Capstone nearly doubles the original capacity of its six ball mills.

Teaching an old dog new tricks

By Steve Fiscor, Editor-in-Chief, E&MJ

Capstone Copper operates the Pinto Valley mine in Arizona’s Globe-Miami mining district. During 2020, the operation produced more than 119 million lb of copper and it was on track to beat that figure for 2021. During Q3 2021, the company reported a year-to-date production increase of 13% compared to the same period last year. It attributed the improvement to higher head grades for 2021 (0.34% versus 0.30% in 2020) and improved flotation plant recovery performance (87.3% versus 84.5% in 2020).

Pinto Valley recently completed its $31 million PV3 Optimization project, which took place in two phases. Phase 1 work was completed in 2020 and it included improved blast fragmentation processes, installation of two new secondary crushers, and nine new screen decks, as well as one new ball mill shell. As a result, Pinto Valley was able to reliably achieve throughput of 58,100 metric tons per day (mt/d) in Q1 2021.

Phase 2 of the PV3 Optimization work was completed during Q3 2021. Capital was invested into tailings thickeners, pumping upgrades and installation of a second new ball mill shell. In September, milled tonnage reached 60,212 mt/d and a new monthly record was set in October at 60,758 mt/d.

They are posting those figures from the same six mills that were installed at the mine in 1974. At the time, they were billed as the world’s largest, processing 6,047 mt/d, and today peak processing rates exceed 11,900 mt/d.

“These mills are small by SAG mill standards, but we are pushing them to run basically twice the tonnage that they were being put through when they were installed 45 years ago,” said Mike Wickersham, general manager for the Pinto Valley mine. “As far as the ball mills themselves, we have replaced mill shells on two of them. There is some worn steel in a couple of the mill shells, and we’re planning to replace two more. They are the same size as the old ones just running harder.”

Even though PV3 Optimization may be complete, Wickersham and his team are always looking at innovative ways to improve the operations. “We are using many different tools to make the whole place run a little more efficiently and effectively,” Wickersham said. “Some mining operations rely on one platform to solve all the problems. We found we could solve problems with lots of different solutions.” He discussed how the mine is using new equipment and technology to improve safety, modelling, reliability, productivity and efficiency.

A dozer operator works from an office setting.

Improving Safety

In 2020, Pinto Valley began testing cameras from EDGE3 Technologies, which identify fatigue and other at-risk behaviors. “We have had some serious fatigue incidents,” Wickersham said. “Nobody has been hurt fortunately, but we knew we had a problem. Onboard facial recognition cameras turned out to be a pretty good solution for us, and it’s really reduced the number of chronic fatigue incidents. We still have some issues where people get sleepy. We can now detect it before it becomes a problem.” Today, the mine’s fleet of 23 haul trucks are all equipped with the technology.

Capstone also uses two slope-stability radar systems supplied by IDS Georadar and Ground Probe featuring rear aperture radar that gives precise, targeted monitoring for key areas throughout the pit. Pinto Valley also monitors 40 prisms with a laser monitoring system that links with Cloud-based Sensemetric for recording and reporting data. “We operate a large mine with a deep pit and, like most mines, we rely on this technology to monitor slope stability,” Wickersham said. “This is a data acquisition platform that allows us to collect remote data from different aspects of the operation. So, whether it’s tailings impoundments or reservoirs, pump or slope stability, all that data could be gathered and monitored.”

To protect its workers from hazards working around the stockpiles, Pinto Valley has been using teleremote technology on dozers. “We had a couple of instances with material sloughing on stockpiles and we were worried about a possible rollover,” Wickersham said. “The draw points beneath the piles create void spaces and we had a couple of close calls. We were concerned, so we just removed the operator from the cab entirely.” The operators now run two dozers from an office environment.

In the mill, technicians use a concave liner handling system to improve safety while maintaining crushers. “This system doesn’t have any bells or whistles or sophisticated electronics,” Wickersham said. “It’s a mechanical tray that holds all the concave liner segments. So instead of flying multiple pieces in and out over time, you just load it all up, and transport one big load. It’s a safer and faster process and we have fewer instances where people are at risk with overhead loads going back and forth.” Liner changes consisted of 50-plus crane picks and lasted approximately 57 hours. When the setting rings were used, the crane picks were reduced to five and the job was completed in about 46 hours.

Capstone uses aeronautical drones to survey dumps, leach pads and tailings storage facilities (TSFs). “We use those to look at the pit for confirmation of our dig plans on each bench,” Wickersham said. “We use it for surface contours for our deposition of tailings. It’s just a very handy tool that we use weekly.” The data is used in conjunction with Propeller to produce a 3D map used in planning and volumetric surveys.

Drone bathymetry survey equipment (small, unmanned watercraft) is used to measure the bottom of the ponds to produce a plot file of coordinates to easily understand the current situation for planning purposes. “Water is a such a precious commodity in Arizona and we have to carefully monitor it,” Wickersham said. “We needed more than a surface survey drone, so we do bathymetry and that unmanned boat lets us get the actual volume of water with depth.”

Modelling and Digital Twins

Even though it’s a smaller operation, Pinto Valley is an avid user of digital twins. “Our water twinning is done with GoldSim and we use Qerent for our production digital twin, which lets us model costs and tons across the entire value chain,” Wickersham said. “We have the standard tools that any modern mine would have for modelling geology, the orebody, the pit, ore grades, etc. The digital twins let you run the business with the proper models.”

Implementing the GoldSim water model has allowed Pinto Valley to effectively model water usage and conservation, while providing a platform to make sound production decisions relating to water usage.

Partnering with BSC Corp., Capstone constructed a digital twin for the Pinto Valley operations using Qerent, which allows them to create any scenario and compare it to what was budgeted and planned throughout the value chain. Ultimately, Wickersham said, the digital twin allows more informed business decisions. Pinto Valley also uses several different software suites to model lithology, grade and blastability.

A mechanical concave tray improves safety during crusher maintenance.

Monitoring for Improved Reliability

To improve reliability, Pinto Valley turned to AspenTech analytics, motion amplification cameras (MACs), SPLIT cameras and Sensoteq sensors. “We talked with Google and IBM about big data and data analytics solutions,” Wickersham said. “You can collect lots of variables from the plant with these big data analytics systems. They can give you correlations, but it’s a mathematical oddity when you discover them and the real question is: What do I do about it?”

Ultimately, Capstone decided to use AspenTech and they installed field devices and deployed software to provide early warning of potential failures, which could lead to extended downtime on critical equipment. “AspenTech defines steady-state operating systems with multiple variables, being measured from crushers, ball mills, etc.,” Wickersham said. “They then look for departures from the steady state using agents, like those in The Matrix. They look for insipient departures. Instead of sending out an alarm, like a traditional distributed control system (DCS) that simply reports a high sump level or high bearing temperature, it says you’ve got a 30% chance of failure in this system based on bearing temperature in two weeks, or you have a 40% chance of catastrophic failure in four days based on particulate count in a lubrication system. It’s a more sophisticated way to define a departure from the norm, rather than just having an alarm.” He said lost production revenue from catastrophic failure more than outweighs the cost of this investment.

Using MACs demonstrated to Pinto Valley that a loose nut had allowed the crusher’s mainframe and its grouting to separate. This could be seen through an excessive amount of flexing in the crusher’s mainframe and countershaft. With this early assessment, the maintenance department could schedule a foundation repair without interrupting production.

“Basically, you take a digital video of a piece of operating equipment and the system looks at every pixel mathematically for slight variations or color changes and interprets that as a change in movement, then it amplifies that as a color change,” Wickersham explained. “Visually imperceptible vibrations that you might be able to feel with your hand or hear with your ears are translated to video in motion, jumping up and down, and that turns into detecting broken bolts or cracked frames or inadequate grouting in pedestals. It’s a really, really helpful piece of technology.”

Capstone uses SPLIT cameras to measure fragmentation or classify distribution at the mining face. “Getting the best fragmentation is really a lynch pin in our mine-to-mill program,” Wickersham said. “We’re doing a better job of blasting and fragmentation. To know where you stand, you must measure fragmentation and these SPLIT cameras let you do it.”

When he talked about the Sensoteq sensors, Wickersham explained that it is an expansion of the mine’s digital footprint for the physical assets. “For a plant that was built in 1974, having more instrumentation was really necessary for us to monitor the assets in a more effective way,” Wickersham said. “These little Bluetooth sensors that can be loaded on to just about any piece of machinery provide real-time condition monitoring.” Capstone plans to mount nearly 150 Sensoteq wireless sensing devices on key equipment.

Capstone upgrades two thickeners to handle up to 70,000-mt/d total plant output.

Productivity and Efficiency

Capstone recently began running Cat’s MineStar Fleet Management System using equipment assignment optimization. “For our fleet of haul trucks, we’re using the same system to manage productivity and dispatching from load point to dump point for the entire mining cycle,” Wickersham said. “This improves efficiencies of queue times at the source.”

Pinto Valley uses onboard drill data acquisition to calculate the blastability of the rock. “If we’re able to get some intelligence about how hard or how competent the ore or the waste is, we can modify our blast design and get much, much better blast fragmentation,” Wickersham said. “The fragmentation program using the SPLIT cameras really starts with the onboard data acquisition on the drills.”

The mill is using an advanced process control (APC) system that overlies a classic DCS. “Instead of a supervisor in the control room trying to run six ball mills manually, the APC runs it for optimization and the mill operator supervises the supervisory program. It just makes it much easier to optimize six mills running in real time, rather than trying to do it manually.”

As far as material handling, Pinto Valley has had a great deal of success with the Cat 994K wheel loader. It is equipped with the latest EPA Tier 4 engine technology that along with a redesigned powertrain consumes 30 less gallons of fuel per hour than the shovels. “The 994K loader is more flexible and just as productive as the large track-mounted excavator it replaced and saves 410,000 gallons of fuel and millions of dollars in maintenance,” Wickersham said. “We have two of them now and we are considering the purchase of a third in 2022 or 2023.”

Capstone has been replacing the original secondary crushers with Raptor cone crushers, which increase throughput from 1,200 mt/h to 1,500 mt/h. “Moving from the crushers that have been in place for 45 years to these modern higher-capacity crushers is a big step forward and just lets us fill the fine ore bins so the mills can run a high capacity all the time,” Wickersham said. “We have got nine total crushers, three secondaries and six tertiaries, and we’ve upgraded two of the secondaries. If we need to go through another round of debottlenecking, we will probably take that third one as well.”

With all of the improved fragmentation in the mine, the screens were about to create a bottleneck. Capstone installed new screen decks and reduced the recirculating load allowing for an increase in the capacity reporting to the fine ore bins. “We needed more surface area because we have many more fines coming through than before,” Wickersham said. “We needed to be able to screen it away and send it to the mills without bogging that system down. We added about 20% more surface area to all those screens. That increased the ore delivery to the fine ore bins ahead of the mill, so that we can make sure we’re always keeping the mills fully fed.”

Capstone tried a new reagent it hoped would alleviate a sodium hydrosulphide hazard in the molybdenum plant. “It didn’t pan out, but in the process of mechanically refurbishing the plant, we basically doubled the amount of moly recovery,” he said.”

As far as tailings, two thickeners were upgraded to handle up to 70,000-mt/d total plant output. The upgrades included auto-diluting feedwells that enable tailings underflow densities up to 62%. “This one is a really powerful project for us. We have some instances where we lost production when the rakes in the thickener got stuck,” Wickersham said. “These are 280-ft diameter thickeners that don’t have a lift mechanism on the rakes. If you get too much mud built up, they just get jammed up and we couldn’t afford a retrofit to install a rake lift mechanism.

“With the new center well design, however, we see better settling rates, so the solids thicken and settle faster near the center, and that stops the torque from building up on the ends of the arms,” Wickersham said. “By preventing the rakes from sticking, we have much less water reporting to tailings. That’s where we have our biggest exposure to water loss, so what started as a production opportunity, turned into a water conservation project that now saves about 800 gpm of water that would have been lost to evaporation at the TSF.

Another tool being used for water conservation is interlocking HexDisks. “Some mines use floating balls, these just happened to be flat disks. In addition to this, the mine using WaterSavr, an environmentally safe application that deposits a thin layer of cetyl alcohol to slow evaporation. “It’s like throwing a stick of butter in a boiling pot of water. The oil on top prevents the steam from rising from the pot,” Wickersham explained. “Same thing in the summer with our reservoirs. You disperse a little WaterSavr and it stops evaporation by about 45%. The HexDisks slow down evaporation by about 85%, but they are much more expensive. It’s a pricey way to save water, but in Arizona with a pan evaporation rate of around 96 in. a year, it will pay off in the long haul.

“People who are unfamiliar with Pinto Valley think that we are just running an old mill and may think we are not doing much,” Wickersham said. “The reality is that we have a great copper mining and processing operation that’s using all of the latest tools at its disposal.”