A future in which energy and material movement conservation in mining is paramount would seem to have a spot reserved for in-place recovery if the right answers can be found to some key questions. Industry heavyweights such as BHP and Orica have decided the time is right to press for answers.
Advancing technology and technical capability in vital areas have conspired to help their cause. A massive plus, though, is the availability of a zone within BHP’s mature Prominent Hill copper-gold operation in South Australia for important IPR field testing.
Orica senior research engineer Armineh Hassanvand said at this month’s 2025 AusIMM Underground Operators Conference in Adelaide the in-field trial was a critical step toward scaling up to a full-blown IPR operation.
Bench-scale hydrometallurgical testwork was helping to refine the partners’ understanding of leaching kinetics of copper sulphide samples from Prominent Hill. The benchtop testing also achieved a circa-65% copper extraction rate from ground rock which showed that, despite being challenging, copper recovery from the sulphide ores was achievable.
Other high-level modelling has pointed to the economic viability of IPR given certain constraints. Demonstrating the technical viability required lots of real-world assessment. And extensive collaboration.
“There is mining, there is leaching and metallurgy, there is blasting [and] there is modelling involved, so it was not a question for us to tackle individually at Orica,” Hassanvand said.
“BHP and Prominent Hill are playing a pivotal role.
“Core Resources is … providing metallurgical test services. Modelling experts at the University of Adelaide are developing a multi-physics tool.
“When you think about stope leaching you’re going from blasting to processing so blasting has a key role here. You need to get to the optimum smallest particle size you can, safely, to maximise the recovery. And that’s the role Orica is playing.”
A conference paper co-authored by Hassanvand, Core Resources’ senior metallurgist David Hunter, University of Adelaide PhD Zhihe Wang and BHP innovation lead, Andrew Scott, outlined the attractions of IPR, which combines elements of block caving, insitu recovery (ISR), stope drilling and blasting, and surface heap leaching. Instead of injecting a solution into a permeable ore deposit to capture and recover a mineral-pregnant liquid, IPR has lixiviant percolating through a blasted underground rock mass to deliver solution for transfer to the surface for processing.
Mineral recoveries are expected to be lower for the underground hard-rock leaching method versus ISR but the returns will be additive to other forms of production.
“Early adoption of the method will likely be as a hybrid approach where high-grade ore is mined conventionally and adjacent low-grade ore is recovered through IPR,” Hassanvand said.
“We’ve been allocated an area [at Prominent Hill] that is sub-economic, which [is] … not representative of the Prominent Hill reserve. The advantage of that is that we have minimum interruption to day-to-day production.
“For this very first trial and demonstration we decided to have the extraction and the leaching aspects of it [be] done ex-situ, which means out of the underground environment, and limit the trial to use of water and water traces.
“This will allow us to investigate the effects of fragmentation and permeability and gain a lot more confidence and introduce this concept in a staged approach to be able to manage the risk.
“Core Resources has received samples from the site and they have been going through a very typical hydrometallurgical test regime.”
While chalcopyrite, chalcocite and bornite copper-bearing minerals are the focus at Prominent Hill, Hassanvand said it was felt that IPR as a “down-the-track” production option was best aimed at secondary copper sulphides such as chalcocite and covellite. The chemical engineer said laboratory assessment of ferric, or iron, sulphate as an oxidising agent that could remove copper and bring it into solution was advancing. “We are assessing different concentrations of acid, pH, temperature,” she said. “When it comes to adding these reagents … it’s not always the more the better. There’s always a sweet spot that we need to find for each ore and that is what makes the lab process quite time consuming.
“We are hoping to gain knowledge at lab scale and build a model robust enough to forecast this performance rather than every time going through a lab testing process.”
Equally calculative is work on blast design and stope fragmentation. Orica these days brings an extensive suite of blast control, monitoring and modelling tools to the table and these are being used to continually optimise muckpile materials for efficient loading and hauling in metalliferous mines.
“When it comes to stope leaching it’s [cost-effective results] greatly dependent on the particle size that you have left in the stope and that’s the role that blasting is playing,” Hassanvand said.
“We have been able to use Orica’s numerical fragmentation model … [to assess] explosive detonation performance and all the rock mass properties – elastic, plastic, structural, in-situ – combine them all, and see what sort of particle size we are generating out of a blast.”
Modelling by the University of Adelaide’s Wang took this work to another level.
“He’s helping us with building a model, which I refer to as multi-physics … because we are solving different physics simultaneously,” Hassanvand said.
“We are looking at fluid flow, mass transfer, reaction [and] heat transfer, coupled together. And if you want the model to be representative you need to look at the model at different scales … to understand how IPR behaves.
“Anyone who is familiar with [this type of] modelling work can tell you modelling a 30m-to-50m stope at the micrometre level of resolution is quite computationally demanding.
“We have tackled this by focusing and interrogating at that grain size, then generalising with making a bigger unit and then building up on that. Currently we are running stope-scale modelling at a very reasonable time frame and getting very exciting results.”
The partners’ hydro-thermo-chemical fluid flow multi-scale modelling will continue to advance as it is fed increasingly with real-world data, according to Hassanvand.
“Ultimately we would like to have this simulator tool that can bring leaching data into it, blast fragmentation and heave modelling into it and also site data … and [can] simulate IPR so that mine sites can come to us and say, I have this stope, is it feasible to get money out of it with IPR?
“We would be able to use the simulator to answer that question before going to work, saving a lot of lab and field trials,” she said.
