Freeport-McMoRan discovers large sulphide copper reserves and restores milling operations adding energy-efficient capacity
By Steve Fiscor, Editor-in-Chief
Few American mines have a history and a deposit as rich as Freeport-McMoRan’s Morenci mine. Located in the mountains of southeast Arizona, copper has been mined in this district for nearly 150 years. Ironically, at a time when most copper mines are seeing ore grades and reserves dwindle, and new copper discoveries are rare, Morenci has found a large primary sulphide deposit below its existing operations and increased its copper production.
Generations of copper miners have cut their teeth at Morenci. The copper ore that attracted the first miners was rich by today’s standards (15% copper). As the high grade ore disappeared on the surface, the miners ventured underground. Picks and shovels were eventually replaced by mechanical equipment and large scale open-pit operations. For much of the 20th century, Morenci was one of the world’s major copper mining operations.
More recently, the mine managed to survive the historically low copper prices of the late 1990s by transitioning to heap-leach techniques, which allows copper extraction from low-grade oxide and secondary sulphide ores. The milling operations were idled as the mine pursued leachable ore. Flotation gave way to solvent extraction.
In 2007, Freeport-McMoRan became the owner of the property when it purchased Phelps Dodge. Viewing Morenci with fresh eyes, better copper prices and deeper pockets, Freeport saw an opportunity. The company embarked on an exploration drilling campaign and proved up one of the largest porphyry copper systems ever discovered. Morenci now had more copper in reserves and mineralized material (25 billion lb) than had been mined throughout its history to date. It also had unused permitted milling capacity and a workforce with a can-do attitude.
Deciding to strike while the iron was hot, the company fast-tracked expansion plans incorporating untested, energy-efficient technology they had helped develop. They moved forward quickly with both engineering and construction. “The way we all worked together safely to make this thing happen—that’s what gets me excited about the Morenci project,” said Red Conger, president, Freeport-McMoRan Americas. “The way we responded to the challenges is what separates our company from others. We brought a lot of different resources to bear on this. And, the technology we have implemented will have a positive impact on future concentrator designs.”
From concept to commercial production, 2009-2014, 4.5 years is relatively quick considering the timeline of similar projects. In the process of unlocking this property, they not only boosted production at a mature copper mining complex, they reinvigorated a mining community and reaffirmed something they knew all along—they are some of the best copper miners in the world.
The Decision to Restore Milling Operations
To date, Freeport has invested more than $1.6 billion to expand production at Morenci to more than 1 billion lb per year (lb/y) of copper, propelling it to world-class status among copper mines. The total investment was more than $1.9 billion. The Morenci mine is a joint venture (85:15) with Sumitomo Corp. The expansion project represented an incremental increase in capacity of 225 million lb/y of copper over the course of the mine’s 30-year life. The centerpiece of the expansion is the refurbished Metcalf mill, which has been shuttered since the late 1990s.
To say Freeport is bullish on copper would be an understatement. They also view exploration as an investment rather than a cost. “When Freeport acquired Morenci, we drilled the heck out of it,” Conger said. Explaining the company’s attitude toward exploration, Conger cited Freeport’s Chairman Jim Bob Moffatt, who said exploration drives the mine plan. Geologists had been waiting for this opportunity to demonstrate that large undiscovered resources of millable ore existed beneath the proven reserve. Their beliefs were soon confirmed.
Three years into a 7-year exploration drilling program, Freeport knew they had discovered a huge resource and they wanted to bring those copper volumes forward as quickly as possible. “We have been very successful with the exploration drilling program at Morenci,” Conger said. “We added 8 billion lb of recoverable copper to the reserve. That was really the beginning of this huge opportunity.”
The newly discovered sulphide reserves would require additional mining and milling capacity. Ordinarily an expansion of this magnitude would require new permits, but Morenci had the permitted capacity in place. “The property is permitted to treat 125,000 tons per day (t/d) and at the time we were considering the expansion, we were treating 55,000 t/d,” Conger said. “To add back, 70,000 t/d, seemed like a straight forward proposition, especially considering how much of the infrastructure was still in place.”
When copper prices bottomed out in the late 1990s, Morenci looked at its reserves, the economics and decided to idle milling operations in favor of heap-leaching techniques. “In the early 2000s, we started crushing and stacking leachable ore on the pads, which sustained the mining operations,” said Josh Olmsted, senior vice president, Morenci operations. “During this period, most of the exploration efforts focused on identifying leachable mineralogy.” The existence of the oxide cap indicated a large sulphide deposit below, but the Morenci miners never had the budget to properly drill the reserve.
When copper prices rebounded, Freeport began to re-evaluate all of its copper mining properties as far as what made the most economical sense. Morenci was definitely on the short list, explained Rick Coleman, president, Freeport-McMoRan Mining Co. “During the 2006-2008 boom times, the Morenci concentrator—the 1941 version—was brought back online,” Coleman said. “Then we experienced the 2009 downturn in prices. We considered mothballing it. While reviewing all of the copper operations, Morenci quickly surfaced as the leading prospect in terms of being able to deliver copper to the market quickly. Certainly as far as permitting, it was the fastest mine we could permit.” Milling would become the future growth option for Morenci.
Fast-tracking the Metcalf Mill Upgrade
As the company moved forward with the Morenci expansion plan, the engineers envisioned the Metcalf concentrator as an energy-efficient concentrator, which is the highlight of this facility, with the ability to ramp up quickly to full capacity. “From day one, we were designing a completely energy efficient process with large equipment and high throughput—large ball mills, a large hydraulic roll crusher (HRC), etc.,” Coleman said. “We also considered other equipment, such as vertical mills instead of ball mills, but we selected systems that achieved our objectives and presented the least amount of risk for a condensed timeline.” The idled Metcalf Mill (named for Jim and Bob Metcalf, the U.S. Cavalrymen who made the original discovery) would be updated with new convention balls mills and an HRC, which was the largest unit ever built at the time.
The Morenci mine and mill expansion was a fast-track project. “It was started before all of the engineering could be completed,” Coleman said. “Because of this, we decided it was prudent not to take on many risks. Bringing the concentrator online this fast would require innovative thinking and a lot of extra effort.” Gathering the best talent, the company started pooling its resources; they assembled a great project management team.
Construction commenced in 2012 and the mill was commissioned within budget in 2014. “The plant reached commercial production at 6:30 p.m. on May 21, 2014, with the first concentrate coming off the column flotation cells,” Olmsted said. “That was first froth over the lip.” Today construction is substantially finished. Morenci will complete a molybdenum circuit, which will produce 9 million lb/y of moly, and an expanded tailings storage facility (TSF) during 2015.
Knowing full well the upside potential at Morenci, the mill was designed to run either in a purely energy-efficient mode or, if the company wanted to dial it up, it could. “While we originally targeted 55,000 t/d for that circuit,” Coleman said. “We purposely sized the ball mills to process more than that. That’s something other companies wouldn’t do because we were committing more capital than what was needed, which would be a determining factor for project investment.”
Freeport didn’t have to add a lot to the circuit to get it to run at its current 70,000-t/d design rate. They increased the installed horsepower on the variable speed cyclone feed pumps together with some of the flotation circuit pumps. They also had to upgrade some pumps. The front end (the HRC) and the back end (the flotation cells) were sized properly.
The plant is running well. “The record so far is 88,000 t/d,” Coleman said. “We are still working through some debottlenecking issues. It will run above design rate.” Overall plant commissioning went relatively well. Startup tracked along the lines established by the McNulty Series 1 ramp up curve.
It wasn’t entirely smooth sailing. Some of the contractors were unable to keep up with project’s pace. Freeport also encountered a few issues with the HRC, which was built in conjunction with Metso. “This was model No. 1 and you would expect a few issues,” Olmsted said. “The gearboxes had vibration issues with which the internal components could not withstand. This was a technical issue that we were able to solve.” Working with Siemens and Flender, Freeport redesigned the gearboxes which caused some downtime. One of the new gearboxes has been installed and it is performing well. The second gearbox will be retrofitted during a planned shutdown.
“We went into this with eyes wide open, knowing full well that, in order to bring this project online quickly, we would have to move forward with less of the engineering completed than we normally would,” Olmsted said. “The company as a whole, from engineering to project management and the field people in Morenci, rallied and helped overcome many of the issues encountered. That allowed us to move faster than we would have otherwise.”
The decision to move forward on Morenci was an easy one to make, Conger explained. “The only way to take it to the bank, however, was to jump out of blocks and start building it as fast as we could,” Conger said. Citing an expansion at Cerro Verde in Peru, Conger said the lengthy permitting timeline was the reason they had 80% of the engineering completed before they started construction.
Crushing and Grinding Flexibility
The building shell of the Metcalf mill was reused, which saved on some construction costs. “Using the structure was is big opportunity to reduce capital costs,” Coleman said. “It’s a large structure. Steel and steel construction costs are high. We took the inside of the building apart. We added an HRC building and ball milling building.”
The upgraded mill has the latest in process control systems, which are fully automated. “The flotation circuit—rougher, cleaner, and regrind—is housed inside the old plant,” Coleman said. “We also reconditioned two of the old tailings thickeners, reconfiguring them and adding more power.”
The ball mills are geared as variable speed, which means they can run in full production or in an energy-efficient mode. “The energy-efficient mode would be lower ball charges and slower speeds,” Coleman said. “We’re happy to run at full load and make as much copper as we can at the upgraded design rate of 70,000 t/d.”
This is physically the largest HRC ever built, Coleman explained. “With 11 MW of installed power, it has processed more than 120,000 t/d in a closed-loop configuration, where the crushed material passes through a screening circuit and the oversized material returns to the HRC,” Coleman said. The Morenci HRC has 3- x 2-m rolls. Previous versions are 2.6 to 2.8 m in diameter and 1.6 to 1.8 m wide.
The Morenci HRC is flanged and that’s what really differentiates the machine from other roll crushers. “Other roll crushers would typically experience a 15% bypass,” Coleman said. “This unit has one tire with flanges on both sides that forces all of the material to pass and see the crushing surfaces.”
Freeport worked with Metso under an exclusive arrangement to develop the technology. “There was a high level of collaboration between Metso, the Morenci mill and the engineers in Freeport’s corporate headquarters in Phoenix,” Coleman said. “We have proven the technology.” Metso can now sell this equipment to other mining companies.
The expansion project also included Morenci Canyon, which holds the secondary crushing and screening portion of the project. Material coming from the mines is crushed (primary), screened and crushed (secondary) before being transported via a long series of conveyors to the Metcalf mill. The project also entailed upgrading a tailings thickener, concentrate thickeners and a tailings pumping facility. The new molybdenum plant was commissioned in January. And, an expanded TSF will be in full operation by September.
Revitalizing the Community of Morenci
Morenci is a resilient company town and it’s a reflection of the swings in copper markets over the last century. After the latest copper market downturn, Morenci mine production was reduced to 500,000 t/d and the community suffered. To support the expansion and the increased milling rate, the mine would have to increase production to 900,000 t/d. The vast majority of the additional workforce needed to support the Morenci expansion would be in the pit as far as additional truck drivers and support equipment operators.
As construction advanced on the mill, the search for human resource began. “We had to incrementally add 400 to 450 people to the Morenci mine’s workforce,” Olmsted said. “At the same time, we also recognized the need to improve the town site.”
Morenci is a rugged, remote outpost. Attracting, hiring and retaining people would be key to the project’s success. The community where the miners reside is an integral part of the decision for families. They needed to improve the quality of life for the people of Morenci.
The town had not seen a significant investment in more than 20 years. Freeport added 300 housing units (200 apartments and 100 homes). They improved the roads, built parks and constructed a new school, which they donated to the local school district. “We built a new daycare facility and a new state-of-the-art community recreation center,” Olmsted said. “Morenci has become more of what most people would expect from a community. The changes have improved the quality of life and it also acts as a recruiting tool.”
The additional miners that Freeport recruited were a mix of experienced and inexperienced hands. In a sense, they robbed Peter to pay Paul. The other Arizona operations—Bagdad, Chino, Sierrita and Tyrone—ponied up people. Freeport reached out to the Apache Nation and established the San Carlos Training Institute on the reservation to educate potential employees. “It has been a tremendous opportunity for the people on the reservation, which has 85% unemployment,” Olmsted said.
“The improvements to the community of Morenci have been a real boost for Freeport,” Conger said. “Sure, the mill expansion is important. But, making that investment in the town site works wonders for morale and keeps the people engaged—it’s all additive. We had challenges with this project every day. When people are motivated to overcome those challenges and make things work, it becomes fun.” A new chapter begins for Morenci, which continues to reinvent itself and improve with time.
Winning as a Team
The decision to expand was embraced by the people of Morenci. “We have a great safety culture throughout Freeport and that is prevalent at Morenci as well,” Conger said. “The two cornerstones at Freeport-McMoRan are fatality prevention and personal accountability. Working with those two priorities in mind, we completed this expansion with no fatalities and a very commendable reportable injury rate. This also helps as far as completing the project in a timely manner and within cost objectives. The most important thing is that our people return home in as good of condition as when they arrived at the gate.”
Coleman cited Freeport’s willingness to shares resources between operations and projects as one of the main reasons for the project’s success. “There has never been any hesitation to get people to assist anywhere from material management through to construction supervision,” Coleman said. “We bring resources from around the world to jump on these jobs. It builds morale and a high level of self-satisfaction—we’re good at it.”
HRCs and high efficiency, variable speed ball mills will set the stage for the way Freeport does business moving forward. “Roll crushing is very advantageous to us,” Conger said. “The improved results we are getting in flotation are the direct result of that crushing circuit. It’s in the neighborhood of 40% to 50% more energy efficient than a SAG circuit.”
Demand for copper will continue to grow and the technology Freeport has developed will likely change the way the copper business operates as whole. This especially holds true for the Chilean copper mines contemplating expansion in a high-cost power market.