southern Saskatchewan and parts of western North Dakota (Meijer Drees, 1986). Leofnard Member strata, and the potash-rich members, were covered by an evaporitic cycle consisting of the Second Red Bed, Dawson Bay Formation and stratigraphically equivalent Hubbard Evaporite. Detailed regional stratigraphy of the Prairie Evaporite Formation has been documented for Alberta (Hamilton, 1971; Meijer Drees, 1986, 1994; Grobe, 2000), Saskatchewan (Holter, 1969; Yang et al., 2009a,b,c,d, Yang et al., 2008a,b,c), and Manitoba (Bezys et al., 2008a,b). Different stratigraphic nomenclature is used on either side of the Alberta-Saskatchewan provincial boundary. The Geological Survey of Alberta designates the upper Elk Point Group as including the Dawson Bay Formation and the two Red Beds. The Saskatchewan Geological Survey does not include these strata within the upper Elk Point Group, and designates the interval as part of the overlying Manitoba Group such that the top of the upper Elk Point Group is the base of the Dawson Bay Formation (Meijer Drees, 1986, 1994; Oldale and Munday, 1994).

3.2.2. Upper Elk Point Group Early Upper Elk Point Group sediments accumulated as a broad carbonate platform represented by the Keg River Formation across northern Alberta, and the equivalent Methys Formation-Winnipegosis Formation across central Alberta and southern Saskatchewan. The Upper Keg River strata to the west and the Methys Formation to the east included dolomitized biohermal mounds and pinnacle reefs up to 80 m thick (Fig. 4). Salt beds of the overlying Prairie Evaporite Formation drape these high relief mounds, which assert important post-burial controls on salt removal patterns. Three Middle Devonian carbonate-evaporite depositional cycles are represented by the Upper Elk Point Group across southern Saskatchewan and westward into north-central Alberta (Lane, 1959; Bebout and Maiklem, 1973; Kendall, 1975; Dunn, 1976, 1982; Fuzesy, 1982, 1984). In Saskatchewan, the first cycle occurred with deposition of Winnipegosis Formation limestone, passing upward into the Prairie Evaporite Formation. Commercially attractive potash beds occur in the uppermost interval. Unconformable deposits of the second cycle accumulated as the Dawson Bay Formation, a succession represented by the Second Red Bed and limestone, and the Hubbard Evaporite. The third cycle consists of limestone, shale and evaporite beds represented by the Davidson Member of the Lower Souris River Formation, which consists of the First Red Bed, followed by the Davidson Evaporite (Fig. 4). The Elk Point Group was succeeded by Middle-Upper Devonian strata of the Beaverhill Lake Group, consisting of up to 200 m of limestone and calcareous siltstone (Schneider and Grobe, 2013). The evaporative cycle towards the center of Saskatchewan sub-basin resulted in concentration of the potassium-rich brines. Contemporary regional structures such as the Peace River-Athabasca Arch in northern Alberta and the Meadow Lake Escarpment in south-central Saskatchewan regulated the flow of seawater into the evaporite basin. Intermittent ruptures or overflows of seawater across the Presqu'ile barrier reef permitted seawater to transgress to the southeast. The mineralogy of the evaporite deposits was responsive to differing water depths during deposition of the upper Prairie Evaporite Formation, resulting in accumulation of a 60 m thick interval of potash-rich beds. In contrast, replenishment by seawater sourced from the northwest inhibited precipitation of the potash mineral sequences (Hamilton, 1971; Maiklem, 1971; Hamilton and Olson, 1994). This resulted in extensive regional precipitation of halite and distribution of halitedominated beds across Alberta, in contrast to potassium-rich mineral accumulations across southern Saskatchewan (Holter, 1969). Only marginal potash deposits occurred in adjacent areas of Alberta (Eccles et al., 2009), Manitoba (Bannatyne, 1983; Bamburak and Nicolas, 2009; Nicolas, 2015) and North Dakota (LeFever and LeFever, 2005; Kruger, 2014).

3.2.1. Lower Elk Point Group The Lower Elk Point Group is represented by salt beds of the Lotsberg Formation (Emsian), and overlying Cold Lake Formation (Eifelian) (Fig. 4), which were preserved in north-central Alberta along structural lows developed between the Meadow Lake Escarpment to the southeast in southern Saskatchewan and the Peace River Arch and Tathlina Uplift to the northwest in central and northern Alberta (Grobe, 2000). Salt beds of the Lotsberg and Cold Lake Formations of the Lower Elk Point Group accumulated onto the ancestral North American craton because of restricted circulation between the inland seaway and open oceanic conditions. The low bromine content of these salt deposits indicates that the salt deposits were at least partially impacted by meteoric-charged groundwater, resulting in dissolution and subsequent deposition of relatively pure halite (Wardlaw and Watson, 1966). These central Alberta salt beds underlying the pervasive Prairie Evaporite have no salt-bearing stratigraphic equivalents across southern Saskatchewan (Fig. 4). The reasons for this remain uncertain. It may have been because the geographically restricted salient of sea water extending southward into Alberta did not extend southeast across southern Saskatchewan. This may have resulted from the build of elevated reefs along the Meadow Lake Escarpment, a pre-Devonian carbonate platform extending across southern Saskatchewan that did not extend westward into the central Alberta Basin (Holter, 1969; Meijer Drees, 1986, 1994). However, maps of the Prairie Evaporite Formation do not indicate significant development of reef trends in the substrate that would have controlled this depositional pattern. In the alternative, accumulation of Lower Elk Point Group salt beds may have been controlled by regional structure related to the extension of the Sweetgrass Arch into Canada. This would have resulted in early stage partition of the Elk Point evaporite basin with ancestral depositional centers subsequently developed as the Alberta and Williston Basins (Kent and Christopher, 1994; Eccles et al., 2009; Broughton, 2018). This regional structure would have to some extent controlled seawater volumes and water depths of the Elk Point Basin prior to the Presqu'ile barrier reef. The Emsian-Eifelian carbonate-evaporite succession was covered by

4. Potash members In Saskatchewan, the upper 60 m interval of the Prairie Evaporite Formation includes four stratabound potash-bearing members (Figs. 6 and 7). These sylvite-rich intervals are each commonly 6–15 m thick, and separated by up to 45 m intervals of halite-dominated, sylvite-poorstrata. These Members are, in ascending order: Esterhazy, White Bear, Belle Plaine and Patience Lake. Only the White Bear Member has poorly developed potash beds that are not commercial (Holter, 1969; Fuzesy, 1982, 1984; Yang et al., 2009a,b,c,d, Yang et al., 2008a,b,c). Commercially attractive ore grades for the potash members typically average between 22% and 25% K2O. A representative histogram based on nearly 40,000 samples collected from the Esterhazy Member at the Rocanville Mine indicates an average mean grade of 23.4% K2O (Fig. 8). A halite-dominated non-ore interval is referred to as a salt-back 6

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Saskatchewan

Manitoba

Hubbard Evaporite

West

East Dawson Bay Fm.

Win

Prairie Evaporite

LEGEND Limestone Dolomite Evaporite Potash Calcereous Shale

nip

ego

sis

Fm

.

Ashern 0

50

100

km

T

0 m

Patience Lake Member Belle Plaine Member White Bear Member Esterhazy Member

15 30

PLM BPM WBM EM

Fig. 6. Diagrammatic cross-section of the Devonian Elk Point Group across southern Saskatchewan with westward back-stepping potash-rich members of the upper Prairie Evaporite Formation. Modified from Fuzesy (1982).

(3) halite interval 17 m thick, (4) Belle Plaine Member with 6 m of sylvinite, (5) halite interval 2 m thick, (6) Patience Lake Member with 12 m of sylvinite, and (7) halite interval 10 m thick (Fig. 7). Westward back-stepping deposition occurred from the lowermost Esterhazy to the uppermost Patience Lake members (Fig. 6) (Yang et al., 2009a,b,c,d; Yang et al., 2008a,b,c). Ore zones in southern Saskatchewan are typically overlain by approximately 500 m of Devonian carbonate, 500 m of Cretaceous sandstone and shale, and a variable thickness of Quaternary sediments

when it directly overlies a mine room. Thickness of a salt-back varies from a few up to 30 m, and as much as 60 m in some areas. The saltback is thickest in areas where the White Bear or Belle Plaine members are absent (Yang et al., 2009d,e,f,g). Typical exploration and development wells on a southern Saskatchewan mining lease penetrating strata of the Prairie Evaporite Formation would encounter a stratigraphic succession of beds represented in ascending order by: (1) a lowermost interval of a regionally thick halite bed, (2) Esterhazy Member with 8 m of sylvinite,

Fig. 7. Representative potash-rich members of the upper Prairie Evaporite Formation in a reference well located at 121/07–29-17-20W2M. Modified from Yang et al. (2009d), Saskatchewan Geological Survey. 7

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Fig. 8. Histogram of ore grade sampled from the Esterhazy Member at the Rocanville Mine.

to 23 m thick and grades up to 33% K2O accumulated across Twp. 38, Rge. 4, W3M (Yang et al., 2009b, 2018b). A 6–13 m thick trend extends from near the city of Saskatoon to the southeast into the area of the city of Yorkton. A trend with greater than 6 m can be followed across Twp. 12–42, Rge. 30, W1M into Rge. 2, W3M. (Yang et al., 2009b, 2018b). This thick trend follows a similar trend in the underlying Esterhazy Member (Yang et al., 2018a). The ore of this Member is a favorable target for solution mining where the depth increases to 1,500 m across southernmost Saskatchewan, such as near Regina.

(Fig. 6). The potash-rich members of the upper Prairie Evaporite thin southward, and structurally deepen to between 1,700 m and 3,600 m toward the Williston Basin depocenter in western North Dakota (Garrett, 1995). 4.1. Esterhazy Member The potash-rich Esterhazy Member averages 9 m thick, but is often up to 20 m and reaches a maximum thickness of 26 m in Twp. 18, Rge. 23, W2M (Fig. 9) (Yang et al., 2009a, 2018a). A 15–20 m thick trend extends from northwest to the southeast of Yorkton. The interval is typically 7–13 m thick across southeastern Saskatchewan mine sites such as at the K1, K2, Rocanville, Belle Plaine and Bethune Mines (Fig. 1). In contrast, the interval has near zero thickness across the western areas of the potash mining area, such as in the vicinity of the Vanscoy, Cory, Patience Lake, Allan, Colonsay and Lanigan Mines (Fig. 1). The Esterhazy Member is separated from the overlying White Bear Member by a salt-back interval consisting of halite and low-grade sylvinite. The sylvinite ore zone is commonly 2.5–3.5 m thick. The ore zone is generally thinner with a lower average grade up to 20% K2O compared to ore zones of the overlying members (Holter, 1969). Carnallite mineralization can be as high as 6%, but mostly occurs with a patchy distribution. There is a lower average percentage of insoluble residues in this member compared with other members. The overall lack of clay beds in the mining sites to the east facilitates rooms with more stable salt-backs that roof the workings, permitting wider excavations.

4.4. Patience Lake Member This uppermost potash-rich Member is typically 3–18 m thick. Mean thickness is 11 m. The Patience Lake Member is separated from the Belle Plaine Member by a 3–12 m thick salt-back interval (Yang et al., 2009e,f,g). The Member thickens to 20 m or more across the mining area near the city of Saskatoon, and increases to as much as 30 m in some areas such as Twp. 35, Rge. 26, W2M (Yang et al., 2009c, 2018c). The Member thickens regionally as two parallel trends (Fig. 11). The northern trend, 16–25 m thick, extends from Saskatoon to the southeast towards but not as far as the city of Yorkton (Yang et al., 2018c). This northern trend overlies a similarly thick trend that developed in the underlying Esterhazy and Belle Plaine Members. A southern trend, 13–22 m thick, developed to the northwest and southeast of the city of Regina. The Patience Lake Member is typically characterized by two mineable ore zones (Fig. 12). The 7–14 m thick upper interval has higher grade ore averaging 22–25% K2O with insoluble residues averaging 5%. The lower interval ore is thinner, typically 3.5–5 m. The upper Patience Lake generally lacks carnallite, in contrast to patchy distribution of this contaminant in the lower zone. The 1–2 to 10–20 cm thick clay beds in the upper part of the ore zone interval that could impact roof stability are removed.

4.2. White Bear Member The strata of this Member are between the Esterhazy Member and the overlying Belle Plaine Member. The interval is characterized by a patchy distribution of low grade sylvinite and halite, and widely distributed clay beds. The thickness increases to as much as 10 m in southeastern Saskatchewan, but more often the Member is only a marker horizon traceable across the potash mining areas. The Member is not a commercially attractive mining target.

5. Regional dissolution trends Dissolution removal of the salt section at depth and subsequent impact on overlying strata have resulted in structural trends that overprint the Paleozoic and Mesozoic stratigraphic successions across large areas of the northern Williston Basin (Broughton, 1985, 2017a,b; Chairawiwut, 2015). The 500 m thick interval of overlying Upper Devonian and Cretaceous strata has been selectively cross-cut by faults and fracture zones that extended upward from the level of salt

4.3. Belle Plaine Member The thickness across southern Saskatchewan is mostly less than 4 m to the west but increases to the east- southeast to 6–13 m or more. The mean thickness is 7 m (Fig. 10). For example, a sylvite-rich interval up 8

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Fig. 9. Thickness (m) of the Esterhazy Member across southern Saskatchewan. Mines currently in production are: (1) Vanscoy, (2) Cory, (3) Patience Lake, (4) Allan, (5) Colonsay, (6) Lanigan, (7) Esterhazy K1, (8) Esterhazy K2, (9) Rocanville, (10) Belle Plaine, and (11) Bethune. Modified from Yang et al. (2009a, 2018a).

migrated to the southwest along shallowly buried Devonian carbonate strata such as the Keg River/Winnipegosis Formations. Flows were particularly directed along the 10 s km long margins of Keg River/ Winnipegosis reef trends and thence upward into overlying salt beds. Flows up-section into overlying salt beds resulted in the regional dissolution trends and collapse-subsidence of overlying strata that were oriented to the NW and to the NE, paralleling reef trends that followed the boundaries of underlying cratonic blocks. These salt dissolution patterns across the southern Saskatchewan area of the northern Williston Basin developed in stages throughout the Phanerozoic, mostly responsive to uplift and erosion during ancestral movements of the intracratonic Williston Basin. Many authors, such as Holter (1969), McTavish and Vigrass (1987) and Broughton (2017c, 2018), interpreted a widespread stage of salt removal at the end of Paleozoic during the latest Mississippian and into the Early Triassic that occurred during a regional uplift (sub-Watrous unconformity). A Middle Jurassic to Early Cretaceous uplift (sub-Manville unconformity) similarly resulted in widespread salt removal patterns. Moreover, late stage development of the Williston Basin during Jurassic-Cretaceous tectonism resulted in widespread salt removal patterns and collapse structures across southern Saskatchewan. Two significant basin-scale salt dissolution trends developed, each 100 s of km long, consisting of partial to complete dissolution of the 100–200 m thick halite-dominated salt interval (Smith and Pullen, 1967; Holter, 1969; Fuzesy, 1982, 1984; McTavish and Vigrass, 1987; Anderson and Knapp, 1993; Anderson and Hinds, 1997; Meijer Drees,

dissolution removal, resulting in differentially subsided and rotated fault blocks and fracture zones that extend upward to near-surface levels. Groundwater flow patterns associated with regional salt dissolution collapse-subsidence structures were consistent with Laramide deformation of the Williston Basin. Flows along permeable Devonian Winnipegosis/Keg River carbonate strata followed basement lineaments (Kent, 1974; Kent and Christopher, 1994; LeFever and LeFever, 2005; Broughton 2017a). Paleozoic formation waters within the Keg River/Winnipegosis strata migrated upward into the overlying Prairie Evaporite, resulting in removal of overlying salt beds (LeFever and LeFever, 2005). These groundwater flow patterns and contiguous salt removal trends were strongly aligned along reef margins in the Keg River/Winnipegosis, where orientations were largely controlled by basement lineaments responding to subsidence of the ancestral Williston Basin (DeMille et al., 1964; Holter, 1969; LeFever and LeFever, 2005; Broughton, 2017a). Recharge areas for the Williston Basin, such as the Montana Uplift and the Black Hills, resulted in hydrogeologic drives that controlled deep basin water flows up-section to the northeast toward topographically lower discharge areas in southern Saskatchewan and southwestern Manitoba, paralleling the erosional edge of mostly Devonian strata on the Canadian Shield (Garven and Freeze, 1984; Garven, 1989; Grasby and Chen, 2005). Flows to the northeast mixed with influxes of surface-charged groundwater during periods of basin uplift. Connate water from basin loading mixed with groundwater that 9

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Fig. 10. Thickness (m) of the Belle Plaine Member across southern Saskatchewan. Mines currently in production are: (1) Vanscoy, (2) Cory, (3) Patience Lake, (4) Allan, (5) Colonsay, (6) Lanigan, (7) Esterhazy K1, (8) Esterhazy K2, (9) Rocanville, (10) Belle Plaine, and (11) Bethune. Modified from Yang et al. (2009b, 2018b).

carbonate platform. Flows up-section migrated into the overlying salt beds, resulting in brine- filled dissolution-collapse chimneys, 10 s m wide and 10 s to 100 s m high. They cross-cut the Prairie Evaporite Formation and extend upward into overlying strata. For example, Fig. 13A illustrates a 3D seismic image of a 100 m high structure that developed adjacent to the Lanigan Mine (Nemeth et al., 2002). Similar collapse chimneys have been observed throughout the potash mining areas. Many of the Paleozoic and Mesozoic salt collapse structures that were reactivated during the Pleistocene have a significant impact inthe potash mining areas. Deep basin water flows to the northeast toward the Alberta and Williston basin margins mixed with subglacial meltwater flows into the subsurface (Grasby and Betcher, 2000; Grasby et al., 2000; Broughton, 2017c, 2018). These mixed water sources came into contact with shallowly buried Devonian strata, including the Prairie Evaporite Formation salt interval (DeMille et al., 1964; Ford, 1997). Meltwater flows into the subsurface to depths as much as 1000–1500 m came in contact with shallowly buried Prairie Evaporite beds. Areas of the northern (Saskatoon) mining district were significantly impacted because the salt beds were sufficiently shallow to permit contact with the deeper subsurface meltwater flows. Isotope data of groundwater and mine seeps suggest that depleted meteoric water in a Cretaceous Mannville aquifer overlying the potash mines mixed with subglacial meltwater at a depth of 800–900 m or more (Grasby and Betcher, 2002; Grasby and Chen, 2005; Hendry et al., 2013). These flows also mixed with salts derived from the Prairie

1994; Broughton, 1997, 1985, 2017a,b,c, 2018; Palombi, 2008; Woroniuk et al. 2019). Models suggest that salt dissolution patterns resulted mostly or entirely from compaction-driven vertical water flows within the Devonian strata responsive to basin loading (Bachu and Underschultz 1993; Bachu et al., 1993; Bachu, 1995, 1999). All of these hypogene and epigene salt removal processes may have contributed to the widespread dissolution patterns in the halite salt basin, but the relative contribution and timing by each process remain uncertain (Broughton, 2017a,b,c, 2018). The resulting salt dissolution and subsidence of overlying strata configured the post-Devonian structure across large areas of western Canada and adjacent areas of northern United States. A 1000 km long, 150 km wide trend along the eastern up-dip margins of the Alberta and Williston Basins coincides with the eastern margin of the Western Canada Sedimentary Basin. This dissolution trend extends from northeastern Alberta, across southeastern Saskatchewan, and into southwestern Manitoba (Fig. 2). The second regional salt dissolution trend developed across the width of the southern Saskatchewan area of the northern Williston Basin, and extends southward into northeastern Montana and western North Dakota (Fig. 2). Both trends impact potash mining areas of southern and central Saskatchewan. These halite and halite-anhydrite dissolution trends developed large, 10 s km long, regional collapse-subsidence structures that impacted post-Devonian strata within and beyond the potash mining areas. Collapse-subsidence structures and fracture networks developed above margins of reef trends of the Winnipegosis Formation 10

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Fig. 11. Thickness (m) of the Patience Lake Member across southern Saskatchewan. Mines currently in production are: (1) Vanscoy, (2) Cory, (3) Patience Lake, (4) Allan, (5) Colonsay, (6) Lanigan, (7) Esterhazy K1, (8) Esterhazy K2, (9) Rocanville, (10) Belle Plaine, and (11) Bethune. Modified from Yang et al. (2009c, 2018c).

ratios and TDS evidence suggest that the invasion by glacial meltwater into the shallow subsurface occurred to depths of 500 m to as much as 1000–1500 m and extended in the subsurface to the southwest as far as 300 km from the basin edge, including large areas of the two potash mining districts (Fig. 2) (Grasby and Betcher, 2000; Wittrup and Kyser, 1990; Hendry et al., 2013; Woroniuk et al., 2019). Differentially subsided fault blocks resulted in larger areas of salt removal-collapse extending 100 s m upward to configure the subglacial topography. These 10 s km2 topographic configurations across southern Saskatchewan potash districts are known as Lows (Fig. 14). The collapse of a 100 s m thick section of post-Devonian strata resulted in topographic lows on the subglacial topography that were infilled by Late Pleistocene and Holocene surficial deposits. These structures are distributed across both the southern and northern potash mining districts. Examples of large 10 s km2 collapse structures are the Saskatoon Low (Fig. 14), Rosetown Low and Regina Low. All of these are Mesozoic structures that were reactivated during the Pleistocene configured the Quaternary topography (DeMille et al., 1964; Christiansen, 1967; Ford, 1997; Christiansen and Sauer, 2002; Broughton, 2017c, 2018). For example, the Saskatoon Low is a 40 km long and 25 km wide structural depression located south of the city. It has 200 m of relief on the Cretaceous structure (Fig. 12), resulting from removal of a 200 m thick section of salt (Christiansen, 1967). The staged salt removal impacted the: (1) Upper Cretaceous Lea Park, Judith River, and Bearpaw Formations of the Montana Group; (2) Early and Middle Pleistocene Mennon, Dundurn, and Warman Formations of the Sutherland Group;

Evaporite, accessed along karst collapse faults that cross-cut Cretaceous strata (Wittrup and Kyser, 1990; Gendzwill and Stauffer, 2006). The hydraulic head driving influxes of subglacial meltwater into the shallow subsurface was responsive to the 1.5–2 km thick Laurentide ice sheet during the glacial maximum (~25–40 ka), and to a lesser extent to proglacial meltwater during retreat of the ice sheet (~8–12 ka). The hydraulic head behind the glacial meltwater flow into the subsurface was sufficient to halt and to some extent reverse the regional water flow up-structure to the northeast toward the eastern margin of the Williston Basin (Grasby and Betcher, 2000; Grasby et al., 2000; Grasby and Chen, 2005; Broughton, 2017c). The flow up-section to the northeast toward the eastern basin margin was reasserted following glacial retreat, often resulting in discharge as saline springs along river valleys. Salinity data indicate that a chemical boundary developed between saline and fresh water flows in the subsurface across the northern Williston Basin areas of southern Saskatchewan and southwestern Manitoba. This resulted in a geochemical and hydrologic divide between Williston Basin deep aquifer water flow up-structure to the northeast, and southwestward flow down-dip into the subsurface by strongly pressured subglacial meltwater. The geochemistry indicates the extent to which fresh glacial meltwater mixed with the Devonian saline formation water that flowed up-structure to the northeast, and is consistent with the distribution of total dissolved solids. The geographic range of these meltwater influxes into the subsurface may be approximated by the 2000 mg/liter boundary (Betcher et al., 1995; Grasby and Betcher, 2000; Grasby et al., 2000; Grasby and Chen, 2005). Isotope 11

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Depth (KB)

when the sylvinite has been altered by partial to complete removal of the sylvite and replacement with crystalline halite. The leaching of potassium minerals at these zones concentrates halite without disrupting bed stratification. No disconformities result, although bed thinning may occur because of the sylvite deficiency. Sizes of these leach structures vary up to 100 s m long and 10sm wide and result in dead zones within an ore trend (Keys and Wright, 1965; McIntosh and Wardlaw, 1968; Mackintosh and McVittie, 1983).

Prominent clay seams halite

1030 m

sylvite

upper Patience Lake

5.1.2. Seismicity Natural dissolution of halite and mining of potash-rich beds have resulted in collapse-induced seismicity. These events, more than 40 since 1978, have been recorded across the northern and southern mining districts. The seismic events commonly record over 2.5 on the Richter scale. For example, a 3.8 magnitude event occurred at the Rocanville Mine in 1978. One of the largest pre-mining events recorded 5.5 in 1909. These seismic events may result in structural adjustments that permit communication with the overlying aquifers and establish pathways for brine seeps into the underground mine workings. Examples of mining operation induced fracturing of the overlying brittle Dawson Bay carbonate beds have been recorded (Gendzwill et al., 1982; Sepehr and Stimpson, 1988; Morgenstein and Sepehr, 1991).

1033 m halite

Roof Salt Marker Seams

1036 m

Production Horizon

sylvite

1039 m halite sylvite 1042 m halite

5.2. Interpretation of potash salt dissolution-collapse structures with the Alberta oil sands analogue

Intermediate Rock Salt

Models for the morphogenesis of the salt dissolution-collapse structures across the southern Saskatchewan area of the northern Williston Basin have been largely reliant on 3D seismic data and only limited reference well control. There is a substantive difference in the data base available for the oil sand area compared to the potash districts. The oil sand areas in northeast Alberta have innumerable wells with cored intervals and open pit mines. The Athabasca oil sands deposit and the potash mining areas are along the same regional salt dissolution trend (Fig. 2). The structural style resulting from salt dissolution-collapses can be observed along multi-km long cut faces of the open pit oil sands mines (Figs. 13B, 15). Moreover, these excavations into Lower Cretaceous bitumen-saturated strata have been guided by innumerable development wells with continuous cored intervals. Development wells for the oil sand mines number in the 10 s of thousands, often with 50–100 m well spacing. This obviates the necessity for widespread use of 3D seismic surveys for mine development, albeit seismic profiles are used for subsurface thermal recoveries (SAGD methodology). In contrast, there is a general lack of available cored intervals for the potash areas, but reliance on 3D seismic surveys to interpret salt dissolution-collapse related structures. The km-scale fault blocks exposed along cuts in the oil sand mines in northeast Alberta, and the well control into the Devonian substrate (Figs. 13B, 15), provide a useful structural analogue to interpret the morphogenesis implied by seismic images of the potash deposits (Broughton, 2013, 2015, 2016, 2017a,d). Development of salt dissolution-collapse structures in the oil sands vary from 10 s m diameter sinkholes to differential subsidence of multi-km scale fault blocks (Figs. 13B, 15). The effects of salt removal on the structural histories between the two areas are similar, although the potash area structures are more deeply buried and result in diffused structural configurations emanating up-section. Both the potash and the Athabasca oil sand areas were impacted by glacial meltwater flow that rejuvenated segments along the 1000 km long dissolution trend at the eastern margin of the Western Canada Sedimentary Basin. The glacial meltwater flows configured large 10 s km2 areas on the southern Saskatchewan topography (Broughton, 2017a), resulting in large scale collapses of adjoined fault blocks. Similar large scale collapses of linked fault blocks and sinkholes occurred across the Athabasca deposit area on the pre-Cretaceous and Cretaceous

1045 m

sylvite

lower Patience Lake

1048 m

1051 m

halite

Fig. 12. Patience Lake Member at the Allan Mine. A reference well at 05-22A34-01W3M illustrates the upper and lower Patience Lake ore zones and saltback intervals. Clay marker beds guide the top cut trajectory for the boring machines. Modified from Funk et al. (2018b).

(3) Late Pleistocene Floral, Battleford, and Haultain Formations of the Saskatoon Group. The initial collapse followed deposition of the Ardkenneth Member of the Cretaceous Bearpaw Formation, but prior to middle Pleistocene glaciation (pre-Illinoian). This was followed by dissolution-collapses during Late Wisconsinan glaciation, resulting in a 16 km long and 8 km wide structure with a 70 m relief superimposed on the pre-glacial collapse structure. The Patience Lake Mine is located along the northeast margin of this Low collapse structure (Fig. 14). As a result, the Dawson Bay seals overlying the potash beds were compromised along the fault-fractured margin of this collapse structure. Uncontrollable flooding of the underground workings forced permanent abandonment and conversion to a solution mine. 5.1. Minor salt removal issues 5.1.1. Leach zones Dissolution-collapse structures often have offset leach zones with low grade ore resulting from replacement of potassium salts by halite without disruption of the stratification (McIntosh and Wardlaw, 1968). The continuity of sylvite-rich ore zones can be disrupted by these irregular shaped leach zones, referred to as salt horses. These zones result 12

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Fig. 13. Salt dissolution collapse structural models developed from combining seismic imaging of the potash areas with geometrics of fault blocks exposed in the oil sand mines in northeast Alberta. (A) Seismic profile of a glacial meltwater reactivated collapse chimney located adjacent to the Lanigan Mine, and structural interpretation of the overlying strata collapse (Nemeth, 2002). (B) Application of the potash seismic imaging model to km-scale collapse structures exhumed by oil sand mines in northeast Alberta. Modified from Broughton (2017d).

of the southern Saskatchewan potash districts and beyond.

paleotopography (Cowie et al., 2015; Broughton, 2013, 2015, 2017d). Thus, glacial meltwater flows into the shallow subsurface of northeastern Alberta altered the groundwater chemistry but did not result in 10 s km2 regional Quaternary collapses (the Lows) comparable to those 13

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Fig. 15. Examples of differentially subsided fault blocks responding to multistaged removal of salt at depth exposed in oil sand mines of northeast Alberta (Fig. 13B). (A-B). Rotated fault blocks. (C) Suture-welded adjoined fault blocks. Modified from Broughton (2017d).

Fig. 14. Saskatoon Low collapse structure (m a.s.l.) on the Lea Park Formation, Upper Colorado Group. The Patience Lake Mine is located at northeastern margin of the collapse structure, resulting in uncontrollable seeps that flooded underground workings and necessitated conversion into a solution mine. Modified from Christiansen (1967) and Broughton (2018).

of control that can be exerted on the rate of gradual roof sag following excavation of the ore, with the objective of minimizing or preventing fracturing of the limestone bed seals up-section. Mines developed in the eastern Saskatchewan area favor long room and pillar extraction methodology because of the potentially more stable stratigraphic column, largely due to the lack of pervasive clay beds associated with the ore zones. This methodology also facilitates more efficient use of the boring machines with fewer corners and turns. In contrast, the stress relief mining methodology is more commonly used by mines to the west, such as those near the city of Saskatoon, because of the increased prevalence of clay beds.

6. Mining methodology Conventional underground potash mines of southern Saskatchewan target sylvinite ore zones at 1000–1200 m depths. At a regional scale, these ore zones consist of beds that are tabular, flat lying and have consistent thickness. These characteristics facilitate development of large horizontal underground excavation patterns, but are also favorable for horizontal well arrays for solution mining. Underground operations use either long room and pillar or stress relief mining methods, or both (Jones and Prugger, 1982). Extraction rates are maintained at less than 40%, although some localized areas of a mine may approach 50% (Pauls, 2017), to limit or constrain sagfracturing of the overlying 30–40 m thick limestone beds of the Dawson Bay Formation. Maintaining integrity of this overlying carbonate interval is important as a top seal or barrier to preclude descent of overlying aquifer waters associated with the Cretaceous strata, and thereby prevent brine seeps into the mine workings. The methodology utilized is determined by depth to the ore zone and thickness of the interval between the ore zone and the overlying Dawson Bay Formation. The relative abundance of clay beds (Fig. 12) within and adjacent to the ore zone partially controls the distribution of rock deformation stresses (Pauls, 2017). A salt-back thickness of at least 9 m is generally accepted as necessary to ensure a safe and stable roof for mining activity. Potash ore zones deeper than 1000 m result in stresses close to the maximum uniaxial compressive strength of the potash beds, ~25 MPa. Yield begins at about 11 MPa, triggering creep-flow and closure of the voids created by removal of ore (Duncan and Lajtai, 1993; Pauls, 2017). Creep-flow closure rates for potash mines are about of 2–3 cm per 100 days (Pauls, 2017). These factors determine the degree

6.1. Underground mining Long Room and Pillar Mining. This methodology utilizes a design with an array of equally spaced rooms interconnected by access passageways. A km-scale block of ore is delineated by 4 or 5 development entries and then mined by linear cuts between ends. Parallel excavation cuts are made on each mining room with pillars of by-passed ore to ensure roof stability. The ore zone is sequentially dissected by successive passes to cut out these elongated rooms or panels. The panel rooms are typically 18 m wide before a pillar is created to achieve 35–40% extraction rate (Pauls, 2017). Long-term stability is responsive to creep flow along the mining room walls, and varies with the dimensions of the pillars. This is enhanced by increasing pillar length or width. Early mine design used square pillars, but elongated pillar designs evolved to ensure greater productivity while controlling the increased load capacity for the weight of overlying strata. This constrains the depth of minable potash ore by this methodology. Room and pillar mining necessarily requires distribution of stresses into the abutment pillars to 14

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horizontally drilled wells from a surface pad, such as those now commonplace for exploitation of oil shale reservoirs (Halabura and Hardy, 2007). Early potash solution mining with the use of vertical wells was initially employed at the Belle Plaine Mine (Fig. 1) (Garrett, 1995; Fourie and Hambley, 2018). Although many technical aspects remain proprietary, a generalized methodology consists of: Stage 1. Injection of ambient fresh water creates a sump area at the level of the halite floor underlying the ore zone. This results in a basal horizon for the solution cavern to accommodate the produced insoluble residues. The injected water dissolves both the NaCl and KCl, creating a solution cavern between the injector and recovery wells which are usually spaced 70–80 m apart. Following the development of a cavernous horizon at the base of the ore zone, the up-hole casing of the injection well is perforated for injection of heated fresh water to stimulate vertical chamber growth. Stage 2. Any halite-dominated non-ore interval is isolated from the cavity building process by a bridge plug set in the casing, such as below the base of the Belle Plaine Member ore interval and the casing is severed. A hydraulic fracturing process is then employed between the injector and producer wells along the clay seam at the base of the Belle Plaine Member. Stage 3. Conversion of the expanding solution cavern into a production cavern follows with injection of heated brine saturated with NaCl, a process often referred to as secondary mining. This results in selective dissolution of the KCl preferentially over NaCl from the collapsed wall rock rubble. Precipitation of halite occurs and insoluble residues settle to the bottom of the chamber. Various techniques are employed to maintain horizontal cavern development by slowing the injection-production flow to allow for more efficient and complete saturation of the KCl. Oil can be injected into the brine in the solution cavern, resulting in a surface film to enhance horizontal expansion of the chamber and constrain rate of vertical growth. Replacement of the chamber brine may also occur.

preclude fracturing in the overlying strata. Stress Relief Mining. This methodology employs horizontally adjoined V-shaped rooms having a chevron or herringbone configuration. Entries, 4–5 in number, are arrayed to converge on a single centrally located development heading. Stress relief mines have rooms that are typically 10–12 m wide, compared to the 18 m widths of long room mines. Vertical stresses in the pillars are shifted to the barrier pillars, permitting the outer production rooms to sag and collapse after removal of the ore. This transfers stress to the outer abutments, thereby reducing stress in the middle of the room-pillar configuration along the central development headings. Horizontal stresses act upon the salt-back roofbeam interval across the mine back, which are thinner than pillars and more prone to failure. Buckling of a room floor and overlying salt-back due to horizontal stresses is less likely compared to long room and pillar extraction, as the stresses concentrate along the top and bottom corners of the outside rooms. This results in creep/fracture of the salt-back and transfer of stress from the middle of the mining area to more competent limestone beds overlying the excavated ore voids (Pauls, 2017). Stress relief mining is adaptable for ore removal zones that have increased structural instability and enables greater mining depth compared to long room and pillar operations. 6.2. Solution mining Solution mining methodology is employed at several operations where the depth of the ore zone precludes underground dry mining. It also has been employed as remedial action upon flooding of an underground dry mine. The standard operational procedure is to inject and circulate fresh water to dissolve salts in the ore zone (Husband and Ozsahin, 1967a,b). Fig. 16 illustrates the relative solubility curves for KCl and NaCl. Injection of NaCl brine heated above 70 °C preferentially dissolves KCl in the chamber wall rock, which remains in solution as the NaCl in the brine becomes super-saturated and precipitates to the chamber floor. The KCl-saturated brine is pumped to surface. Operational procedures at active solution mines in Saskatchewan, such as the size and array of solution caverns and their rates of grown, are considered proprietary information. Publically available data are largely from development proposals. Two types of solution injections have been described: (1) vertical injector and production wells in communication, and (2) horizontal wells deployed from surface pads with multiple injector and production boreholes in parallel or fanshaped arrays. Most early solution mining in the 1960s and 1970s employed only vertical well designs. However, major advances in drilling technology resulted in designs with arrays of multiple

7. Mining districts Most of the eight conventional underground mines and three solution mines in Saskatchewan date to the 1960s and 1970s (Potash Corporation, 2016) (Fig. 1). The Bethune solution mine of K + S Potash Canada, located west of Regina, is the newest mine to be commissioned with production initiated in 2017. The mines are distributed across southern Saskatchewan along two west-to-east trending districts (Figs. 1, 9–11). The northern district has conventional underground Fig. 16. Relative solubility curves for halite and sylvite. NaCl saturated brine heated above 70 °C. When injected into a solution mine chamber, the brine preferentially dissolves KCl from wall rock. This causes NaCl supersaturation and precipitation of crystalline halite to the chamber floor. Modified from Soroka and Lahonen (2018).

15

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Table 1), produces from the Patience Lake Member at a depth of 1020 m. It is currently operated by Nutrien Ltd. Regional stratigraphic maps indicate that the Patience Lake Member is 25–28 m thick in the area of the mine (Fig. 11, map loc. 3). The Belle Plaine Member has only a 4–7 m thickness (Fig. 10, map loc.3), whereas the Esterhazy Member was not developed (Fig. 9, map loc. 3) (Yang et al., 2018a,b,c). The original underground operations used long room and square pillar methodology. There are more than 600 km of workings covering an equivalent surface area of 50 km2 (Smith, 1988; Soroka and Lahonen, 2018). Early underground mining operations were frequently disrupted by multiple brine ingresses. After only a year of production, operations were halted because of significant seeps into the shaft. Six years of remedial grouting efforts followed, and production resumed in 1965. However, a new series of water ingress events started in 1975. A boring machine operating adjacent to the southern edge of the lease made contact with the overlying Second Red Bed. This resulted in a small brine leak, but after a few days the shale roof collapsed. Within a few weeks, brine flow into the underground workings was recorded at 900 L/minute. Grout injections into offset drill holes and construction of bulkheads that temporarily reduced the flow to only 40 L/minute were ultimately unsuccessful. Rapidly increasing brine flow into the underground workings reached 18,000 L/minute by 1986, and subsequently 45,000 L/minute by February 1987. Underground operations ceased and the mine was completely flooded by July 1987. The uncontrollable flooding resulted in abandonment of the underground operation and the workings were converted into a solution mine. Seismic surveys have determined that mining-induced fractures resulted in connectivity to nearby brine-filled chimneys associated with a regional-scale salt dissolution-collapse structure known as the Saskatoon Low (Fig. 14). This salt dissolution-collapse structure and associated faults are aligned along the southern and western margins of the mine (Gendzwill and Martin, 1996; Broughton, 2017c, 2018). This major salt dissolution-collapse structure developed along the regional dissolution trend at the eastern margin of the Williston Basin (Fig. 2).

mines located from about 20 km west of the city of Saskatoon eastward towards the provincial boundary with Manitoba. Depths to the Esterhazy and Patience Lake ore intervals are 1000–1100 m along this northern trend. The southern mining district is a trend with a cluster of mines located west and east of Regina, continuing eastward to a cluster of mines located along the provincial boundary with Manitoba. Mines of the southern district near Regina target Belle Plaine Member ore, but the increased depth to 1500–1600 m necessitates use of solution mining technology. In contrast, the southern district mines near the provincial boundary with Manitoba, such as the K1 and K2 underground mines, target the Esterhazy Member ore. 7.1. Mines of the northern (Saskatoon) district The northern district consists of mine sites trending eastward from the vicinity of Saskatoon. These are, west to east: Vanscoy, Cory, Patience Lake, Allan, Colonsay (suspended) and Lanigan Mines (Fig. 1, Table 1). The operations are underground dry mines, except for the Patience Lake Mine which was originally build as an underground operation but subsequently converted to a solution mine because of uncontrollable flooding. 7.1.1. Vanscoy Mine The mine is currently operated by Nutrien Ltd., and is located 30 km southwest of the city of Saskatoon (Fig. 1, Table 1). The operation recovers ore from the Patience Lake Member at depths of 1000–1130 m (Stoner and Mackintosh, 2011; Bartsch et al., 2014). The ore is recovered mostly from the upper and lower Patience Lake Member, but also from the Belle Plaine Member (Fig. 10, map loc. 1). Regional maps indicate the Patience Lake Member is 19–22 m thick across the mine area (Fig. 11, map loc. 1). In contrast, the Belle Plaine Member is only 3 m thick (Yang et al., 2009a,b,c,d, Yang et al., 2018a,b,c). The Esterhazy Member is poorly developed across the mine area (Fig. 9, map loc. 1), and occurs only as a stratigraphic marker. A major incident occurred in 1970 when a routine shaft grouting procedure breached an aquifer, resulting in rapid influx of water at a rate of 65,000 L/minute. The mine was flooded within 5 days, forcing closure for two years. Production resumed in 1972 after grouting and dewatering. A roof failure in 1985 occurred at the end of an abandoned mining panel, resulting in collapse of 4 m thick section of overlying Red Bed shale and 3 m of limestone. A decade long program of drilling and grouting operations attempted to control the brine seeps emanating from fractured wall rock along the western boundary of the mine. Flows were recorded up to 225 L/minute along a 550 m wide section (Mackintosh and McClung, 2000).

7.1.4. Allan Mine This underground operation, located 45 km southeast of Saskatoon (Fig. 1, Table 1), is operated by Nutrien Ltd. Mining operations use stress relief methodology to excavate ore from the upper Patience Lake at a depth of 1000 m (Gebhardt, 1993; Funk et al., 2018b). The upper Patience Lake ore zone is approximately 3.35 m thick. The lower Patience Lake is not mined at present. Regional maps indicate the Patience Lake Member is 18–19 m thick, Belle Plaine Member 10–13 m thick across the mine site, but the Esterhazy Member has zero thickness (Figs. 9–11, map loc. 4) (Yang et al., 2018a,b,c). The Belle Plaine Member has appreciable thickness but low KCl grade. The well located at 05-22A-34-01W3M illustrates a representative Patience Lake ore zone stratigraphy for this mine area (Fig. 12). Brine ingress into the underground mine workings has been negligible to minor since production began in 1968, except for a significant breach event that occurred at approximately 570 m depth during shaft sinking. A wall section of the shaft failed and the incomplete shaft was flooded (Prugger and Prugger, 1991; Funk et al., 2018b). A concrete plug was installed at the bottom of the water-filled shaft, and the breach was successfully sealed. In the 1990s, the concrete liner of a production shaft at 671–750 m depth was replaced because of minor brine seepage. A minor influx of brine also occurred in 1996 at a flow rate of 20 L/ minute, but eventually ceased. Current seepage into the service shaft is at a rate of 25 L/minute and 145 L/minute into the production shaft (Funk et al., 2018b). These flows are considered negligible and do not interfere with mine operations.

7.1.2. Cory Mine The underground Cory Mine, 16 km southwest of the city of Saskatoon (Fig. 1, Table 1), is operated by Nutrien Ltd. The operations remove ore from the upper Patience Lake Member at 980–1045 m depth (Fig. 7). Regional maps of the Patience Lake Member indicate a 16–18 m thick interval across the mine area (Fig. 11, map loc. 2), in contrast to a thinned Belle Plaine Member (< 3 m) (Fig. 10, map loc. 2) and zero thickness for the Esterhazy Member (Fig. 8, map loc. 2) (Yang et al., 2018a,b,c). Only minor seepages of brines into the underground workings have occurred during the history of this mining operation. Seeps are estimated at only 40–200 L/minute. The brine is collected and pumped to surface for disposal in the tailings. Mining induced seismic events have occurred intermittently. For example, six events were recorded during the 1979–1983 period with body wave magnitudes of 2.3–3.0 (Gendzwill et al., 1982; Gendzwill, 1984; Prugger, 1985; Gendzwill and Prugger, 1988).

7.1.5. Colonsay Mine This underground mine operation of the Mosaic Company has an annual capacity of 2.6 Mt but had been operating at half capacity

7.1.3. Patience Lake Mine This solution mine, located 18 km east of Saskatoon (Fig. 1, 16

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meter thick (Figs. 10 and 11, map loc. 9). Long room and pillar mining is used. A major brine influx event occurred in 1984 when one of the mining rooms came in contact with a brine-filled chimney. Uncontrollable brine flow into the mine was as high as 19,000 L/minute. Because of the flooding, all mining operations were suspended until early 1985, when a concrete plug with high pressure valves was installed at the wall breach point, resulted in successful containment (Prugger and Prugger, 1991).

because of current economic conditions (Fig. 1, Table 1). Mine production has been suspended in 2019. Ore was recovered from the Patience Lake Member at depth of 1020 m. Operational procedures are deemed proprietary. 7.1.6. Lanigan Mine This underground mine operation of Nutrien Ltd. is located 100 km east of Saskatoon (Fig. 1, Table 1). Ore is extracted from both the upper and lower Patience Lake Member at 940–1030 m depths. Ore removal in the upper Patience Lake uses stress relief mining methodology, whereas long room and pillar extraction is used for the lower Patience Lake interval (Gebhardt, 1993). Although ore is recovered from both of these zones, the operational procedure is to mine only one zone at a time to limit the potential impact of structural subsidence up-section and to prevent compromising the overlying carbonate seal (Funk et al., 2018c). The stratigraphic thickness of the Patience Lake Member is 16–19 m (Fig. 11, map loc. 6), whereas a 10–13 m thickness is indicated for the Belle Plaine Member (Fig. 9, map loc. 6), and zero for the Esterhazy Member (Fig. 8, map loc. 6) (Yang et al., 2018a,b,c). The ore interval averages 3.7 m thick in the upper Patience Lake and 4.9 m thick in the lower Patience Lake. Although the Belle Plaine Member has appreciable thickness, the grade is low and not economic. Carnallite concentration may be significant in the basal interval of the lower Patience Lake ore zone. There have been numerous but minor brine seeps into the underground workings, but none have impacted mining operations. For example, a new seep occurred in 2012, recorded at 170 L/minute. The flow is ongoing, but contained.

7.2.4. Bethune Mine This solution mine is operated by K + S Potash Canada at a location west of Regina (Fig. 1, Table 1). Initial commercial production was achieved in 2017. The mine consists of 36 production caverns developed within the Esterhazy Member at 1500 m depth. Regional maps of the Prairie Evaporite Members indicate a 13–16 m thickness for the Patience Lake Member (Fig. 11, map loc. 11), compared to 7–8 m for the Belle Plaine Member (Fig. 10, map loc. 11) and 10–13 m for the Esterhazy Member (Fig. 9, map loc. 11) (Yang et al., 2018a,b,c).

7.2. Mines of the southern (Regina) district

8. Developing mines and projects

The southern district consists of solution mines to the southwest and underground operations to the southeast (Fig. 1, Table 1). The solution mines are Bethune and Belle Plaine. The underground mines are Rocanville and Esterhazy K1 and K2.

New mines currently under construction and major proposed development projects include both underground and solution operations (Fig. 1). Descriptions are presented for some of the more important projects, many of which have been suspended in recent years because of unfavorable potash markets.

7.2.3. Belle Plaine Mine This solution mine, operated by the Mosaic Company, is located 45 km west of Regina (Fig. 1, Table 1). Ore is recovered from the Belle Plaine Member at 1600 m depth (Worsley and Fuzesy, 1979; Fuzesy, 1982). Regional stratigraphic maps indicate a thickness of 9–16 m for the Patience Lake Member (Fig. 11, map loc. 10), 4–7 m or more thickness for the Belle Plaine Member (Fig. 10, map loc.10), and 7–10 m for the Esterhazy Member (Fig. 9, map loc. 10) in the vicinity of the solution mining operation (Yang et al., 2018a,b,c).

7.2.1. Esterhazy K1 and K2 Mines The underground K1 and K2 Mines of the Mosaic Company are located near the provincial boundary with Manitoba at the town of Esterhazy (Fig. 1, Table 1). The surface print of the K1-3 Mines is 30 km long and 15 km wide (Mosaic Corporation, 2016). The K1 and K2 Mines interconnect underground. The mines use conventional room and pillar mining methodology to recover ore from the Esterhazy Member. Regional thickness maps across the K1 and K2 (and K3) mine area indicate 7–10 m thickness for the Esterhazy Member (Fig. 9, map loc. 7, 8), and 4–7 m thickness for the Belle Plaine Member (Fig. 10, map loc. 7, 8). The Patience Lake Member has zero thickness (Fig. 11, map loc. 7, 8). Operational details are deemed proprietary. Brine influxes and seismic events since the mid-1980s have periodically impacted the K1-K2 operations. A more recent influx occurred during January 2007, recording a flow of 76,000 to 95,000 L/minute. These persistent brine ingress events has favored development of the K3 Mine as an eventual replacement of the K1 and K2 operations. In July 1987, a brine influx occurred during a salt dissolution collapse event, resulting in an earthquake recorded at 2.7 on the Richter scale. Three shocks also occurred in 1981 with recorded magnitudes of 2.9, 2.7, and 3.2. These seismic events have been interpreted as Mohr-Coulmb type failures (Gendzwill, 1984).

8.1. Burr project An underground mine was originally proposed by BHP approximately 107 km east of Saskatoon (Fig. 1) (Lomas, 2018). The development is now suspended. Anticipated annual production would have been 2 Mt from the Patience Lake Member. The average thickness of the upper ore zone is 3.4 m. The lower zone averages 4.6 m thick. 8.2. BHP Jansen Mine/project The development site is 140 km east of Saskatoon (Halabura et al., 2005) (Fig. 1). This proposed underground mine by BHP would use long room and pillar methodology to initially produce 4 Mt of ore annually by 2023. Development of the Jansen project continues, but a production decision has not been made. It is designed to eventually achieve an annual peak capacity of 24 Mt of ore, resulting in 8 Mt of finished product (BHP, 2018). Production and service shafts to the depths of 1000 m were completed in 2018. 8.3. Wynyard project This solution mining project of Karnalyte Resources is located 175 km east of Saskatoon (Fig. 1). The project is unusual because it specifically targets a 9–10 m thick carnallite-rich bed of the Patience Lake Member that occurs at 910–1010 m depth. The ore is greater than 40% carnallite, in contrast to carnallite-rich beds that are avoided by mining operations elsewhere. The 15 m thick Belle Plaine Member is also carnallite-rich at 927–1030 m depth. In contrast, the Esterhazy

7.2.2. Rocanville Mine The underground mine, 200 km east of Regina (Fig. 1, Table 1), is operated by Nutrien Ltd. Shafts to the Esterhazy Member ore zone have depths of 895–1040 m (Funk et al., 2018d). Regional maps indicate that the Esterhazy Member is 4–8 m thick (Fig. 9, map loc. 9) (Yang et al., 2018a,b,c). Patience Lake and Belle Plaine members are each less than a 17

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30% of the world production from 8 underground and 3 solution mines. Annual production (2018) is currently 23 Mt of KCl processed from an ore consisting of halite and sylvite with minor carnallite and insoluble clay residues.

Member occurs as a 17 m thick sylvite-rich interval at 970–1074 m depth (Rauche et al., 2016). Brine is proposed to be injected into the carnallite-rich zones of the Belle Plaine and Patience Lake Members, resulting in parallel solution caverns at 915–980 m depths. Cavern development would also occur in the carnallite-poor but sylvite-rich Esterhazy Member as a secondary target. This mine design would inject production brines to hot leach the carnallite-rich zones and cold leach the sylvite-rich zones.

1. Potassium chloride-rich brines accumulated during the late stage evaporation cycle that was geographically constrained to the southern Saskatchewan sub-basin area of the northern Williston Basin. Several potash-rich beds accumulated as the uppermost 60 m thick interval of the Prairie Evaporite Formation. In contrast, halitedominated beds accumulated elsewhere in the Middle Devonian salt basin that extends across western Canada and into adjacent areas of Montana and North Dakota. The sylvite-rich beds formed largely as primary deposits in combination with diagenetic processes that leached magnesium chloride from carnallite-rich beds and transitioned to sylvite. As a result, sylvite beds resulting from diagenetic alteration of carnallite-rich beds dominate the uppermost interval of the Prairie Evaporite Formation. This is the reverse of normal mineral sequencing associated with sea water evaporation. These diagenetic processes were multi-staged and vary from early shallow burial to subsequent deeper burial episodes that altered the carnallite during groundwater circulations associated with several Phanerozoic basin deformations. 2. The southern Saskatchewan potash mines are distributed as two major mining districts, the northern (Saskatoon) trend and the southern (Regina) trend. The northern mines are mostly underground operations at approximately 1000 m depths located in the vicinity of Saskatoon and eastward toward the provincial boundary with Manitoba. The southern mining district consists of solution mines located in the vicinity of Regina that exploit ore at depths of 1500–1600 m, and shallower ore zones permitting underground mining to the east near the provincial boundary with Manitoba. 3. The depth of the several potash-rich members of the Prairie Evaporite Formation and the abundance of clay beds within the ore zone determine the mining methodology used to exploit the resource: (1) long room and pillar versus stress relief operational methods for underground mines; (2) solution mining for more deeply buried ores. 4. Brine seeps into the underground operations have variously impacted most underground mining operations. These seepages resulted from the combination of salt dissolution at depth impacting structural integrity of the overlying strata, and the influx of glacial meltwater into the subsurface and come in contact with the salt beds below the underground mines. The sealing integrity of the Dawson Bay Formation carbonate beds from overlying Cretaceous aquifers was sometimes compromised. Historically, these seepage events have been largely controlled by grouting and the long term impact on mining operations being largely negligible. However, some significant seepage events resulted in closure of several mining operations for months or up to 1–2 years. A catastrophic mine flooding event necessitated conversion of one underground operation into a solution mine.

8.4. Vanguard one project This potential solution mine has been proposed by Gensource Potash Corporation at a site 170 km south of Saskatoon and 150 km northwest of Regina (Fig. 1). The project was planned to commence operation by 2020 with annual KCl production of 250,000 tonnes from the lower Patience Lake Member. 8.5. Kronau project This solution mining project is located 13 km southeast of Regina (Fig. 1). The project was at the feasibility stage when Vale SA, the Brazilian operator, suspended work in 2015 because of the economic conditions (Golder Associates, 2011). Prior to suspension of development, annual production of 2.9–3.3 Mt from 1650 m depth was scheduled for 2020. Mosaic obtained control of the project in 2017 with the acquisition of the fertilizer properties of Vale SA. 8.6. Milestone project This solution mine development by Western Potash was proposed for a site 35 km southeast of Regina (Hambley et al., 2015) (Fig. 1). The operation would target the Esterhazy Member where the ore interval is 5.7 m thick and has an average grade of 20.9% K2O. The Patience Lake Member, 10.5 m thick, has an average grade of 18% K2O with 11% insoluble residues. The Belle Plaine Member averages a thickness of 4.4 m and average grade of 18.5% K2O with 4% insoluble residues. Some areas of the Esterhazy Member have carnallite-rich areas that exceed the 6% cutoff. The carnallite grade is significantly less than the threshold limit of 6% in ores of the Patience Lake and Belle Plaine Members and for specific areas of the Esterhazy Member (Hardy et al., 2011). 8.7. K3 mine/project The K3 underground mine is under construction by Mosaic with completed shafts (Mosaic Corporation, 2016, 2017; BHP, 2018). It is located to the west of the K2 Mine (Fig. 1). The K3 Mine will not be at full operational capacity until 2024 following initial production of 400,000 tonnes in 2019. The mine will replace the flood-prone K1-2 Mines when at full capacity. It is anticipated to initially produce 3 Mt of ore annually, resulting in 1 Mt of finished product. The K3 Mine at full capacity is anticipated to produce as much as 19 Mt of ore annually (Mosaic Corporation, 2016). The K1-2–3 mining complex uses conventional room and pillar mining methodology to mine ore from the Esterhazy Member. Regional maps of the potash members across the K1-K2-K3 mining complex indicate a 7–10 m thickness for the Esterhazy Member (Fig. 9, map loc. 7, 8), and 4–7 m thickness for the Belle Plaine Member (Fig. 10, map loc. 7, 8). The Patience Lake Member has zero thickness (Fig. 11, map loc. 7, 8). The K3 Mine is designed to access the surface processing facilities of the K2 Mine, which are being expanded for this purpose.

Acknowledgements The author appreciates the contribution of illustrations of mines operated by Nutrien Ltd., and the cooperation of Mr. Craig Funk, Director, Earth Science, Nutrien Ltd. The cooperation of the staff of the Saskatchewan Geological Survey is greatly appreciated for providing maps of the potash-rich members, including the data for Table 1. The contribution by Dr. C. Yang was especially noteworthy. Prof. N. Wardlaw, University of Calgary, provided useful commentary on sections regarding sylvite-carnallite relationships. Technical review of the manuscript and useful commentaries on the mine geology was provided by Nutrien Ltd. staff. The author appreciates the commentary of Dr. Balazs Nemeth, BHP Canada, and several anonymous reviewers of

9. Conclusions The potash reserves of southern Saskatchewan area are one of the most important known economic deposits, resulting in approximately 18

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earlier manuscript versions, resulting in a greatly improved paper. Preparation of this paper has not received external funding. There are no conflicts of interest.

Spangler, L. (Eds.), Proceedings, U.S. Geological Survey, Karst Interest Group, San Antonio, Texas, May 16-18, 2017. U.S. Geological Survey, Scientific Investigations Report 2017-5023, 92-106. Broughton, P.L., 2018. Orogeny and collapse of the Devonian Prairie Evaporite karst in Western Canada: Impact on the overlying Cretaceous Athabasca Oil Sands. In: Parise, M., Gabrovsek, F., Kaufmann, G., Ravbar, N. (Eds.), Advances in Karst Research: Theory, Fieldwork and Applications. Geological Society London, Special Publication 466, 25-78. Brown, D., Brown, D., 1987. Wrench-style deformation and paleostructural influence on sedimentation in and around a cratonic basin. In: Longman, M. (Ed.), Williston Basin – Anatomy of a Cratonic Oil Province. Rocky Mountain Association of Geologists, Denver, pp. 57–70. Chairawiwut, W., 2015. Chloride salts removal by non-planted constructed wetlands receiving synthetic brines from Belle Plaine potash mining. M.Sc Thesis. University of Regina, Regina, Saskatchewan, pp. 91. Chipley, D., 1995. Fluid History of the Saskatchewan Sub-basin of the Western Canada Sedimentary Basin: Evidence from the Geochemistry of Evaporites. Ph.D. thesis. University of Saskatchewan, Saskatoon, Saskatchewan, pp. 289. Chipley, D., Kyser, T., 1991. Large scale fluid movement in the Western Canadian Sedimentary Basin as recorded by fluid inclusions in evaporites. In: Christopher, J., Haidl, F. (Eds.), Sixth International Williston Basin Symposium. Saskatchewan Geological Society, Special Publication 11, Regina, Saskatchewan, 265-269. Chipley, D., Kyser, T., 1989. Fluid inclusion evidences for the deposition and diagenesis of the Patience Lake Member of the Devonian Prairie Evaporite Formation, Saskatchewan, Canada. Sed. Geol. 64, 287–295. Christiansen, E., 1967. Collapse structures near Saskatoon, Saskatchewan. Can. J. Earth Sci. 4, 757–767. Christiansen, E., Sauer, E., 2002. Stratigraphy and structure of Pleistocene collapse in the Regina Low, Saskatchewan, Canada. Can. J. Earth Sci. 39, 1411–1423. Corporation, Potash, 2016. Form 10-K; 2016 Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. Potash Corporation of Saskatchewan, Saskatoon, Saskatchewan, pp. 33. Cowie, B., James, B., Mayer, B., 2015. Distribution of total dissolved solids in McMurray Formation water in the Athabasca Oil Sands Region, Alberta, Canada: Implications for regional hydrogeology and resource development. AAPG Bull. 99, 77–90. Delaney, G., 2017. Saskatchewan’s Mineral Sector Winter 2017/18: Status, Outlook and Opportunities. Presentation, Saskatchewan Geological Survey 2017 Open House, Regina, pp. 29. DeMille, G., Shouldice, J., Nelson, H., 1964. Collapse structures related to evaporites of the Prairie Formation, Saskatchewan. Geol. Soc. Am. Bull. 75, 307–316. Duncan, E., Lajtai, E., 1993. The creep of potash salt rocks from Saskatchewan. Geotech. Geol. Eng. 11, 159–184. Dunn, C., 1976. Saskatchewan potash in 1975 - an update on our knowledge. In: Proceedings, 11th Forum on Geology of Industrial Minerals, 18-20 June 1975, Kalispell, Montana. Montana Bureau of Mines and Geology, Special Publication 74, Butte, Montana. Dunn, C., 1982. Geology of the Middle Devonian Dawson Bay Formation in the Saskatoon Potash Mining District, Saskatchewan. Saskatchewan Geological Survey, Report 194, Regina, Saskatchewan, pp. 117. Eccles, D.R., Al-Souqi, M., Grattan, K., Dufresne, M.B., 2009. Preliminary Investigation of Potash Potential in Alberta. Alberta Geological Survey, Open File Report 2009-20, Edmonton, Alberta, pp. 29. Ford, D., 1997. Principal features of evaporite karst in Canada. Carbonates Evaporites 12, 15–23. Fourie, L., Hambley, D.F., 2018. Technical Report NI 43–101 Summarizing the Feasibility Study for the Vanguard One Potash Project, Saskatchewan, Revised February 23, 2018. Agapito Assoc., Engcomp Eng., for Gensource Potash Corporation, Saskatoon, Saskatchewan, Terra Modelling Services, pp. 167. Funk, C., Derkach, J., MacKenzie, L., 2018a. Technical Report on Cory Potash Deposit (KL103B), Saskatchewan, Cory Potash National Instrument 43–101. Nutrien Ltd., Saskatoon, Saskatchewan, pp. 70. Funk, C., Derkach, J., MacKenzie, L., 2018c. Technical Report on Lanigan Potash Deposit (KLSA001C), Saskatchewan, Lanigan Potash National Instrument 43–101. Nutrien Ltd., Saskatoon, Saskatchewan, pp. 79. Funk, C., Derkach, J., MacKenzie, L., 2018b. Technical Report on Allan Potash Deposit (KL112RA), Saskatchewan, Allan Potash National Instrument 43–101. Nutrien Ltd., Saskatoon, Saskatchewan, pp. 72. Funk, C., Derkach, J., MacKenzie, L., 2018d. Technical Report on Rocanville Potash Deposit (KL305), Saskatchewan, Rocanville Potash National Instrument 43-101. Nutrien Ltd., Saskatoon, Saskatchewan, pp. 78. Fuzesy, A., 1982. Potash in Saskatchewan. Saskatchewan Geological Survey, Report 181, Regina, Saskatchewan, pp. 44. Fuzesy, A., 1984. Potash in western Canada. In: Guillet, G.R., Martin, W. (Eds.), Geology of Industrial Minerals in Canada. Canadian Institute of Mining and Metallurgy, Special Volume 29, Westmount, Quebec, 188-194. Garrett, D.E., 1995. Potash: Deposits, Processing, Properties and Uses. Springer, Netherlands, pp. 744. Garven, G.A., 1989. Hydrogeological model for the formation of the giant oil sands deposits of the Western Canada Sedimentary Basin. Am. J. Sci. 289, 105–166. Garven, G., Freeze, R., 1984. Theoretical analysis of the role of groundwater flow in the genesis of stratabound ore deposits, 2, Quantitative results. Am. J. Sci. 284, 1125–1174. Gebhardt, E., 1993. Mine planning and design integration. Can. Inst. Min. Metall. Bull. 86, 41–49. Gendzwill, D.J., 1984. Induced seismicity in Saskatchewan potash mines. In: Gay, N., Wainwright, E. (Eds.), 1982 Proceedings, First International Congress on Rockbursts

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.oregeorev.2019.103117. References Anderson, N., Hinds, R., 1997. Glacial loading and unloading: a possible cause of rock salt dissolution in the Western Canada Basin. Carbonates Evaporites 12, 43–52. Anderson, N., Knapp, R., 1993. An overview of some of the large scale mechanisms of salt dissolution in western Canada. Geophysics 58, 1375–1387. Bąbel, M., Schreiber, B.C., 2014. Geochemistry of evaporites and evolution of seawater. In: Treatise on Geochemistry, second ed. Elsevier, pp. 484–560. Bachu, S., 1995. Synthesis and model of formation-water flow, Alberta basin, Canada. AAPG Bull. 79, 1159–1178. Bachu, S., 1999. Flow systems in the Alberta basin: patterns, types and driving mechanisms. Bull. Can. Pet. Geol. 47, 455–474. Bachu, S., Underschultz, J., Hitchon, B., Cotterill, D., 1993. Regional-scale Subsurface Hydrogeology in Northeast Alberta. Alberta Geological Survey, Bulletin 61, Edmonton, Alberta, pp. 44. Bachu, S., Underschultz, J., 1993. Hydrogeology of formation waters, northeastern Alberta. AAPG Bull. 77, 1745–1768. Bamburak, J.D., Nicolas, M., 2009. Revisions of the Cretaceous stratigraphic nomenclature of southwest Manitoba (parts of NTS 62F, G, H, J, K, N, O, 63 C, F). In: 2009 Report of Activities, Manitoba Geological Survey, pp. 183–192. Bannatyne, B., 1983. Devonian Potash Deposits in Manitoba. Manitoba Geological Survey, Open File Report OF83-3: Winnipeg, Manitoba, pp. 27. Bartsch, M., Grimm, D., Mackintosh, A.D., 2014. Technical Report on Vanscoy Potash Operations, Vanscoy, Saskatchewan. Vanscoy National Instrument 43-101. Agrium, Saskatoon, pp. 89. Bebout, D., Maiklem, W., 1973. Ancient anhydrite facies and environments, Middle Devonian Elk Point Basin, Alberta. Bulletin of Canadian Petroleum Geology 21, pp. 287–243. Berenyi, J., Yang, C., Jensen, G., 2008. Potash in Saskatchewan: an overview of exploration and developments. Saskatchewan Geological Survey, Open House Abstracts, Regina, Saskatchewan, pp. 30. Betcher, R., Grove, G., Pupp, C., 1995. Groundwater in Manitoba: Hydrogeology, Quality concerns, and Management. National Hydrology Research Institute, Contribution CS93017, Saskatoon, Saskatchewan, pp. 47. Bezys, R., Kreis, K., Martiniuk, C., Barchyn, D., Christopher, J., Coolican, J., Conley, G., Costa, A., Haidl, F., Keller, G., Kent, D., Marsh, A., Matile, G.L.D., Nicolas, M.P.B., Thomas, P., Spooner, S., Yurkowski, M., Nimegeers, A., Nickel, E., Opseth, M., Music, T., 2008b. Devonian Prairie Evaporite Structure Contour, Stratigraphic Map SM2008DPE-S. Manitoba Geological Survey, Winnipeg, Manitoba. Bezys, R., Kreis, K., Martiniuk, C., Barchyn, D., Christopher, J., Coolican, J., Conley, G., Costa, A., Haidl, F., Keller, G., Kent, D., Marsh, A., Matile, G.L.D., Nicolas, M.P.B., Thomas, P., Spooner, S., Yurkowski, M., Nimegeers, A., Nickel, E., Opseth, M., Music, T., 2008a. Devonian Prairie Evaporite Isopach, Stratigraphic Map SM2008-DPE-I. Manitoba Geological Survey, Winnipeg, Manitoba. BHP, 2018. BHP Annual Report 2018, pp. 297. Broughton, P.L., 1977. Origin of coal basins by salt solution tectonics in western Canada. Ph.D. Thesis. Univ. Cambridge, pp. 288. Broughton, P.L., 1985. Geology and resources of the Saskatchewan coalfields. In: Patching, T. (Ed.), Coal in Canada. Special Volume 31. Canadian Institute of Mining and Metallurgy, Westmount, Quebec, pp. 87–99. Broughton, P.L., 1997. Origin of coal basins by salt solution. Nature 270, 420–423. Broughton, P.L., 2013. Devonian salt dissolution-collapse breccias flooring the Cretaceous Athabasca oil sands deposit and development of lower McMurray Formation sinkholes, northern Alberta Basin, Western Canada. Sed. Geol. 283, 57–82. Broughton, P.L., 2015. Syndepositional architecture of the northern Athabasca oil sands deposit, northeastern Alberta. Can. J. Earth Sci. 52, 21–50. Broughton, P.L., 2016. Alignment of fluvio-tidal bars in the middle McMurray Formation: Implications for structural architecture of the Lower Cretaceous Athabasca oil sands deposit, northern Alberta. Can. J. Earth Sci. 53, 896–930. Broughton, P.L., 2017d. Breccia pipe and sinkhole linked fluidized beds and debris flows in the Athabasca Oil Sands: Dynamics of evaporite karst collapse-induced fault block collisions. Bull. Can. Pet. Geol. 65, 200–234. Broughton, P.L., 2017b. Orogeny and hydrothermal karst: stratabound Pb-Zn sulphide deposition at Pine Point, northern Canada. In: Klimchouk, A., Palmer, A., De Waele, J., Auler, A., Audra, P. (Eds.), Hypogene Karst Regions and Caves of the World. Springer International, Cham, Switzerland, pp. 633–646. Broughton, P.L., 2017a. Hypogene karst collapse of the Devonian Prairie Evaporite basin in western Canada. In: Klimchouk, A., Palmer, A., De Waele, J., Auler, A., Audra, P. (Eds.), Hypogene Karst Regions and Caves of the World. Springer International, Cham, Switzerland, pp. 617–632. Broughton, P.L., 2017c. Collapse of the Devonian Prairie Evaporite karst in the Western Canada Sedimentary Basin: Structuration of the overlying Cretaceous Athabasca Oil Sands and regional flow system reversal by subglacial meltwater. In: Kuniansky, E.,

19

Ore Geology Reviews 113 (2019) 103117

P.L. Broughton

Dakota Geological Survey, Report of Investigations 113, Bismark, North Dakota, pp. 39. Lane, D.M., 1959. Dawson Bay Formation in the Quill Lakes-Qu'Appelle Area, Saskatchewan. Saskatchewan Geological Survey, Report 38: Regina, Saskatchewan, pp. 51. LeFever, J., LeFever, R., 2005. Salts in the Williston Basin, North Dakota. North Dakota Geological Survey, Report of Investigations 103, Bismark, North Dakota, pp. 45. Lomas, S., 2018. Technical Report NI 43-101 for Resource Estimation on the Burr Project, Athabasca Potash Inc., Saskatchewan. Lions Gate Geological Consulting, Sechelt, British Columbia, for AMEC Americas Limited, pp. 137. Mackintosh, A.D., McClung, W.C., 2000. The control of a brine inflow and support to the resulting solution cavern in a conventional Saskatchewan potash mine. In: Proceedings, World Salt Symposium, May 2000, Grand Junction, Colorado, pp. 381–386. Mackintosh, A.D., McVittie, G.A., 1983. Geological anomalies observed at the Cominco Ltd. Saskatchewan potash mine. In: McKercher, R.M. (Ed.), Proceedings, First International Potash Technology Conference, October 3-5, 1983, Saskatoon, Saskatchewan, Pergamon, Toronto, pp. 59–64. Maiklem, W.R., 1971. Evaporite drawdown-mechanism for water-level lowering and diagenesis in the Elk Point Basin. Bull. Can. Pet. Geol. 17, 194–233. McIntosh, R.A., Wardlaw, N.C., 1968. Barren halite bodies in the sylvinite mining zone at Esterhazy, Saskatchewan. Can. J. Earth Sci. 5, 1221–1238. McTavish, G., Vigrass, L., 1987. Salt dissolution and tectonics, south-central Saskatchewan. In: Carlson, G., Christopher, J. (Eds.), Proceedings, Fifth International Williston Basin Symposium. Saskatchewan Geological Society, Special Publication 9, Regina, Saskatchewan, pp. 157–168. Meijer Drees, N.C., 1986. Evaporite deposits of Western Canada. Geol. Surv. Can. Pap. 81–18, 118. Meijer Drees, N.C., 1994. Devonian Elk Point Group of the Western Canada Sedimentary Basin. In: Mossop, G.D., Shetson, O. (Comps.), Geological Atlas of the Western Canadian Sedimentary Basin. Canadian Society Petroleum Geologists, Alberta Research Council, Special Report 4, Chap. 10, pp. 129–148. Morgenstein, N., Sepehr, K., 1991. Time-dependent hydraulic fracturing in potash mines. Int. J. Rock Mech. Min. 28, 187–197. Mosaic Corporation, 2016. Form 10-K for the Year Ended December 31, 2016, Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. Mosaic Corporation, Plymouth, Minnesota. Mosaic Corporation, 2017. Form 10-K for the Year Ended December 31, 2017, Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. Mosaic Corporation, Plymouth, Minnesota. Mossop, G.D., Shetsen, I., 1994. Geological Atlas of the Western Canada Sedimentary Basin. Canadian Society Petroleum Geologists, Alberta Research Council, Special Report 4. Nemeth, B., Danyluk, T., Prugger, A., 2002. Benefits of 3D poststack depth migration: case study from the potash belt of Saskatchewan. Abstracts and Proceedings, 2002 CSEG Geophysics Convention May 12-14, Calgary, Alberta, Canadian Society Exploration Geophysics, 2002. Nicolas, M., 2015. Potash deposits in the Devonian Prairie Evaporite, southwestern Manitoba (parts of NTS 62F and K). Manitoba Geological Survey, 2015 Report of Activities, Winnipeg, Manitoba, pp. 97–105. Oldale, H.S., Munday, R.J., 1994. Devonian Beaverhill Lake Group of the Western Canada Sedimentary Basin. In: Mossop, G.D., Shetson, O. (Comps.), Geological Atlas of the Western Canadian Sedimentary Basin. Canadian Society of Petroleum Geologists, Calgary, and Alberta Research Council, Special Report 4, Chap. 11, pp. 149–163. Palombi, D., 2008. Regional hydrogeological characterization of the northeastern margin in the Williston Basin. M.Sc. thesis. University of Alberta, Edmonton. Pauls, J.D., 2017. Feasibility study of a continuous bore-bolter in an underground potash mine. M.Sc. thesis. University of Saskatchewan, Saskatoon, Saskatchewan, pp. 161. Prugger, A.F., 1985. Microseismic studies related to potash mining. M.Sc. thesis. University of Saskatchewan, Saskatoon, Saskatchewan, pp. 156. Prugger, F.F., Prugger, A.F., 1991. Water problems in Saskatchewan potash mining – what can be learned from them? Can. Min. Metall. Bull. 84, 58–66. Rauche, H., van der Klauw, S., Piché, L., Buckner, E., 2016. KCl and MgCl2 Mineral Reserve and Resource Estimate for the Wynyard Carnallite Project, Subsurface Mineral Lease KL 246, KL 247 and KLSA 010, Saskatchewan. Ercosplan Geotechnik, North Rim Exploration, Amec Foster Wheeler, for Karnalyte Resources, Saskatoon, Saskatchewan, pp. 251. Schneider, C., Grobe, M., 2013. Regional Cross-Sections of Devonian Stratigraphy in Northeastern Alberta (NTS 74D, E). Alberta Geological Survey, Open File Report, 2013-05, Edmonton, Alberta, pp. 25. Sepehr, K., Stimpson, B., 1988. Potash mining and seismicity: a time-dependent finite element model. Int. J. Rock Mech. Min. 25, 383–392. Smith, D., Pullen, J., 1967. Hummingbird structure of southeast Saskatchewan. Bull. Can. Pet. Geol. 15, 468–482. Smith, R.C., 1988. The conversion of a flooded potash mine to a solution mine (turning a lemon into lemonade). Presentation, Annual Meeting, International Fertilizer Association, Phoenix, Arizona, (preprint), pp. 8. Soroka, T., Lahonen, C., 2018. The history and evolution of the Patience Lake solution potash mine, Saskatchewan. Technical Conference, Solution Mining Research Institute, Salt Lake City, Utah, (preprint), pp. 13. Stoner, E., Mackintosh, A.D., 2011. Technical Report on Vanscoy Potash Operations, Vanscoy, Saskatchewan, Vanscoy National Instrument 43-101. Agrium, Saskatoon, Saskatchewan, pp. 138. Thomas, G., 1974. Lineament block tectonics: Williston-Blood Creek basins. AAPG Bull. 58, 1305–1322. Van der Voo, R., 1988. Paleozoic paleogeography of North America, Gondwana, and

and Seismicity in Mines. Johannesburg, South Africa. Gendzwill, D.J., Horner, R.B., Hasegawa, H.S., 1982. Induced earthquakes at a potash mine near Saskatoon, Canada. Can. J. Earth Sci. 19, 466–475. Gendzwill, D.J., Martin, M., 1996. Flooding and loss of the Patience Lake Potash Mine. Can. Min. Metall. Bull. 89, 62–73. Gendzwill, D.J., Prugger, A.F., 1988. Seismic activity in a flooded Saskatchewan potash mine. In: Second International Symposium on Rockburst and Seismicity in Mines. University of Minnesota, pp. 139–148. Gendzwill, D.J., Stauffer, M., 2006. Shallow faults, upper cretaceous clinoforms, and the colonsay collapse, Saskatchewan. Can. J. Earth Sci. 43, 1859–1875. Golder Associates, 2011. Vale Kronau Project Proposal, August 2011, Golder Associates, Saskatoon, Saskatchewan. Prepared for Vale Potash Canada, Regina, Saskatchewan, pp. 75. Grasby, S., Betcher, R., 2000. Pleistocene recharge and flow reversal in the Williston Basin, central North America. J. Geochem. Explor. 69–70, 403–407. Grasby, S., Betcher, R., 2002. Regional hydrogeochemistry of the carbonate rock aquifer, southern Manitoba. Can. J. Earth Sci. 39, 1053–1063. Grasby, S., Chen, Z., 2005. Subglacial recharge in the Western Canada Sedimentary Basin - impact of Pleistocene glaciations on basin hydrodynamics. Geol. Soc. Am. Bull. 117, 500–514. Grasby, S., Osadetz, K., Betcher, R., Render, F., 2000. Reversal of the regional-scale flow system of the Williston Basin in response to Pleistocene glaciation. Geology 7, 635–638. Grobe, M., 2000. Distribution and thickness of salt within the Devonian Elk Pont Group, Western Canada Sedimentary Basin. Alberta Geological Survey, Earth Science Report 2000-02, Edmonton, Saskatchewan, pp. 12. Halabura, S.P., Gebhardt, E., Kuchling, K., 2005. Technical Report for Subsurface Mineral Permit KP 286, Jansen Area, Saskatchewan. North Rim Exploration, Saskatoon, Saskatchewan, pp. 67. Halabura, S.P., Hardy, M.P., 2007. An overview of the geology of solution mining of potash in Saskatchewan. Solution Mining Research Institute Fall 2007 Conference, Halifax, Nova Scotia, pp. 17. Hambley, D.F., Yu, B., Brebner, J., 2015. NI 43-101 Technical Report Summarizing the Scoping Study for a Pilot-Scale Selective Solution Mining Operation on the Milestone Project (Subsurface Mineral Lease KLSA 008) Saskatchewan. Agapito Assoc., Grand Junction, Golden, Colorado, for Western Potash Corporation, pp. 149. Hamilton. W.N., Olson, R.A., 1994. Mineral resources of the Western Canada Sedimentary Basin. In: Mossop, G.D., Shetsen, I. (Eds.), Geological Atlas of the Western Canadian Sedimentary Basin, Canadian Society of Petroleum Geologists, Alberta Research Council, Special Report 4, 483-502. Hamilton, W.N., 1971. Salt in east-central Alberta. Alberta Geological Survey, Bulletin 29, Edmonton, Saskatchewan, pp. 43. Hardie, L., 1996. Secular variation in seawater chemistry: An explanation for the coupled secular variation in the mineralogies of marine limestones and potash evaporites over the past 600 m.y. Geology 24, 279–283. Hardy, M.P., Hambley, D.F., O’Hara, P., Pekeski, D., Vogelsand, G., 2011. Technical Report NI 43-101 Summarizing the Preliminary Feasibility Study for a Potash Solution Mine on the Milestone Project (Subsurface Mineral Lease KLSA 008), Saskatchewan. Agapito Associates, Grand Junction, Colorado, AMEC Americas Ltd., Saskatoon, Saskatchewan, for Western Potash, Vancouver, British Columbia, pp. 142. Hendry, M.J., Barbour, S.L., Novakowski, K., Wassenaar, L.I., 2013. Paleohydrogeology of the Cretaceous sediments of the Williston Basin using stable isotopes of water. Water Resour. Res. 49, 4580–4592. Holter, M.E., 1969. The Middle Devonian Prairie Evaporite of Saskatchewan. Saskatchewan Geological Survey, Report 123, Regina, Saskatchewan, pp. 134. Husband, W.H., Ozsahin, S., 1967a. Solution Mining Method of Potash Production. Saskatchewan Research Council, Eng. Division Report E67-11, Saskatoon, Saskatchewan, pp. 23. Husband, W.H., Ozsahin, S., 1967b. Comparison of the solution mining and refining of potash with conventional methods in Saskatchewan. Can. Min. Metall. Bull. 60, 560–567. Jones, P.R., Prugger, F.F., 1982. Underground mining in Saskatchewan potash. Min. Eng. 34, 1677–1683. Kendall, A.C., 1975. The Ashern, Winnipegosis and Lower Prairie Evaporite Formations of the commercial potash areas. In: Christopher, J.E., Macdonald, R. (Eds.), Saskatchewan Geological Survey, 1975 Summary of Investigations. Saskatchewan Geological Survey, Regina, Saskatchewan, pp. 61–65. Kent, D.M., Christopher, J.E., 1994. Geological history of the Williston Basin and Sweetgrass Arch. In: Mossop, G.D., Shetsen, I. (Eds.), Geological Atlas of the Western Canada Sedimentary Basin. Canadian Society of Petroleum Geologists, Alberta Research Council, Special Report 4, pp. 421–430. Kent, D., 1974. Relationship between hydrocarbon accumulations and basement structural elements in the northern Williston basin. In: Parslow, G. (Ed.), Fuels: a Geological Appraisal. Saskatchewan Geological Society, Special Publication 2, pp. 63–80. Keys, D.A., Wright J.V., 1965. Geology of the I.M.C. potash deposit, Esterhazy, Saskatchewan. In: Rau, J.L. (Ed.), Proceedings, Second Symposium on Salt, Cleveland, Ohio, pp. 95–101. Koehler, G.D., Kyser, T.K., Danyluk, T., 1990. Stable isotope evidence for the petrogenesis of carnallite in the Middle Devonian Prairie Evaporite Formation, Saskatchewan. In: Summary of Investigations 1990, Saskatchewan Geological Survey, Miscellaneous Report 90-4, Regina, Saskatchewan, pp. 218–222. Koehler, G.D., 1997. The geochemistry and petrogenesis of carnallite and its relationship to the diagenesis of the Devonian Prairie Evaporite Formation. Ph. D. thesis, University of Saskatchewan, Saskatoon, pp. 228. Kruger, N., 2014. The Potash Members of the Prairie Formation in North Dakota. North

20

Ore Geology Reviews 113 (2019) 103117

P.L. Broughton

Saskatchewan. In: Saskatchewan Geological Survey, 2009 Summary of Investigations, Misc. Report 2009-4.1, Paper A-4, Regina, Saskatchewan, pp. 28. Yang, C., Jensen, G.K.S., Berenyi, J., 2009e. Salt-back thickness map of the Esterhazy Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 2009-28, Regina, Saskatchewan. Yang, C., Jensen, G.K.S., Berenyi, J., 2009f. Salt-back Thickness Map of the Belle Plaine Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 2009-29, Regina, Saskatchewan. Yang, C., Jensen, G.K.S., Berenyi, J., 2009g. Salt-back Thickness Map of the Patience Lake Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 2009-27, Regina. Yang, C., Schuurmans, E., Love, M., 2018a. Updated Isopach Map of the Esterhazy Member of the Devonian Prairie Evaporite in Saskatchewan; Saskatchewan Geological Survey, Open File 2018-1, Map 3, Regina. Yang, C., Schuurmans, E., Love, M., 2018b.Updated Isopach Map of the Belle Plaine Member of the Devonian Prairie Evaporite in Saskatchewan; Saskatchewan Geological Survey, Open File 2018-1, Map 2, Regina. Yang, C., Schuurmans, E., Love, M., 2018c. Updated Isopach Map of the Patience Lake Member of the Devonian Prairie Evaporite in Saskatchewan; Saskatchewan Geological Survey, Open File 2018-1, Map 1, Regina. Yang, C., 2016. Homogenization temperatures of all-liquid fluid inclusions in halite from the Middle Devonian Prairie Evaporite, southern Saskatchewan. In Saskatchewan Geological Survey, 2016 Summary of Investigations, Misc. Report. 2016-4.1, Regina, pp. 13.

intervening displaced terrains: comparisons of paleomagnetism with paleoclimatology and biographical patterns. Geol. Soc. Am. Bull. 100, 311–324. Wardlaw, N.C., 1968. Carnallite-sylvite relationships in the Middle Devonian Prairie Evaporite Formation, Saskatchewan. Geol. Soc. Am. Bull. 79, 1273–1294. Wardlaw, N.C., Watson, D.W., 1966. Middle Devonian salt formations and their bromide content, Elk Point area, Alberta. Can. J. Earth Sci. 3, 263–275. Wittrup, M.B., Kyser, L., 1990. The petrogenesis of brines in Devonian potash deposits of western Canada. Chem. Geol. 82, 103–128. Woroniuk, B., Tipton, K., Grasby, S., McIntosh, J.C., Ferguson, G., 2019. Salt dissolution and permeability in the Western Canada Sedimentary Basin. Hydrogeol. J. 27, 161–170. Worsley, N., Fuzesy, A., 1979. Potash-bearing members of the Devonian Prairie Evaporite of southeastern Saskatchewan, south of the mining area. Economic Geology 74, pp. 377–388. Yang, C., Jensen, G.K.S., Berenyi, J., 2009a. Isopach Map of the Esterhazy Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 2009-25, Regina, Saskatchewan. Yang, C., Jensen, G.K.S., Berenyi, J., 2009b. Isopach Map of the Belle Plaine Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 200926, Regina, Saskatchewan. Yang, C., Jensen, G.K.S., Berenyi, J., 2009c. Isopach Map of the Patience Lake Member of the Prairie Evaporite Formation. Saskatchewan Geological Survey, Open File 200924, Regina, Saskatchewan. Yang, C., Jensen, G.K.S., Berenyi, J., 2009d. The stratigraphic framework of the potashrich members of the Middle Devonian Upper Prairie Evaporite Formation,

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