Summary:
he geological focus of this Technical Report is on the aquifer system within the Late Devonian (Frasnian) dolomitized reef structure of the Woodbend Group, Leduc Formation, that conformably overlies the carbonates of the Beaverhill Lake Group. The reef structure is called the Sturgeon Lake Reef Complex, and the LithiumBank Property encompasses most of the complex.
The Leduc Formation is defined by subsurface oil and gas exploration (n=242 wells) that define the true vertical depth of the Leduc Formation at depths of between -2,337.6 m and -3,050.6 m (average -2,619.9 m) below the Earth’s surface. The Leduc reef has a thickness of approximately 230 to 380 m (average and maximum thicknesses of 206 m and 408 m) along a southwest to northeast cross section at the Boardwalk Property (Hydrogeological Consultants Ltd., 2012).
The Beaverhill Lake Group (Swan Hills aquifer) and the Woodbend Group (Leduc aquifer) were thought to be hydraulically connected due to historical government interpretation of Hitchon et al. (1995). A hydrological assessment conducted by HCL has demonstrated the two units – at least in LithiumBank’s Boardwalk Property area – are in fact not connected.
The brine is hypersaline. Reported total dissolved solids (TDS) concentrations of 77 Leduc samples ranged from 113,117 to 265,921 mg/L, with an average of 199,995 mg/L (Hydrogeological Consultants Ltd., 2012).
Mineralization
Lithium mineralization within the Devonian Leduc Formation aquifer is in solution within the brine; hence it is not observed in the physical state. Accordingly, the best way to provide discussion on mineralization is to review the geochemical nature of the brine.
The average crustal abundance of lithium is approximately 17-20 ppm with higher abundances in igneous (28-30 ppm) and sedimentary rocks (53-60 ppm; Evans, 2014; Kunasz, 2006). Hence, the elevated lithium content in Devonian brines in the Alberta basin portion of the Western Canada Sedimentary Basin define the mineralization being discussed in this technical report.
The elevated K/Br, in conjunction with high Li/Br and increasingly radiogenic 87Sr/86Sr values indicate an influence of a hydrothermal fluid(s) and/or mobilization of silicate-bearing fluids from either the crystalline basement or the immature siliciclastic deposited above the basement (basal Cambrian sandstone, Granite Wash or the Gilwood Member), to the Devonian brine (Eccles and Berhane, 2011; Huff, 2019). A cluster of Leduc Formation brine analyses has low K/Br (< 1.5) and possible that the Li-enriched brine formed in another environment perhaps through dissolution of Li-bearing late-stage evaporite minerals into midDevonian seawater evapo-concentrated to, but not beyond, halite saturation (Huff, 2019).
Additional Leduc Formation brine attributes include a relative density of 1.214 g/cm3 , observed pH of 7.10, measured TDS of 246,700 mg/L, conductivity of 214,000 uS/cm and total alkalinity as CaCO3 of 290 mg/L. The analytical charge imbalance is -1.52%. The calculated charge imbalance, using the brine density and TDS is -1.68%.
The QP-analyzed brine results correlate well with a review of historically documented Leduc Formation fluid-quality data accessed from AccuMap (n=77 analyses). These data record TDS concentrations of between 110,700 and 278,554 mg/L TDS, with an average TDS concentration of 214,683 mg/L.
The major ions are classified as having predominantly sodium and calcium cations and predominantly chloride anions. The average formation temperature in the DST results analyzed by Melange was 82°C.
Deposit Types
There are over 100 minerals that contain lithium, but only a few of these are currently economic to extract. Lithium is extracted from two main categories of deposits: mineral and brine.
Brine deposits can be separated into 1) surface or near-subsurface continental deposits (salars), and 2) confined aquifer deposits that occur in deep, subsurface basial aquifers. Continental brine occurs in endorheic basins where inflowing surface and groundwater is moderately enriched in lithium. All currently producing lithium brine operations are represented by continental brine deposits.