The results of geophysical survey suggest that the deepest part of the basin is in the center, where salar deposits may reach up to 300 m thick.

The results indicate that the eastern and northern basins of the Salar de Hombre Muerto are floored largely by clastic material with thin horizons of precipitated borax, halite, gypsum, and calcite.

Field observations indicated groundwater associated with each of the sand units, so that they may be termed aquifers. The clay units did not produce water and in each case they created a confining bed to the underlying sand unit, so that they may be termed aquicludes, or possibly aquitards (the latter implies the possibility of slow leakage across the bed). Unconfined groundwater in sand unit 1 occurs between 0.7- 0.9 m depth. Sand unit 2 averages 1.8-2.3 m depth. Both these units produced relatively small quantities of fluid. Sand unit 3 produced greater quantities of fluid between 4.1 to >4.7 m depth, and is thus likely to have higher permeability. Sand unit 4 occurred at only a few locations towards the south of the area investigated.

The base of the second clay unit has a distinctive black, organic horizon that can be correlated across the salar. Two depocenters can be identified in the central southern part of the eastern basin, and towards the north, with the source of the sediment infill, looking to be sourced from the Rio Los Patos delta region.

The total sand thickness of all Sand Units in the pits is greatest along the toe of the Rio Los Patos delta, where it reaches >4 m in total. Towards the northern depocenter, the Sand Units reach 3 m thickness. The sand fraction again emphasizes the importance of the input of sediment from the Rio Los Patos and the northern depocenter, both of which show >80% sand content in the pit sections.

Mineralization.
Brine prospects differ from solid phase industrial mineral prospects by virtue of their fluid nature. Therefore, the term ‘mineralization’ is not strictly relevant to a brine play, so that here the brine is considered; its flow regime, and its physical and chemical properties.

The distribution of density in the eastern part of the salar shows a general increase away from the Rio Los Patos delta, where relatively fresh water (density ~1.0 gram per centimeter cubic to minus the third degree) enters. As the fluid moves through the more permeable units away from the delta, concentrations, and hence density, rapidly increase to >1.1 grams per centimeter cubic to minus the third degree. This increase is the result of evaporation around the toe of the delta where groundwater is relatively close to the surface. Over much of the eastern basin the density is greater than 1.15 grams per centimeter cubic to minus the third degree, although a tongue of slightly lower density extends from the delta north of the Farralon Catal.

Groundwater enters the salar from the Rio Los Patos delta, from where flow bifurcates with a significant flow extending towards the northwest. Low fluid elevations, or sinks, are seen towards the north and towards the southwest.

The chemistry of the fluids confirms that there is only one brine type within the salar, originating from the evaporation of influent waters.

As calcium reaches a concentration of approximately 40 mmol/l in minus first degree gypsum starts to precipitate and the fluid becomes enriched in sulphate. Throughout the brine evolution sodium and chloride react conservatively, gradually increasing in concentration, and halite saturation which by analogy with other salars in the region occurs at approximately 280 gm/l in minus first degree NaCl.

The distribution of lithium and potassium in the eastern basin at Hombre Muerto are shown that maximum concentrations are associated with the areas of higher density, > 1000 mg/l minus first degree Li, and >10,000 mg/l minus first degree K in the central south, with subsidiary peaks of >800 mg/l minus first degree Li and >8,000 mg/l minus first degree K towards the north.

The area is underlain by the extensive APVC (the Altiplano-Puna Volcanic Complex magma) chamber at depths of only 4 km and it seems likely that this could be the ultimate source, being transferred to the surface via volcanic activity, especially hydrothermal vents. However it is not known whether such transference was direct, or indirect as a result of the leaching of lithium-bearing volcano-clastic sediments, or by the recycling of trapped lithium-bearing solutions. It is known that several hot springs bordering the salar drain directly into the basin. Another possible source of lithium may be related to the borate deposits in the area.

Well fields.
The approach to recovery of brine has focused on the use of two well fields (Southwest and East). The two locations for the proposed well fields were determined based on brine quality, extent of the brine aquifer, and the ability to pump the brine aquifer at sufficient quantity and rate to support filling and maintaining levels of the evaporation ponds. Pump tests and daily samples collected showed little variation in lithium and potassium concentrations, indicating dilution of produced brine was not evident during the 30-day pumping periods. A total of 24 well field pumps will provide a continuous flow of brine to the liming and evaporation ponds.

The ultimate production level for the plant is determined by evaporation rate, which varies depending on season. In summer months when temperatures are highest and rainfall low, evaporation rates can double. In these periods additional wells will be brought online to increase the flow of brine to the evaporation ponds.

Well pumping rate and lime plant throughput can be operated at 40% above the average to take advantage of high evaporation rates.

Ponds and Evaporation.
Extracted brine from the well fields is pumped to the liming ponds for magnesium removal as the first step of the brine purification process. Magnesium is precipitated as magnesium hydroxide Mg(OH)2 after reacting it with a milk of lime solution. Following reaction, brine is pumped into the active lime settling pond where magnesium hydroxide solids settle to the pond floor and clarified brine overflows into a pumping well.

Halite Ponds.
The function of the halite ponds (rock salt, NaCI) is to concentrate limed brine to its potassium chloride saturation limit and remove the sodium chloride (NaCl). This is accomplished through evaporation as a result of solar radiation, wind, and temperature. The halite ponds (lined) consist of five strings (4 operating, 1 in harvest) with a total surface area of 7.7 square kilometres and designed to minimise entrainment of concentrated brine in the halite. The crystallised salts rich in sodium chloride accumul ........