Copper World’s high production of sulfuric acid poses serious pollution and water depletion threat to Santa Cruz River Valley

Hudbay Minerals’ radically revised plan to mine copper from the Santa Rita Mountains 35 miles south of Tucson increases water use and threatens to further contaminate the Santa Cruz River basin by relying on a rarely used copper ore processing technology that will generate millions of tons of sulfuric acid, according to information released by the company and previous environmental studies.

Toronto-based Hudbay published a Preliminary Economic Assessment (PEA) for the Copper World Mining Complex in a June 8 press release. The PEA provides a general description of a $2.8 billion mining plan that straddles both sides of the Santa Rita Mountain range.

Hudbay’s previous plan to construct the Rosemont mine on the east side of the range was projected to cost $1.9 billion. The company said it would release a technical report providing more details as an addendum to the PEA within 45 days.

According to the PEA, Hudbay intends to blast three, relatively shallow, open-pit mines on the west flank of the Santa Ritas in the initial years of a 44-year project – more than twice as long as the former plan to develop only the Rosemont mine. Hudbay says it will begin processing copper ore from the much larger Rosemont pit, now called the East pit, starting in the third year.

Sulfide ore from primarily the East/Rosemont pit will be used partly to generate millions of tons of sulfuric acid on-site. The acid will be applied to crushed copper oxide ore found primarily on the mountain’s west side to extract a copper-laden solution. Millions of tons of unused sulfuric acid will be offered for sale.

The PEA states the East/Rosemont pit will provide about 75 percent of the ore in the Copper World complex over the project’s life, with 340 million tons of ore from the three west-side pits and 1 billion tons from the East/Rosemont pit. In the first 16 years, mining will be nearly equally divided, with 216 million tons of ore coming from the west pits and 224 million tons from East/Rosemont.

Hudbay says all work in the first 16 years will be on private land and patented claims on federal land that total approximately 4,500 acres. Last year, the company submitted a Rosemont Copper World Reclamation Plan to the Arizona State Mine Inspector that indicated Hudbay intends to construct copper processing facilities on the west side of the range southeast of Sahuarita.  Hudbay told the Green Valley News that the Santa Rita Road will be the main access to the site.

Despite being years away from deciding whether to develop Copper World, Hudbay has already begun bulldozing land on the mountain’s western flank in preparation for waste dumps. The company states it will release a preliminary feasibility study by the end of 2022 and a final one by the end of 2023. Canadian securities regulators require the reports. Hudbay expects to decide on developing Copper World in early 2024.

Mine plan modifications will increase water demand

Hudbay has made at least six significant changes to its previous mining plan that focused only on excavating the mile-wide, half-mile deep East/Rosemont pit that will increase water demand.

Hudbay has claimed since purchasing Vancouver, B.C.-based Augusta Resource Corporation and acquiring the Copper World and Rosemont sites in 2014 that Rosemont alone would use up to 6,000 acre-feet of water a year – an acre-foot is equal to approximately 326,000 gallons.

Hudbay has provided no estimate of how much water the greatly expanded Copper World project will use. Hudbay intends to pump groundwater from deep wells it owns near the Santa Cruz River and transport it through a pipeline up to the Copper World mine site. State law allows mining companies to pump unlimited groundwater for mining operations.

“The amount of water required for operations will be determined by the size and technology of the final project as permitted,” Hudbay stated in response to questions from the Green Valley News.

The PEA identifies six new processing facilities at Copper World, all of which will consume water. These include:

• Construction of three water-intensive, conventional tailings impoundments on the mountain’s west side spread over 756 acres will cost $20 million. The water-laden tailings are a byproduct of copper ore processing operations. The tailings will be moved through pipelines to the impoundment areas.

• Construction of a $45 million oxide ore heap leach facility where crushed oxide ore will be soaked with a mix of sulfuric acid and water to extract copper into a solution that will be further processed on-site. Hudbay plans to process approximately 200 million tons of oxide ore over the life of the mine. In 2012, Augusta Resource abandoned sulfuric acid leaching for oxide ores at Rosemont for logistical reasons and environmental concerns, including reducing water consumption and eliminating potential pollution problems.

• Construction of a $250 million solvent extraction/electrowinning facility (SX/EW) that relies heavily on water to produce nearly pure copper cathode plates.

• Construction of a $77 million acid plant that will produce sulfuric acid from an estimated 973 million tons of copper sulfide ore mined over the project’s life. The PEA states that the acid plant will produce 7.3 million tons of excess sulfuric acid over the life of the mine. Hudbay projects it will sell the sulfuric acid for an average of $145/ton.

• Construction of an $88 million sulfide concentrate leach plant that will extract a copper laden-solution from sulfide ore. Hudbay says the sulfide concentrate solution will be mixed with leachate from oxide ore and processed in the SX/EW plant to create copper plates, thereby eliminating the need for smelting. The copper industry rarely uses this method to process sulfide ore concentrate. (See below)

Not only is Hudbay adding water-intensive facilities, but the company has also eliminated a long-touted plan to use “dry-stack” tailings where most of the water is extracted from the tailings slurry and reused on site. Hudbay says it expects to eventually construct a dry-stack tailings impoundment in the future if it can obtain federal permits to dump waste rock and tailings on about 2,500 acres of Coronado National Forest on the eastern side of the range.

That plan, however, has been blocked by federal court decisions. A 2019 Tucson federal court ruling, that was upheld in May by the 9th Circuit Court of Appeals, determined the Forest Service violated federal law when it approved Hudbay’s plan to use the public land for mining waste.

Nevertheless, Hudbay states in the PEA that it intends to use the same Forest Service land in the future for dry-stack tailings and waste rock without explaining how it addresses the court rulings.

Copper World facilities increase the risk of water pollution

The addition of the three conventional tailings impoundments, as well as the oxide ore leach pads and extensive use of pipelines to move tailings from processing operations to waste dumps, have a long, well-documented history of polluting surface and groundwater at other U.S. copper mines.

Two reports (2012 and 2019) prepared by Earthworks, a Washington, D.C.-based environmental group that monitors U.S. mining operations, determined that about 90 percent of the nation’s large-scale copper mines have failed to control mine wastewater, “resulting in significant water quality impacts.”

“Our research shows that water quality impacts to surface and/or groundwater are common at currently operating copper porphyry mines in the U.S., resulting from three failure modes (pipeline spills or other accidental releases, failure to capture and treat mine seepage, and tailings spills or impoundment failures),” Earthworks researcher Bonnie Gestring wrote in the 2012 report.

“These failures resulted in various environmental impacts, such as contamination of drinking water aquifers, contamination and loss of fish and wildlife and their habitat, and risks to public health. In some cases, water quality impacts are so severe that acid mine drainage will generate water pollution in perpetuity,” she added.

The two Earthworks reports highlighted the Sierrita Mine located about 10 miles west of Copper World. Sierrita has been plagued by repeated failures of pollution control systems and pipeline breaks that have resulted in widespread groundwater contamination beneath the unincorporated retirement community of Green Valley 30 miles south of Tucson.

“Seepage from the 3,600-acre tailings pond at the Sierrita mine has sent a plume of contaminated groundwater toward Green Valley…causing drinking water wells to record high levels of sulfates,” the Earthworks 2019 reports states.

“The collection system failed to capture the contaminated mine seepage completely. Public water supply wells owned and operated by the Community Water Company and serving the community of Green Valley has been affected by the sulfate contamination,” the report states.

Sierrita’s owner, Freeport-McMoRan, a Phoenix-based multinational mining company, entered into a mitigation agreement with the Arizona Department of Environmental Quality in 2015 to pump the sulfate-contaminated groundwater to reduce the plume’s impact on drinking water supplies. Sierrita has copper reserves that could sustain mining operations until 2089, Freeport-McMoRan states.

Neither Hudbay’s mining reclamation plan nor the PEA provides details on how the three conventional tailings impoundments and the oxide heap leach pad will be constructed. The PEA also provides no details on what water and air pollution controls will be included at Copper World.

Augusta Resource identified several potential environmental problems and water use concerns with oxide heap leaching and SX/EW processing when they were eliminated from its Rosemont mining plan. These include:

• Potential discharge of pollutants into the groundwater.

• Possible discharges from the heap leach pads and process solution ponds could impact down gradient water supplies.

• Quantity of water used for mineral processing.

• Impacts to birds and wildlife that might be attracted to the solution ponds.

• Outdoor lighting needed to operate the leach pads and SX/EW facility.

• Transportation of sulfuric acid offsite.

• Eliminating heap leach and SX/EW simplifies closure and reclamation requirements.

Hudbay states that since all mining and processing operations will be on private land for the first 16 years, it only needs two-state environmental permits: An Air Quality Permit and an Aquifer Protection Permit.

The company said it will submit state environmental permit applications later this year and expects them to be approved in 2023.

Hudbay abandons conventional sulfide ore processing

Last August, Hudbay stated in its Rosemont Copper World Reclamation Plan that it intended to construct a conventional sulfide copper concentrator to produce copper concentrate that would be sent to foreign smelters for additional processing.

But that plan has been abandoned.

Now, the company’s PEA states it will add an undisclosed process to create a solution from sulfide ore concentrate that can be used in the SX/EW plant to manufacture 99% pure copper plates.

Sulfide ores, however, are typically not compatible with the SX/EW process. Most SX/EW plants around the world rely primarily on copper solutions extracted from oxide ores, which are typically found close to the surface.

In the last 20 years, mining companies have begun to develop various methods to allow some sulfide ore types to be used in SX/EW facilities to produce finished copper on site.

Two of Freeport-McMoRan’s Arizona copper mines in Morenci and Bagdad use a high-temperature pressure leaching system to convert sulfide ores into a solution that can be used in SX/EW facilities, according to Phoenix-based Metallurgium’s website. Metallurgium’s principal, John Marsden, is a former Freeport-McMoRan president from 2007 to 2009.

British Columbia-based Teck Resources Limited is also developing a copper pressure leaching technology that can be used with copper sulfide ores known as the CESL Process.

Hudbay appears to have no previous experience using sulfide copper ore in SX/EW processing. Hudbay does not use the process at its open-pit Constancia copper mine in Peru, where sulfide ore is converted into copper concentrate and exported for smelting. Hudbay has frequently pointed to Constancia as the model it would follow under its previous mining plan that just incorporated the Rosemont pit.

While hydrometallurgical technology, including the high-temperature pressure leaching systems for sulfide ore such as those used by Freeport-McMoRan, is promising, it is not without challenges.

“The transition to hydrometallurgical processing of copper concentrates will take a bit of effort as leaching of copper sulfides is difficult,” according to a 2018 abstract published on Onemine.org.