Larvotto Resources will shift to a dry tailing stacking process at its Hillgrove antimony-gold project in New South Wales after the State's planning and infrastructure department accepted a modification that offers a low-cost design and environmental benefits over typical wet storage.
Larvotto has also won approval to increase future throughput at the project to 500,000 tonnes per annum, which will likely increase the company’s annual production of antimony and gold.
Larvotto decided to move away from a conventional wet slurry tailings dam because the dry storage solution offered significant environmental and engineering benefits, given Hillgrove’s nature, scale and current infrastructure.
As a result of the switch, shorter environmental studies are now required, allowing the company to speed up the project's permitting process.
Dry stacking has gained momentum worldwide as a safer and more environmentally friendly process than wet storage of mine tailings, following the 2015 Mariana tailings dam collapse in Brazil. The collapse at the mine, owned by BHP, Vale and Samarco, caused extensive pollution along the Doce River. The companies were fined $45 billion to be paid over 20 years.
The dry stacking process starts with an initial filter press that extracts and reduces the water content to below nine per cent. The dried tailings are placed inside a plastic-lined containment area, where they are further compacted into a solid, stable mass.
When the stack reaches a certain height, a layer of topsoil is applied to maintain its structural integrity and allow revegetation and natural integration into the surrounding landscape.
Management says the dry stacking method has multiple other advantages over its less environmentally conscious alternative.
Traditional wet tailings dams can pose long-term stability risks and require extensive water management, while dry stacking minimises water runoff and blends the tailings into the terrain.
Dry tailings enable greater water recycling and recovery from processing operations. The method also requires less clearing per tonne of tailings, preserving the surrounding ecosystems.
To cap it off, the final structure isn’t classified as a dam, eliminating many regulatory and environmental concerns associated with conventional tailings storage.
Due to their stable landform, dry stacks pose fewer structural failure risks. This approach will allow Larvotto to begin rehabilitation earlier in the mining process, rather than waiting until completion, minimising long-term environmental impacts and improving its decommissioning plans.
Larvotto Resources managing director Ron Heeks said: “This is a great outcome for the project, ultimately enabling Larvotto to bring the Hillgrove antimony-gold project into production and become a globally significant antimony producer. Importantly, it is significantly more protective of the environment and enables resolution of legacy tailings issues, with no substantial change in project economics.”
The company says the projects economics will remain unaffected under the new plans as construction and operational costs are close to those of a conventional wet tailings dam.
If anything, dry stacking may save the company a few pennies since it avoids using the extensive pipelines and pumping infrastructure that would have been needed to move and store tailings at a proposed Clarks Gully tailings dam, five kilometres away from the Hillgrove processing plant.
Larvotto says it remains on track to deliver a definitive feasibility study, including the new dry tailings strategy, within the next six weeks.
In August, the company revealed a pre-feasibility study with compelling numbers, including an eye-bulging EBITDA of $652 million across a seven-year mine life from the production of 41,000 ounces of gold and 5400t of antimony per year, with a payback of just 14 months.
The pre-feasibility study numbers were based on conservative metal prices of US$2000 (A$3068) per gold ounce and US$15,000 (A$23,015) per tonne of antimony. Spot prices have since bolted to US$2890 per ounce (A$4540/ounce), with antimony soaring recently to more than US$35,000/t (A$55,000/t), suggesting a significant pop to the project economics is likely if the current prices are used.
The company's decision to switch its future waste storage to a dry stack solution appears to be a welcome step towards sustainable mining practices without compromising on efficiency or profitability.
With the global antimony supply deficit presenting a critical bottleneck in various industrial and defence applications, Larvotto's Hillgrove project appears well-positioned to become a key player in the market.
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By James Pearson
