The Evaluation of Brine Prospects and the Requirement for Modifications to Filing Standards

Abstract

The recent increase in demand for lithium has lead to the development of new brine prospects, particularly in the central Andes. The brines are hosted in closed basin aquifers of two types: mature, halite dominant, and immature, clastic dominant. The estimation of elemental resources in these salars depends on a detailed knowledge of aquifer geometry, porosity and brine grade.The geometry of the aquifers can be evaluated by classical geophysical and drilling techniques, but since the resource is a fluid, with the attendant problems of in-aquifer mixing and dilution, existing codes for filing resource and reserve estimates need modification. Total porosity is 2 relatively straightforward to measure, but effective porosity and specific yield, which are required to estimate the resource, are rather more difficult. Recovery factors are low compared with metalliferous and industrial mineral deposits due to reliance on pumping for extraction.These and related issues are discussed in-depth, and suggestions for changes to the reporting of resources and reserves are put forward for such brine prospects.

Regional groundwater flow and accumulation of a massive evaporite deposit at the margin of the Chilean Altiplano

“…Irrespective of mechanistic reasons, the time discontinuity of many millions of years between the older deposits and Unit M implies a different set of boundary conditions. Considering surficial halite porosity (10%) [Houston et al, 2011], the nucleus aquifer surface area (1660 km 2 ) and thickness (40 m), and 100,000 mg/L Na in brine, the nucleus brine alone hosts 6.6 × 10 11 kg of Na. Based on core data, we estimate that halite composes 90% of the nucleus and 25% of transition zone.…”

“…Because there is almost no porosity below 40 m [Houston et al, 2011], Na in brine below this depth is assumed to be negligible. We add estimated Na in brine in the productive nucleus aquifer (upper~40 m) to Na in halite to constrain total Na accumulated since 10 Ma.…”

“…ET at the elevation of the salar varies between 0 and 2.8 mm/d depending on the land surface characteristics [Kampf and Tyler, 2006]. Evaporation rates exponentially decline below the land surface to near zero by 2 m depth [Houston et al, 2011]. The halite nucleus is bordered by a transition zone where sulphate, carbonate, and diatomaceous deposits interfinger with siliciclastic alluvium and volcanic deposits.…”

Lithium availability and future production outlooks

“…However, brine -presently the main lithium source -is a fluid and commonly used definitions can be difficult to apply due to pumping complications and varying concentrations. Houston et al [35] describes the problem in detail and suggest a change in NI 43-101 to account for these problems. If better standards were available for brines then estimations could be more reliable and accurate, as discussed in Kushnir and Sandén [18].…”

Global Lithium Resources and Sustainability Issues

“…In the case of lithium, Yaksic and Tilton 48 estimate that, in average, 45% of the Li contained in brines and 50% of the Li contained in pegmatites, hectorite, or jadarite deposits are actually recoverable. In their recent paper, Houston et al 51 discuss in detail the intricacies of evaluating the recoverable fraction of a salt lake Li resource, stating the following: "Once well inefficiency, drawdown limitations, possible barren inflows and economics are entered into the equation, extraction of more than 33% is only possible under exceptional circumstances." When counting for further losses occurring in the production of the high-purity lithium carbonate or hydroxide needed by the Li-ion, this figure may drop to about 25% of the resources.…”