Summary:
Mineral Deposit
Intrepid’s Wendover operation produces potash by transporting subsurface potassium-rich brines to the surface where they areexposed to western Utah’s arid climate. The aqueous portion of the brine is removed through evaporation, allowing the evaporiteminerals to precipitate and be collected for further processing. Because the potash is derived from subsurface brines, the mineral depositis best represented by characteristics of the aquifer(s) containing the brine.
The shallow-brine aquifer, as it is called, exists within the near-surface carbonate mud layer. The carbonate mud transitions to theless-permeable lacustrine deposits at 20–30 ft depth. Brine extraction involves excavating a network of ditches, which allow the natural inflow of aquifer fluids, thereby exposing the brine to dry atmospheric conditions.
Significant Mineralized Zones
The zones of mineralization at Wendover are defined by the presence of potash-rich brines. These brines are known to occur in two out of three local aquifers: the shallow-brine aquifer and the deep-brine aquifer. The third aquifer, which is not potash-bearing and occurs stratigraphically between the other two, is the alluvial-fan aquifer.
The shallow-brine aquifer is a near-surface aquifer and serves as the primary source of potash-rich brine. It is contained in the highly permeable salt and gypsum crust and underlying fractured carbonate muds. The alluvial-fan aquifer, the middle of the three, resides in the sand and gravel interbedded with the lacustrine sediments remnant of Lake Bonneville that underlie the playa deposits of the BSF. The alluvial-fan aquifer is brackish, yet is not a source of potassium salts. The deep-brine aquifer exists within the volcaniclastics and conglomerates of the Salt Lake Formation. This aquifer typically occurs at depths greater than 250–300 ft.
Local Geology
The modern Lake Bonneville basin interior is extremely dry, mostly devoid of vegetation, and exhibits very little topographic relief. The lithology of the interior, away from what once were islands and shoreline, is predominantly composed of lacustrine deposits and evaporite minerals, occasionally interbedded with layers of fluvial or fine-grained eolian sediments. Sand and gravel occur more often with increased proximity to the ancient shoreline. Igneous, metamorphic, and sedimentary rocks ranging in age from Cambrian to late Tertiary form the barren slopes and mountain ranges surrounding the basin and provide eroded detrital material often deposited asalluvial fans.
All deposits exposed at the surface of the Bonneville and Pilot Valley playas were deposited by Lake Bonneville or by more recent,very minor lacustrine events. The local surface geology consists of evaporite mineral deposits. Evaporite minerals on the surface of the BSF are concentrated in three lateral zones: (1) a carbonate zone composed mainly of authigenic clay-sized carbonateminerals, (2) a sulfate zone composed mainly of authigenic gypsum, and (3) a chloride zone composed of crystalline halite referred to as ‘the salt crust’ (Lines 1979).
The upper 20 ft of the Lake Bonneville deposits underlying the two playas is composed mainly of dark-gray to dark-brown carbonate muds comprised of clay-size calcite, aragonite, and dolomites. Interbedded with the carbonate muds are gypsum evaporite deposits and the crystalline salt crust (Turk 1969). Underlying the carbonate mud layer are lacustrine deposits (0–200 ft thick), mainly composed of fine-grained sediments. When laterally extensive, these lacustrine deposits serve as a confining unit for meteoric fluids.However, the lacustrine deposits often intermingle with alluvial fan-deposited sand and gravel shed from the Silver Mountains to the northwest. Below the lacustrine and alluvial fan deposits, is a relatively thick sequence of volcaniclastics, conglomerates, tuffs, and sandstones known as the Salt Lake Formation (0–500 ft thick). The Salt Lake Formation is late-Miocene to Pliocene in age and formed through the shedding and reworking of sediments from the adjacent mountains as valley fill into the down-dropping graben of the western Great Salt Lake Desert. Interbedded within this layer are fine-grained units predominantly composed of gypsum, limestone, siltstone, and shale.
Property Geology
Intrepid’s Wendover operations are situated in the western portion of the Great Salt Lake Desert, which itself is located within the Bonneville Lake basin. Because the basin is closed topographically and has no outlet, loss of water is ultimately through evaporation. The Wendover property produces potash from beneath an area termed the BSF. The BSF was formed through the prolonged accumulation of evaporite minerals in conjunction with periodic lacustrine events. Within the property boundary, surface topography is extremely low relief and predominantly composed of evaporitic ‘salt crust.’
Intrepid-Wendover produces potash from the rich saline brines that exist in the subsurface. There are three aquifers known to exist beneath the BSF. These aquifers are, in descending order, the shallow-brine aquifer, the alluvial-fan aquifer, and the deep-brine aquifer. Intrepid produces potash from both the shallow-brine aquifer and the deep-brine aquifer.