Demand for lithium, a key battery metal, is on the up. The largest brine (Salar de Atacama, Chile) and pegmatite (Greenbushes, Western Australia) lithium producers have been working up to double their production capacity to take up the slack in the short term, but that may not be enough to meet demand in the 2030s and beyond. Novel sources could help plug the gap – enter lithium clays.
These are sedimentary deposits where lithium is bound within clay minerals. While there are currently no lithium clay deposits in production, interest is ramping up, particularly in the USA where there is a push to find home-grown sources of the critical mineral.
The host rocks are varied and in SRK’s experience include clay-altered ash tuffs, carbonate marls or carbonaceous siltstones. Common features are a lacustrine depositional setting and an association with rhyolite volcanism. The genetic model is still up for debate – low-temperature hydrothermal or hot-spring alteration of permeable basin sediments, diagenesis of fine-grained deposits containing lithium-rich ash or glass components, or a mixture of both? Faults are important, both as conduits for lithium-bearing fluids and by forming distinct fault-bound basins each having unique internal stratigraphy. Ultimately, the lithium content is controlled by underlying changes in the physical and chemical characteristics of the volcanic or sedimentary host; therefore, patterns in grade often closely reflect changes in internal stratigraphy.
The majority of lithium clay deposits benefit from being near surface, generally flat-lying, and having simple stratigraphy. They are also much softer than their hard-rock pegmatite cousins. This should facilitate mining with very low strip ratios and removes the need for expensive drilling and blasting during extraction. If the clay mineralogy is favourable (illite clays as opposed to smectite clays) we can also remove energy-intensive roasting from the processing (unlike the pegmatite deposits which need to break down spodumene through calcination).
While these clay deposits have the potential to be large – the top three lithium clay deposits in the Americas, Sonora (Mexico), Thacker Pass (Nevada), and Clayton Valley (Nevada) – each have contained lithium carbonate equivalent (LCE) resources similar to or larger than the Greenbushes pegmatite project (at least 7 Mt LCE) - they are generally lower grade. As such they may require proportionally large quantities of reagents to effectively leach and recover lithium. Similar to brines, the devil is in the detail – sediment chemistry, the types of clay species present, and the relative proportion of impurities, all have an impact and are unique to each deposit. To exploit lithium clays effectively, coming up with novel processing flowsheets is both an opportunity and necessity.
