Soil with minerals

By Rebecca Todesco, Editor, Mining Magazine

As the green energy transition ramps up, demand for the minerals that will drive the transformation, like lithium, shows no signs of slowing down. With this skyrocketing demand comes the need for a better understanding of lithium deposit concentration and distribution across Australia.

Lithium has been recognised as a critical mineral by countries across the world, including Australia, Japan, Canada, and the US. With the essential role it plays in the sustainable clean energy future, Australia is well positioned to capitalise on its position as a global leader in lithium supply.

Despite this advantageous position, comprehensive investigation into spodumene-similar deposits across Australia has yet to be executed. Without this kind of in-depth investigation, the immediate expansion of Australia’s lithium industry would be difficult.

The absence of this knowledge is a gap that a team of researchers from the University of Sydney, led by Dr Wartini Ng, attempted to fill, working to complete the first digital map of lithium content in Australian soil.

“There has been an ongoing demand for lithium – the primary raw material for batteries which can be used in electric vehicles worldwide,” Dr Ng said.

“As one of the largest producers of lithium, we aim to delineate potential anomalous areas of lithium within Australia.”

The University of Sydney research team utilised a method known as digital soil mapping to carry out their study. Also known as predictive soil mapping, digital soil mapping is the computer-assisted creation of digital maps of soil properties and soil types.

“Digital soil mapping is a methodology tocreate digital maps of soil attributes across a landscape by coupling the soil attributes of interest (could be either laboratory or field measurement) with spatial earth observations (satellite- sensed) data using machine learning models,” Dr Ng said.

“We know that the formation of soil is affected by key factors, including climate, organisms, topography, parent material, and age.

“For this study, we mapped the concentration of lithium in soils, which is commonly found in mineral deposits such as spodumene.”

Soil samplesLooking for lithium

Dr Ng said the lithium content in soil is affected by environmental conditions that drive the mineralisation process, including elevation, slope, precipitation and other geochemical variations.

The digital soil mapping framework, usually used for spatial soil analysis, remained the same throughout the study, with the research team simply choosing the target soil attribute of interest, that is, lithium concentrations collected from the National Geochemical Survey of Australia (NGSA) project.

“We used a range of earth observation data that we know correlates well with soil, in particular, the barest earth image of the Australian continent, which revealed the surface of the soil.”

Dr Ng said that to conduct the study the team trained a machine learning model with the lithium concentration from the NGSA survey as a target.

“The model simply learned how lithium concentration varies from site to site as defined by their environment. By learning this pattern, the model can predict lithium concentration throughout Australia.”

Predicted spatial distributions of aqua-regia-soluble Li (mg kg−1) in alluvial soils across Australia for both top outlet sediment (TOS) 0–10 cm and bottom outlet sediment (BOS) depth ∼ 60–80 cm

Analysing the results

The goal of the research team was to create a digital map of lithium content in Australian soil, and they did.

“In this study, we generated the first digital soil map of lithium in Australia. The predicted lithium maps correlated well with the current existing lithium mines and identified several potentially anomalous lithium areas that had yet to be verified, in which ground-truthing is required.”

In the past the lithium exploration taking place in Australia has been primarily focused in Western Australia, but the team’s lithium map indicates other regions in Australia that are anomalous in lithium.

The study and the resulting map of lithium distribution suggests that although the highest lithium concentrations are located near the Greenbushes deposit, as well as near Mount Marion and Earl Grey in Western Australia, elevated concentration of lithium in Queensland, southern New South Wales and parts of Victoria indicate that other locations may have a potential role to play in Australia meeting future lithium demand.

Looking towards the future

“This is the first study in which we apply the digital soil mapping methodology for critical minerals. Anomalous lithium concentrations do not translate to exploration targets but we hope to trigger further detailed work using our approach,” Dr Ng said.

Despite the low prediction accuracy, Dr Ng said that the team’s work paves the way for the development of digital maps for other geochemical elements.

The report published by the team post-study acknowledges that the map is not conclusive, stating that “the model performance was on the low side and inclusion of the results into a prospectivity framework needs to consider the model uncertainties”.

As well as being the first step towards creating digital maps for other geochemical elements, the map offers a good starting point for lithium companies hoping to broaden their prospects to look into further investigation and exploration.

“The industry could potentially explore the identified elevated areas for ground- truthing and identify suitable areas to mine and increase the amount of lithium produced in Australia in its ongoing effort of global energy transition,” Dr Ng said.

“This work provides a framework to better understand the process controlling soil lithium concentration and the modeling work effectively delineates regions with locally higher lithium source potential. This approach could be used for future prospecting.”

 

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