Deposit Types
Evaporites and brines form a group of industrial mineral deposits where the commercially valuable commodities are either in solution (brines) or are potentially soluble (evaporites) with the addition of water. This style of deposit typically shows broad lateral continuity, but narrow vertical extents.

Brines are found throughout the Andes region in closed basins (salars) where inflowing waters containing low concentrations of metal are concentrated over time due to evaporation, until they become saturated and begin to precipitate out to form evaporites. Various thermodynamic constraints determine the order in which minerals precipitate.

The Mariana Project is a typical salar brine, containing lithium, potassium and boron within permeable aquifers.

Mineralization
The mineral commodities sought at the Mariana Project are metal ions dissolved within brines. Lithium salts are much more soluble than potassium and sodium, which tend to precipitate forming halite units.
The brines are subject to hydrogeological flow regimes allowing replenishment of brines that are extracted from the system.

The observation of brine within all drillholes across Salar de Llullaillaco basin suggests the existence of a connected unconfined brine-bearing system. The spatial distribution of lithology, lithological description and grain size distribution plus other associated elements, such as secondary porosity, were the most relevant aspects that led Geos to define a hydrogeological conceptual model that apportions the brinebearing complex into, at least, eight lithology sequences within the interconnected unconfined aquifer. Determination of the dominant aquitards (semi-impermeable lithologies with very low hydraulic
conductivity) within those units was then undertaken on a similar basis.

The following information was used for definition of the conceptual mineralization model:
• RC and DDH lithological logging, in particular lithology and grain size description
• Geophysical down hole electrical survey data
• TEM survey modelling for correlation with down hole geophysics and between drillholes
• Flow records profile for drillholes
• Geochemistry profiles from drillholes
• Effective porosity analyses of selected samples from 14 diamond drillholes

Mineralization of interest consists of lithium-enriched brines. Lithium (Li) and other potentially economic elements, potassium (K) and boron (B), are interpreted to be leached from volcanic rocks primarily by hydrothermal solutions emanating from deep-seated basin bounding faults and adjacent volcanoes. This also involves circulation of meteoric waters within proposed fault systems and through active stream and spring input flow into the salar.

Based on the drill information, the brines within the project area are interpreted to cover an area of about 135km2 , with an approximate length of 15km, width of 9km, and extend from depths from about
0.5m to at least 329m. Within the area drilled, host lithology sequences and brines show good continuity between drillholes. However, total porosity and the important specific yield porosity of the host
sequence lithologies have not been confirmed sufficiently at the current drillhole sampling.

Brine sampling and pumping tests indicate that two connected primary aquifers are at play in the salar, a middle aquifer within the volcanoclastic lithological units and an upper secondary porosity aquifer in the overlying halite evaposedimentary sequence. A lower aquifer in the sulfate – halite evaporite sequence also is projected to occur. Limited information is available upon which to support a reliable
characterization of this lower aquifer. However, this is anticipated to have much lower potential to be a productive aquifer.

Mining Method
Early phase hydrogeological tests in 2015, and current on-going long-term pump tests, indicate the brine extraction from the Salar de Llullaillaco will involve installing and operating a conventional brine production well field. The conceptual model for mineral recovery from brine reservoirs is a combination of brine extraction well field with brine pumped to a series of solar evaporation ponds and preliminary in-field brine treatment.

The production process starts when brine is pumped from the aquifer beneath the Salar, using electrical pumps, placed in bores (wells) that are completed in the Salar. The extracted brine is pumped from each well to a main distribution pipeline and then to the evaporation ponds.

Brine Well Field
Early phase hydrogeological tests in 2015, carried out at low, approximately 3 L/s pumping rates, concluded that pumping at rates greater than 97 L/s was not advisable, as drawdown at higher rates was estimated to be excessive and could potentially draw below the well filter. This was based on the upper aquifer limits and is therefore considered conservative. On-going pump test work, at higher pumping rates in the order of 60 L/s, indicate a similar to, or steeper, predicted flow rate to drawdown curves as the early tests. Given the final assessment of the on-going longterm pump tests is not finalized, the original interpolation has been used in the current conceptual design of the brine well field.

The conceptual approach to recovery of brine has focused on the use of two brine well fields, a smaller field in the west and a larger field in the central east region. The two locations for the proposed brine well fields were determined primarily based on the extent of the brine aquifer in the resource model, the ability to pump the brine aquifer at sufficient quantity and rate to support filling and maintaining levels of the evaporation ponds, and the brine lithium content. Pump tests, and samples collected, have shown only minimal variation in lithium concentration, indicating dilution of produced brine was not evident during the testing periods.

As a function of the lithium concentration (average Li = 306 mg/L) occurring naturally in the extracted brine, to supply a production line to ultimately produce sufficient concentrated brine to support an off-site 10,000 tonnes per year lithium carbonate plant, will require an average brine feed rate of 301 L/s. Seasonal variation in the evaporation rate is the major factor dictating the required brine flow rates to the evaporation ponds over the low of the winter months and peak high of the summer months.

For design of the required brine well field, the peak high flow of 473 L/s was selected. The drawdown predicted for 60 L/s, from the early work, was approximately 6 m. This was exceeded in the current testing at one site. The current testing has indicated a potential radius of influence (cone of depression/drawdown) of up to 1.5 km for pumping rates at near 60 L/s from one test site. To limit the drawdown and potential cumulative interference drawdown impact on the aquifer and salar hydrology environment, a conservative 30 L/s was used in the bore field design, and a broad bore spacing (1 km) was adopted. The predicted drawdown per bore at 30 L/s (108 m3 /hour), from the 2015 tests, is 2.2 m, or a standing water level (dynamic level) of 3m.

Subsequently, based on a high pump rate indicated by early testing and supported by ongoing pump testing at a rate of 30 L/s, it was estimated that there is a requirement for 16 bore holes, completed as brine extraction wells. Adopting a conservative approach, and to allow for rotation of the wells in the field due to maintenance and adaptive management strategy, 19 brine extraction wells have been planned for this conceptual stage.

A minimum of 16 brine production wells will be installed to meet the maximum brine feed rate of 473 L/s, with the installation of a maximum of 19 production wells to enable adaptive management. Well completion depths will vary and are still being studied; however, ongoing pump tests indicate the depths of the brine extraction wells could be up to 200 m.

Each brine production bore will be completed with 305 mm (12-inch) diameter stainless steel production casing and filter pipe and equipped with 380 V 203 mm to 254 mm (8 inch to 10 inch) submersible stainless steel pumping equipment. The pumping equipment is required to have capacity of 110 m3 /h and head coverage of 15–100 m. Power to each pump, and to the brine well field, will be delivered through a mid-range power line from a designated diesel power plant.

Extracted brine from the brine well field will be pumped to the evaporation ponds, where brine will be concentrated to a lithium saturation level of 4.70%.

The current brine well field design is conceptual in nature and subject to change, depending on factors such as logistics, economics, final outcomes of the current long-term pumping tests, as well as regulatory and socio-environmental considerations.

Raw Ore Stockpiling and Crushing
Leonite/schoenite, kainite and carnallite salts will be harvested by front end loader from the evaporation ponds and stored in three separate stockpiles adjacent to the processing plant. These salts will be reclaimed from each stockpile via a front-end loader and transferred to a hopper at a determined rate where they will be blended into a homogenous mixture. The blended salts will be withdrawn by a belt feeder and conveyed to a lump breaker to break any large agglomerates in the feed. Discharge from the lump breaker will be fed to the SOP process plant.

Slurrying, Scrubbing and First Conversion
After the lump breaker, the ore is fed to the slurry tank, where it is pulped with recycle brine. The resulted slurry will gravitate to the rod mill. The rod mill discharge is diluted with the recycle brine and screened. The screen oversize is recycled back to the rod mill. Screen undersize is fed to the conversion thickener. The thickener overflow brine is recycled, while the thickener underflow slurry is pumped to the conversion tank.

When the thickener underflow is mixed with the sulphate rich brine in the conversion tank, schoenite crystals are formed. The schoenite slurry is pumped to the acid conditioning tank (hydrochloric acid (HCl)) from the NaCl flotation circuit.

Solar Evaporation Ponds Process
To obtain concentrated brine with a Li concentration of 4.70% and solid products feeding the SOP production, several stages of solar evaporation and an intermediate stage of precipitation of magnesium and sulphate are used.

Extraction of Brine from Wells
The brine feed for the ponds is pumped from the deep brine extraction wells located within the Salar de Llullaillaco (the Salar) and transported by surface run pipelines to a series of solar evaporation ponds, which are also located within the Salar.

Solar Evaporation Ponds
The brine is pumped to the halite evaporation ponds (Ponds #1 and #2), which precipitate halite salts, leaving lithium (Li) concentrated in the brine. The lithium concentrated brine is then pumped to a series of kainite ponds (Ponds #3–#7), where schoenite/leonite and kainite are precipitated in each pond. The precipitated salts are harvested from the ponds using conventional earthwork equipment an ........