Hudbay Minerals has one of the lowest cost per tonne copper sulphide operations in Peru on its hands at Constancia, but it is intent on continuously improving the mine’s margins and environmental performance through a commitment to continuous improvement. This has recently led it to exploring the potential of sensor-based ore sorting.

Hudbay’s operations at Constancia include the Constancia and Pampacancha pits, an 86,000 t/d ore processing plant, a waste rock facility, a tailings management facility and other ancillary facilities that support the operations.

The company increased reserves at the mine, located in the Cusco department, by 33 Mt at a grade of 0.48% Cu and 0.115 g/t Au last year – an increase of approximately 11% in contained copper and 12% in contained gold over the prior year’s reserves.

With the incorporation of Pampacancha and Constancia North, annual production at Constancia is expected to average approximately 102,000 t of copper and 58,000 oz of gold from 2021 to 2028, an increase of 40% and 367%, respectively, from 2020 levels, which were partially impacted by an eight-week temporary mine interruption related to a government-declared state of emergency.

Constancia now has a 16-year mine life (to 2037) ahead of it, but the company thinks there is a lot more value it can leverage from this long-life asset and it has been looking at incorporating the latest technology to prove this.

In recent years it has, for instance, worked with Metso Outotec to improve rougher flotation performance at Constancia using Center Launders in four e300 TankCells and installed a private LTE network to digitise and modernise its open-pit operations.

Peter Amelunxen, Vice President of Technical Services at Hudbay, said the Constancia ore sorting project – which has seen Hudbay partner with MineSense on a plan to trial the Vancouver-based cleantech company’s ShovelSense X-ray Fluorescence (XRF)-based sorting technology – was one of many initiatives underway to further improve the operating efficiency at Constancia.

“The ore sorting program is separate from the recovery uplift program at Constancia,” Amelunxen said, referring to a “potentially high-return, low capital opportunity” that could boost milled copper recovery by 2-3%.

He added: “The ore sorting program is expected to yield positive results at the mining phase of the operation and is expected to increase the mill head grade and reduce metal loss to the waste rock storage facility.”

Back in April 2021 during a virtual site visit, Hudbay revealed it was trialling bulk sorting at Constancia as one of its “optimisation opportunities”, with Amelunxen updating IM in mid-January on progress.

Hudbay has previously evaluated particle sorting at its Snow Lake operations in Manitoba – with the benefits outlined in a desktop study “muted” given “bottlenecks and constraints”, Amelunxen said – but, at Constancia, it considered XRF sorting from the onset for copper-grade only pre-concentration, due to its perception that this application came with the lowest potential risk and highest probability of success.

The company has a three-phase evaluation process running to prove this, with phase one involving a “bulk sorting amenability study”, phase two moving up to laboratory-scale testing and phase three seeing trials in the field.

The “bulk sorting amenability study” looked at downhole grade heterogeneity to estimate curves of sortability versus unit volume, Amelunxen detailed. Laboratory testing of drill core samples to evaluate the sensor effectiveness was then carried out before an economic analysis and long-range-plan modelling was conducted.

With the concept and application of bulk sorting having cleared all these stage gates, Hudbay, in November, started pilot testing of XRF sensors on a loader. This involved fitting a ShovelSense unit onto the 19 cu.m bucket of a Cat 994H wheel loader, with around 20 small stockpiles of “known grades” loaded onto the bucket and dispatched into a feeder and sampling system (pictured below, credit: Engels Trejo, Manager Technical Services, Hudbay Peru). With this process completed, the company is now awaiting the results.

At a similar time, the company moved onto demonstration trials of a “production” ShovelSense sensor unit on the 27 cu.m bucket of a Hitachi ECX5600-6 shovel operating in one of the pits. It has collected the raw spectral data coming off this unit since the end of November, with plans to keep receiving and analysing sensor data through to next month.

“We should have the finalised XRF calibration in February, at which time we’ll process the raw data collected during the three-month trial period and compare it with the short-term mine plan (ie grades of ore shipped),” Amelunxen said. “So, by the end of February or early March, we’ll be able to validate or finetune the economic model.”

Should the results look favourable, Amelunxen is confident that leasing additional sensors and installing them on the other two Hitachi ECX5600-6 shovels will not take long.

“Plans may change somewhat as the program unfolds,” he said. “For example, we may have success sorting ore, but feel additional calibration is required for waste sorting at Pampacancha, in which case we may install production sensors on Constancia ores while doing another trial program at Pampacancha.

“It all depends on the precision of the XRF calibration.”

Higher head grades and potentially higher copper recoveries may be the headline benefits of using ore sorting technology, but Hudbay is equally focused on obtaining several key environmental benefits, including reduced consumption of energy and water.

On the latter, Amelunxen said: “This is expected due to the processing of less ‘waste’ by removing uneconomic material earlier in the process and reducing the hauling and processing costs of the uneconomic material.”

Looking even further forward – past a potential commercial implementation of XRF-based ore sorting at Constancia – the company plans to evaluate the application of other sensors, too.

“For our future development copper project in Arizona, we plan to look at other sensors as well,” Amelunxen said, referencing the company’s Rosemont asset.

This ore sorting project is not the only project the processing team at Constancia are examining, as Amelunxen already hinted at.

As part of the recovery uplift project, it is installing equipment that will allow the operation to increase the overall mass recovery of the roughers, which is currently constrained by the downstream pumps and cleaning circuit.

“This will allow us to achieve an expected 2-3% increase in copper recoveries without impacting concentrate grade,” Amelunxen said.

It has various initiatives underway under the “Moly plant improvement projects” banner, too. This includes flowsheet optimisation, pH control in the cleaners and pH reduction in the bulk cleaners.

“This project has been in the works since late 2019, and the new mechanical agitator installation in the cleaning cells was completed during the August 2021 schedule mill maintenance shutdown and the new nitrogen plant was commissioned in the second half of the year,” Amelunxen explained. “The next steps are pH control in the cleaners (with CO2), water balance optimisation and potentially installing a Jameson flotation cell as a pre-rougher (the cell is already on site and not in use, it will be repurposed pending results of the pH trials).”

A flotation reagent optimisation study is also on the cards, aimed at reducing zinc and lead contamination in the copper concentrate.

“A depressant addition system is on the way to site and should be installed in February, with plant trials commencing in March,” Amelunxen said, explaining that this followed laboratory test work completed in 2021.