Size and Structure of Deposits Basins that host lithium brines...

Size and Structure of Deposits
Basins that host lithium brines range in area by more than three orders of magnitude. The floor
of Salar de Uyuni has an area of about 14,000 square kilometers (km2
) and a total catchment of about
47,000 km2
. At the other end of the spectrum, the floor of Clayton Valley has an area of about 100 km2
and a catchment of about 1,400 km2 (areas were measured using ARC-GIS from a global 90-m SRTM
DEM). Clayton Valley is the topographically lowest of at least five adjacent basins that are
hydrologically linked by groundwater flow (Zampirro, 2004). In this case, it is the combined area of all
five linked catchments that matters, making the effective area of the Clayton Valley Li-brine system
much larger.
Active faulting appears to be involved in all lithium basins. Fault-related subsidence creates
accommodation space, without which only a thin veneer of basin sediments could accumulate. A thick
basin fill is needed to provide an aquifer of sufficient volume to hold a viable brine resource. In contrast,
shallow, superficial basins in cratonic regions such as the Sahara Desert lack fault control and are not
known to be prospective for lithium brines. Some basins are cut by active intrabasinal faults. Brine
pools in Clayton Valley and Salar de Atacama are localized along active intrabasinal faults that control
the distribution of aquifers and also influence groundwater movement patterns. These intrabasinal faults
are known from boreholes and have no surface expression (Zampirro, 2004; Jordan and others, 2002).
Because they are contained by aquifers of various geometries, lithium brines are localized in the
subsurface rather than being present everywhere at depth. At Salar de Atacama, the brine is hosted in
the porous, upper 30 meters of the salar’s halite nucleus (Garrett, 2004). Little is known about the
potential of brine aquifers at depth in Salar de Atacama. At Clayton Valley, brines are pumped from six
gently dipping aquifers that are variously composed of ash, fanglomerate, tufa, and halite (Zampirro,
2004).
Geologic Assessment Guidelines
Characteristics that appear to be essential for lithium resource potential are an arid climate and a
closed, tectonically active basin. Another likely requirement—or at least a favorable characteristic—is
elevated heat flow as evident from young volcanoes or hot springs. Source rocks such as felsic, vitric
tuffs that have abundant and readily leached lithium are favorable but perhaps not essential, since
lithium is present in most crustal rocks at tens of parts per million (ppm). Another favorable indication
of lithium brines is the existence of hectorite, a mineral that can be detected using ASTER remote
sensing (B. Rockwell, USGS, written commun., 2010).