The Taseko Mines story is indicative of the current environment miners find themselves in – maximise productivity to grow margins at existing operations or invest in innovative new methods of extracting critical metals that come with a reduced footprint.

The Vancouver-based company is pursuing both options at the two main assets on its books – the Gibraltar copper mine in British Columbia, Canada, and its Florence Copper project in Arizona, USA.

Gibraltar, owned 75% by Taseko, initially started up in 1972 as a 36,000 t/d operation. It was shut down in 1998 due to low copper prices before Taseko restarted it in 2004. In the years since, the company has invested over $800 million in the mine, increasing the throughput rate to 85,000 tons per day (77,111 t/d), where it’s been operating at since 2014.

The asset now sits as the second largest open-pit copper mine in Canada – with life of mine average annual production of 130 MIb (59,000 t) of copper and 2.5 MIb of molybdenum.

Stuart McDonald, President and CEO of the company, says the company continues to work on the trade-off of upping throughput – potentially past the nameplate capacity – and improving metallurgical recoveries at the operation.

This became apparent in the latest quarterly results, when Taseko reported an average daily throughput of 89,400 tons/d over the three-month period alongside “higher than normal” mining dilution.

The company believes Gibraltar can improve on both counts – mill throughput and mining dilution.

“We were optimistic coming into the new pit (Gibraltar Pit) that, based on the historical data, we could go above 85,000 tons/d as we got settled in and mined the softer ore,” McDonald told IM. “We still believe there are opportunities to go beyond that level, but, at some point, it becomes an optimisation and trade-off between throughput and recoveries.

“In our business, we’re not interested in maximising mill throughput; we’re interested in maximising copper production.”

On the dilution front, McDonald believes the problem will lessen as the mining moves to deeper benches in the Gibraltar Pit.

“As we go deeper, the ore continuity improves, so we hope the dilution effect will continue to improve too,” he said.

“The dilution rate is still not quite where we want it to be, so it’s a matter of looking at our operating practices carefully and following through a grade reconciliation process from our geological model through to assays from our blast holes, assays into the shovel bucket and all the way through to the mill.”

‘Assays into the shovel bucket’?

McDonald explained: “We do use ShovelSense® technology on two of our shovels, so that helps us assess the grade of the material in the shovel bucket.”

To this point, the company has leveraged most value from this XRF-based technology, developed by MineSense, when deployed on shovels situated in the boundaries between ore and waste. This offers the potential to reclassify material deemed to be ‘waste’ in the block model as ‘ore’ and vice versa, improving the grade of the material going to the mill and reducing processing of waste.

ShovelSense has been successful in carrying out this process with accuracy at other copper mines in British Columbia, including Teck Resources’ Highland Valley Copper operations and Copper Mountain Mining’s namesake operation.

McDonald concluded on this grade reconciliation process: “We just have to make sure we are tracing the material through all of those steps and not losing anything along the way. Gibraltar is a big earthmoving operation, so we must continue to keep the material flowing as well as look at the head grade.”

A different type of recovery

In Arizona at Florence Copper, Taseko has a different proposition on its hands.

Florence is a project that, when fully ramped up, could produce 40,000 t of high-quality copper cathode annually for the US domestic market.

It will do this by using a metal extraction and recovery method rarely seen in the copper space – in-situ recovery (ISR).

The planned ISR facility consists of an array of injection and recovery wells that will be used to inject a weak acid solution (raffinate – 99.5% water, 0.5% acid) into copper oxide ore and recover the copper-laden solution (pregnant leach solution) for processing into pure copper cathode sheets. The mine design is based on the use of five spot well patterns, with each pattern consisting of four extraction wells in a 100 ft (30.5 m) grid plus a central injection well. This mine outline and associated infrastructure comes with a modest capital expenditure figure of $230 million.

The company has been testing the ISR technology at Florence to ensure the recovery process works and the integrity of the wells remains intact.

Since acquiring Florence Copper in November 2014, Taseko has advanced the project through the permitting, construction and operating phase of the Phase 1 Production Test Facility (PTF). The PTF, a $25 million test facility, consists of 24 wells and the SX/EW plant. It commenced operations in December 2018.

Over the course of 18 months, Taseko evaluated the operational data, confirmed project economics and demonstrated the ability to produce high-quality copper cathode with stringent environmental guidelines at the PTF, the company says.

McDonald reflected: “We produced over 1 MIb [of copper] over this timeframe and then switched over from a copper production cycle into testing our ability to rinse the orebody and restore the mining area back to the permitted conditions.

“We’re proving our ability to do the mining and the reclamation, which we think is a critical de-risking step for the project.”

Taseko says Florence Copper is expected to have the lowest energy and greenhouse gas-intensity (GHG) of any copper producer in North America, with McDonald saying the operation’s carbon footprint will mostly be tied to the electricity consumption required.

“Our base case is to use electricity from the Arizona grid, which has a combination of renewables, nuclear and gas-fired power plants,” he said. “In the longer-term, there are opportunities at Florence to switch to completely 100% renewable sources, with the most likely candidate being solar power.

“At that point, with renewable energy powering our plant, we could be producing a copper product with close to zero carbon associated with it.”

Gibraltar has also been labelled as a “low carbon intensity operation” by Skarn Associates who, in a 2020 report, said the operation ranked in the lowest quartile compared with other copper mines throughout the world when it comes to Scope 1 and 2 emissions.

When it comes to the question of when Florence could start producing, Taseko is able to reflect on recent successful permitting activities.

In December 2020, the company received the Aquifer Protection Permit from the Arizona Department of Environmental Quality, with the only other permit required prior to construction being the Underground Injection Control (UIC) permit from the US Environmental Protection Agency (EPA).

On September 29, the EPA concluded its public comment period on the draft UIC it issued following a virtual public hearing that, according to Taseko, demonstrated strong support for the Florence Copper project among local residents, business organisations, community leaders and state-wide organisations. Taseko says it has reviewed all the submitted comments and is confident they will be fully addressed by the EPA during its review, prior to issuing the final UIC permit.

Future improvements

In tandem with its focus on permitting and construction at Florence, and upping performance at Gibraltar, the company has longer-term aims for its operations.

For instance, the inclusion of more renewables to get Florence’s copper production to carbon-neutral status could allow the company to benefit from an expected uptick in demand for a product with such credentials. If the demand side requirements for copper continue to evolve in the expected manner, it is easy to see Taseko receiving a premium for its low- or no-carbon product over the 20-year mine life.

At Gibraltar, it is also pursuing a copper cathode strategy that could lead to the re-start of its SX-EW plant. In the past, this facility processed leachate from oxide waste dumps at the operation.

“As we get into 2024, we see some additional oxide ore coming out of the Connector Pit, which gives us the opportunity to restart that leach operation and have some additional pounds coming out of the mine,” McDonald said.

Alongside this, the company is thinking about leaching other ore types at Gibraltar.

“There are new technologies coming to the market in terms of providing mines with the opportunity to leach sulphides as well as oxides,” McDonald said. “We’re in the early stages of that work, but we have lots of waste rock at the property and, if there is a potential revenue stream for it, we will look at leveraging that.”