The importance of considering the hydrodynamics of the saline interface in the managements of mineral resources and ecosystems of salt flats
DOI:
https://doi.org/10.21701/bolgeomin.132.1-2.013Keywords:
brine, lithium, groundwater, salt flat, saltwater intrusionAbstract
Salt flats are an important source of minerals and especially of lithium. In addition, lakes and wetlands of high ecological value are frequently associated with the saline interface zone (mixing zone) resulting from the density contrast between the freshwater coming from the rainfal infiltration on the mountains and the brine produced mainly by evaporation in the depressions. This zone is characterized by vertical flows that condition the hydrodynamics at a basin scale. It is necessary to establish a methodology that allows the incorporation of the effect of the saline interface into groundwater models for the management of the mineral resources and ecological values. This methodology consists of 3 steps: 1) physical-chemical data collection in the field, 2) 3D mapping of the mixing zone and 3) numerical modelling.
A three-dimensional (3D) mapping of the mixing zone of the Salar de Atacama is presented. The mixing zone geometry was interpreted using a numerical flow and solute transport model. The results from the model show a slope of the mixing zone that is similar to that obtained with the field data, which is more relaxed than in the previous models that considered a homogeneous porous medium. The higher the permeability of the upper aquifer is, the lower the slope and the shallower the mixing zone become. The presence of a few metres of highly permeable materials (alluvial fans or karstified evaporites) in the upper stratigraphic units of the salt flats is enough to condition the regional geometry of the saline interface.
The use of this 3D mapping is proposed as a basis for the correction of the freshwater and mixing water heads to brine heads to reduce the computational cost of 3D numerical models for groundwater management in salt flats.
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