Summary:
Salar de Cauchari (the salar) is a mixed (mature and immature) style salar, with a halite nucleus in the centre of the salar overlain with up to 50 m of fine grained (clay) sediments. The halite core is interbedded with clayey to silty and sandy layers. The salar is surrounded by relative coarse grained alluvial and fluvial sediments. These fans demarcate the perimeter of the actual salar visible in satellite images and at depth extend towards the centre of the salar where they form the distal facies with an increase in sand and silt content. At depth (between 300 m and 600 m) a deep sand unit has been intercepted in several core holes in the southeast sector of the project area.
Salar de Cauchari is located towards the centre of the Puna Plateau. The Puna is an elevated plateau in northern Argentina which has been subject to uplift along thrust systems inverting earlier extensional faults. The Puna is host to numerous large ignimbrites and stratovolcanoes.
Evaporite minerals (halite, gypsum) occur disseminated within clastic sequences in the salar basins and as discrete evaporite beds. Based on the drilling campaigns carried out in the salar between 2011 and 2018, six major geological units were identified and correlated from the logging of drill cuttings and undisturbed core to a general depth of over 600 m. These units are characterised according to the relative abundance of gravels, sands, silts, clays and evaporites present within each grouping. No drill hole has reached bedrock.
Salar aquifers at Cauchari host lithium-rich brine in the pore space between sediment grains and in primary or secondary fractures. Owing to the depositional environment present at the time the aquifers were formed, these aquifers consist of horizontal to sub-horizontal clastic sediments and evaporites. The package of sedimentary and evaporitic aquifers that host lithium brine beneath the salar surface are collectively referred to as the brine reservoir. Major geologic units were grouped into four hydrogeologic units based on their hydraulic properties, including specific yield and permeability: distal alluvial fans, a clay aquitard, a semiconfined halite unit with interbedded clastics, and a deep sand unit that occurs at depths greater than 300 m bgs.
The salar occurs in a closed (endorheic) basin without external drainage, in a dry desert region where evaporation rates exceed stream and groundwater recharge rates, preventing lakes from reaching the size necessary to form outlet streams or rivers. Evaporative concentration of surface and shallow groundwater over time in these basins leads to residual concentration of dissolved minerals enriched in the types of constituents present at Cauchari: sodium, potassium, chloride, sulphate, carbonate species, boron and lithium. The brines at Cauchari are nearly saturated in sodium chloride with an average concentration of total dissolved solids of 290 g/l. The average density and lithium grade is approximately 1.19 g/cm3 and 500 mg/l, respectively.
Water enters the salar from both streams and groundwater discharges from basin-bounding alluvial fans (and potentially from adjacent rock formations). Rio Tocomar entering Cauchari from the south and Rio Archibarca from the west are the only two perennial surface water features in the project area. Other surface water flows are intermittent and occur primarily during summer months following intense rainfall events.
The salar is an endorheic basin, resulting in evaporation and plant transpiration being the primary processes for water outflow, followed by groundwater pumping for brine processing at neighbouring operations.
Dimensions:
The Mineral Resource model covers 117.7 km2. The top coincides with the brine level in the salar, measured by monitoring wells and geophysical TEM and SEV tests.
The lateral boundaries are defined based on the Cauchari tenements and by the brine / groundwater interface along the eastern and western limits of the salar as based on the physical TEM and SEV drill holes.
The base of the model varies across its domain (nominally 400 m) and coincides with a surface created from the bottom of the drill holes, which occur above the sediment-bedrock contact that forms the conceptual base of the deposit as interpreted from geophysical surveys.