Characterizing Lithium Enriched Brines As Mineral Resources and Reserves

Unlike traditional mineral resources that are solid deposits, brine mineral resources are fluid deposits of variable density and mobility.  As an example, lithium enriched brines are hosted in porous- and fractured-rock aquifers, typically within closed hydrologic basins (salars).  Compared to hard rock deposits, the variable density and mobility of these brine deposits present challenges with respect to exploration, characterization, and quantification. The conceptualization and exploration of brine mineral resources, the mining plan, and definition of the mineral reserve for each deposit require not only an understanding of the spatial and temporal variability of brine densities and concentrations, but also the variability of the flow characteristics in the aquifer where the brine is stored.

As outlined by standards and guidelines for quantifying mineral resources and reserves, key variables such as brine volume and grade, aquifer geometry, hydrogeologic unit, effective porosity, specific yield, flow rate, and recoverability are used in order to meet the definition of reasonable prospects of economic extraction and to define the mineral resource.  Conversion of status from a mineral resource to a mineral reserve requires modifying factors ranging from mining methods, to processing strategies, to environmental, social, and permitting aspects of the project.  

Production wells in deeper deposits, or extraction trenches for shallower systems, are generally the mining methods for extraction of brine resources.  Hydrogeologic methods are thus critical to evaluating what portion of a defined mineral resource is economically extractable and can in turn be defined as a mineral reserve.  Consistent with industry guidelines, we use the technical reporting terms “Drainable” and “Extractable” as factors for evaluating and advancing project status from mineral resource to mineral reserve. These hydrogeologic modifying factors are in part supported using exploration results, aquifer testing, conceptual modeling, and hydrodynamic numerical modeling methods simulating wellfield or trench extraction for mining the lithium-enriched brine.