Summary:
One of the most important characteristics that define the Geological Province of Puna, is the presence of evaporitic basins, where important deposits of borates, sodium sulphate, and lithium salts occur. The Salar de Tolillar occupies one of these endorheic (internally drained) basins.
Deposit Type
Based on the available information, Salar de Tolillar appears to be a relatively immature salar. Although evaporites and brine occur, a well-developed halite core typically associated with more mature salars, such as Salar de Arizaro, Salar de Hombre Muerto, and others, does not appear to exist. Basin margins are interpreted to be fault controlled. The margin of the basin is dominated by Ordovician crystalline rocks. Volcanic units are not known to occur in the basin, but may be deeper than 208 m in the north part of the basin, or in the south part of the Tolillar Project that has yet to be drilled. Depth to bedrock is interpreted to be considerably deep below land surface based on VES geophysical surveys (Tecnología y Recursos, 2017), but because it appears to be variable throughout the Tolillar Project and was not encountered during exploration drilling, depth to bedrock is considered unknown.
Ordovician bedrock is expected to have low hydraulic conductivity and should approximate a “no-flow” groundwater boundary during extraction of brine from basin fill deposit aquifers by future pumping wells. Fine-grained lacustrine deposits and interbedded halite in the upper part basin are interpreted to have relatively low hydraulic conductivity based on results of aquifer testing at well DDHB-01 (Table 6-10) In other basins, highly permeable halite occurs in the upper parts of the salar where intercrystalline porosity is high; however, based on exploration drilling, very little halite occurs in the north part of the concession. Coarser-grained clastic units encountered during drilling are believed to be moderately permeable and should be able to provide brine to properly constructed production wells.
The principal sources of water entering the Tolillar Project area are from surface water coming into the basin from the basin margins. To date, surface water flow has not been formally measured. Some groundwater inflow from natural recharge along the mountain fronts via alluvial fans is also believed to exist. In both cases, there appears to be limited mixing of the freshwater and brine in the basin due to density differences. As a result, the freshwater entering the Tolillar Project tends to stay in the upper part of the aquifer system on the edges of the basin, without moving to the center part of the Salar. These freshwater discharge areas tend to support altiplanic vegetation. Evaporation of freshwater from the basin over time results in concentration of the dissolved minerals and ultimately results in brine generation.
Mineralization
The mineralization for the Tolillar Project consists of a lithium-enriched brine that is contained within the pore spaces of the sedimentary strata in the salar basin in the upper several hundred meters of the basin, in the evaporite, alluvial, and colluvial sediments. The mineralization of the brine has occurred over a long period of time via evapoconcentration of the brine, which enriched the brine in lithium because lithium does not precipitate to a solid form in the brine. Except where there is a strong influx of freshwater to the salar basin, like in the north pert of the property, the entire aquifer system is a lithium-enriched brine with generally uniform chemistry. Approximate average lithium concentration in undiluted brine ranges from about 200 – 350 mg/L.
The boundaries of the mineralization are suspected to be the fault-controlled, hard rock basin boundary, although some lithium-enriched brine may be contained in the fractures and/or pores of the rocks that form the basin boundary. Detailed distribution and chemical composition of the brine in the salar sediments is not currently known, although an area of non- mineralized freshwater occurs in the northern concessions in the uppermost part of the sedimentary sequence; thickness of this unmineralized freshwater is not known.
Conceptual Model of Salar de Tolillar
Based on the available information, Salar de Tolillar appears to be a relatively immature salar. Although evaporites and brine occur, a well-developed halite core typically associated with more mature salars, such as Salar de Arizaro, Salar de Hombre Muerto, and others, does not appear to exist. Basin margins are interpreted to be fault controlled. The margin of the basin is dominated by Ordovician crystalline rocks. Volcanic units are not known to occur in the basin, but may be deeper than 208 m in the north part of the basin, or in the south part of the Project that has yet to be drilled. Depth to bedrock is considered to be unknown.
Ordovician bedrock is expected to have low hydraulic conductivity and should approximate a “no-flow” groundwater boundary during extraction of brine from basin fill deposit aquifers by future pumping wells. Fine-grained lacustrine deposits and interbedded halite in the upper part basin are interpreted to have relatively low hydraulic conductivity based on results of aquifer testing at well DDHB-01. In other basins, highly permeable halite occurs in the upper parts of the Salar where intercrystalline porosity is high; however, based on exploration drilling, very little halite occurs in the north part of the concession.
Coarser-grained clastic units encountered during drilling are believed to be moderately permeable and should be able to provide brine to properly constructed production wells.
The principal sources of water entering the Tolillar Project area are from surface water coming into the basin from the basin margins. To date, surface water flow has not been formally measured. Some groundwater inflow from natural recharge along the mountain fronts via alluvial fans is also believed to exist. In both cases, there appears to be limited mixing of the freshwater and brine in the basin due to density differences. As a result, the freshwater entering the Tolillar Project tends to stay in the upper part of the aquifer system on the edges of the basin, without moving to the center part of the Salar. These freshwater discharge areas tend to support altiplanic vegetation. Evaporation of freshwater in the basin over time results in concentration of the dissolved minerals and ultimately results in brine generation.