Underground leaching method reduces costs and rock movement, unlocking low-grade copper with in-place recovery and advanced blasting

The pursuit of critical minerals is pushing miners deeper underground, where innovation—not just excavation—is becoming the key to unlocking value.

In a standout presentation at the AusIMM Underground Operators Conference 2025 in Adelaide, Dr Armineh Hassanvand, senior research engineer at Orica, unveiled a groundbreaking collaborative effort to assess the viability of In-Place Recovery (IPR)—a novel underground leaching method that could redefine how low-grade hard rock copper deposits are exploited.

“If you see the word ‘innovation,’ it means be patient,” Dr Hassanvand told delegates. This is about exploring a new mining method—one that no one has approached in such a systematic and staged way before.

Rethinking the Underground Process

Traditional underground mining methods, such as sublevel open stoping, involve drilling, blasting, hauling ore to surface, and processing it through energy-intensive milling and smelting operations. In contrast, IPR offers a radically different approach: blast the orebody, but leave it in place. Inject a leaching solution from the top of the stope, let it percolate through the fragmented rock, and pump the dissolved metals to the surface to produce copper cathodes.

This is not in-situ recovery (ISR), which relies on natural rock permeability and is common in uranium operations. Nor is it heap leaching, where ore is extracted, crushed, and irrigated on surface pads. Instead, IPR adapts principles of both, engineered specifically for hard rock formations lacking natural permeability.

“If you don’t blast it, you don’t have enough fractures for solution to flow,” Dr Hassanvand said. “The goal is to generate a permeable structure inside the orebody, then use leach chemistry to extract the metal with minimal surface disruption.”

Making the Case: Economic and Environmental

IPR’s strongest argument may lie in its economic and sustainability credentials. A financial modelling comparison between a hypothetical sublevel open stope operation and an IPR equivalent—both producing 50 ktpa of copper—showed a 25 percent reduction in opex and significant capex savings for the IPR case, even with lower assumed recovery.

“Hydrometallurgical plants are cheaper to build than pyro plants, and if we can access previously untouched low-grade zones around high-grade stopes, that’s additional upside,” Dr Hassanvand said.

Crucially, this aligns with decarbonisation and ESG objectives: less material movement, less energy, and smaller environmental footprints. In some jurisdictions, these benefits could be the difference between project approval and rejection.

Backed by Industry and Government

This isn’t just theory. Orica is leading a CRC-P-funded initiative alongside BHP, Core Resources, and The University of Adelaide. The trial will take place at BHP’s Prominent Hill mine in South Australia, in a sub-economic test area of the Ankata region, chosen specifically to avoid interfering with ongoing production.

“We want to build confidence in a staged approach,” Dr Hassanvand explained. “For the initial trial, we’ll use water and tracers—no reagents—so we can study the effects of blasting  on permeability and flow characteristics without chemical risk.”

Core Resources is conducting lab-scale leach testing; the University of Adelaide is building a multi-physics simulation model; and Orica is optimising blast designs using advanced fragmentation models.

The Science of Fragmentation

Blasting isn’t just about rock breakage in IPR—it’s about precision-engineered blasting to maximise leach performance Using Orica’s numerical fragmentation model, the team is simulating the impact  of various ring designs, including different explosive energies, blasthole diameters and burden-to-spacing ratios.

“We’ve gone from P80 of 178 mm down to 69 mm,” said Dr Hassanvand, referring to particle size after blasting. “That’s a 60 percent reduction. But remember, surface area increases with the square of the diameter—so the gain in reactive surface is massive.”

Unlike heap leaching, which can engineer particle size through crushing, IPR must work with the outcome of real blasts as the sole rock conditioning stage. Creating a more uniform and optimally sized fragment distribution in the stope is, therefore, essential.

Fluid Flow and Leach Chemistry

The leach experiments in the lab target secondary copper sulphides like chalcocite and covellite—more challenging than oxides, but more realistic in the current geological context. Ferric sulphate is the primary oxidant under study.

“We didn’t want to ‘cheat’ with oxides,” Dr Hassanvand said. “Those are already mined out in most deposits. We’re looking at what’s really left—low-grade sulphides.”

At the same time, the University of Adelaide team is simulating the coupled behaviour of flow, saturation, heat transfer, and chemical reactions within packed rock fragments. These models are calibrated with lab data and will be validated against the field trial data.

“It’s a powerful tool,” Dr Hassanvand noted. “We can simulate what happens after a few hours, a few weeks, a year. You can see where saturation is high, where flow slows, and  estimate achievable copper recovery under each scenario.”

A Modular, Scalable Vision

The end game is to produce a digital simulator that enables mine planners to evaluate IPR for any given stope.

“Eventually, a mine will be able to say, ‘Here’s my geology, here’s my stope—can I use IPR?’ And we’ll be able to model it without running a full field trial first,” she said.

This would not only accelerate adoption but reduce risk and capital outlay—particularly attractive to mid-tier and brownfield operators seeking new life from existing infrastructure.

Perfect Fit for Remnant Mining

During the Q&A session, Dr Hassanvand was asked whether IPR could be applied to remnant ore zones and old workings.

“If you know one, please reach out!” she said. “Some mines have left behind fairly high-grade ore. Sometimes they’re shallow, too—which is even better. And if they have ESG or licence challenges, IPR could be a very attractive solution.”

A Strategic Shift, Not Just a Technical One

IPR is more than an innovation—it’s a philosophical shift. It challenges the assumption that ore must be hauled, crushed, and milled. And it could help mining companies align with long-term sustainability goals while cutting costs and unlocking new resources.

Or as Dr Hassanvand concluded:

“We’re not just asking whether it works—we’re building the evidence to show that it can work economically, safely, and sustainably. And that’s how new mining methods begin.”

Picture: Dr Armineh Hassanvand presents Orica’s collaborative research into In-Place Recovery (IPR), showcasing a novel underground leaching method for low-grade copper extraction. Photo: Jamie Wade.