Potassium is a critical nutrient for plant growth and vital for agriculture. Potash deposits are the primary source of potassium. Although stratabound potash deposits provide the majority of the world’s potash, potassium-enriched brines contain the most widely defined and in-development potash resources in Western Australia. Here, potash evaporites are obtained via the evaporation of potassium-enriched brines in the mining process.

In contrast to most global potash production, which is from ‘hard rock’ stratabound sources, potash can be extracted from brine or brine-related processes such as evaporation of inland and seawater derived brines, or the extraction of alunitic clays from acidic salt lake environments. The focus of this system is on the formation of inland potassium enriched brines that are near the surface within salt lakes, playas or paleovalleys. These brines form the resource for extraction of potash via onsite evaporation in the mining process. Compared with other forms of potash mining, this method has the disadvantages of relying on climate for evaporation and requiring larger tracts of land for extraction and evaporation operations. However, this method has a significant advantage in the economic production of SOP due to the chemistry of the brines, specifically the presence of sulfate. Along an evaporation circuit, halite will precipitate first leaving behind a brine enriched in potassium and sulfate, from which potassium sulfate minerals such as kainite (KMgSO₄Cl·3H₂O) and schoenite (K₂Mg(SO₄)₂·6H₂O) can be precipitated (Salt Lake Potash Ltd, 2016).

Within Western Australia, the evaporite brine-related potash mineral system is associated with inland salt lakes, playas and paleovalleys. In this system, the potassium is predominantly sourced from the dissolution of potassium bearing minerals from the surrounding lithologies, then transported along surface and groundwater pathways with the source of the water flux being rainfall or groundwater (English et al., 2012; Border and Sawyer, 2014). Potassium is then concentrated in salt lakes, playas or paleovalleys, either as soluble minerals or within brines of neutral to high pH.

Derived layers are grouped based on their critical features:

SOURCE – scavenging of potassium from country rocks by meteoric waters

PATHWAY – transportation of potassium-bearing fluids from source to trap, predominantly by groundwater systems

TRAP – formation of potassium-enriched brine pools in salt lakes, playas and paleovalleys, mainly via evaporative discharge

The Mineral System Tree is the graphical display of a mineral systems analysis showing the link between critical/constituent processes and their recommended targeting features and GIS layers.

 Mineral System Tree: Evaporite brine-related potash

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