More copper produced - yet less water sucked from the aquifer, less pollution, less juice needed to power the mine and mill, and fewer trucks on the road.
Rosemont Copper now predicts that scenario for its proposed Rosemont Mine, due to recent changes in its plans to produce significantly more copper of one type and to cancel production of another.
Overall, these changes will raise total copper production 25 percent over the 21-year life of the mine in the Santa Rita Mountains southeast of Tucson, company officials say. But they say the various environmental impacts will be reduced or won't grow much, if at all, because Rosemont Copper is killing plans to use toxic sulfuric acid to leach copper oxide out of ore.
Coronado National Forest Supervisor Jim Upchurch asked Rosemont Copper in writing last month for more specifics, including how much water and energy use would be reduced, how traffic would be affected and whether the number of jobs would change.
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He also wants to know if reduced electricity use would let the company use more solar energy or make underground power transmission more feasible.
The company hasn't responded to the Forest Service or to requests for similar details from the Star.
Wary opponents, led by U.S. Rep. Raúl Grijalva of Tucson, want the Forest Service to conduct more environmental analyses of these changes beyond the nearly year-old draft Rosemont environmental impact statement. Rosemont Copper says such an analysis is not needed because the additional impacts won't be significant.
Upchurch said he can't decide that question until he gets Rosemont's response to his Aug. 10 letter. Upchurch is already under pressure from the U.S. Environmental Protection Agency to conduct a supplemental environmental review of the mine project because of a raft of other problems EPA found with the draft environmental statement. If he doesn't do more review, he has said he expects to decide on the project by December.
Richer Deposits
Rosemont's parent company, Vancouver, B.C.-based Augusta Resource, announced on July 24 that it will boost copper sulfide production, while canceling plans to use acid-based heap leaching to extract copper oxide from ore to produce virtually pure bars of copper cathodes.
Heap leaching and cathode production weren't viable - for technical reasons - due to the Forest Service's recommendation of a different mine layout than the company originally proposed, Rosemont Copper Vice President Kathy Arnold wrote to Upchurch on July 8. Also, the company is responding to public and agency concerns about potential impacts of using sulfuric acid, Arnold wrote.
But due to the drilling of 12 new holes at the Santa Rita Mountains mine site and additional analysis of other drill holes, the mine site's copper sulfide deposits are now known to be 22 percent richer than estimated in Augusta's 2009 feasibility study, the company announced. The richer sulfide ores will boost total annual production over the mine's life to 243 million pounds, compared to 194 million pounds predicted in 2009, the company said in a new feasibility study.
Opponents raised concerns that these changes would trigger more water use, generate more tailings and waste rock and require more trucks.
"This is a major departure from previous plans and represents a significant change in conditions," wrote Grijalva in an Aug. 13 letter to Agriculture Secretary Thomas Vilsack, who oversees the Forest Service. "Federal and state agencies and the public have all commented … based on Rosemont's representations.
"Rosemont has now changed those representations, which in my view makes it impossible for the U.S. Forest Service to prepare a Final EIS. This is absolutely unacceptable, contrary to commitments by the company in the original plan, and counter to the principles of fair play," he wrote. Vilsack hasn't responded.
Grijalva's fellow Democrat, Rep. Ron Barber of Tucson, said it appears Rosemont's changes are significant, so it's essential for the Forest Service to have more public review, and that reopening the environmental impact statement process may be necessary.
But Arnold wrote Upchurch that the production changes will avoid or minimize mine impacts, simplify analysis of such impacts, reduce controversy "and allow your agency to issue the final environmental impact statement … during the final quarter of 2012."
Rosemont's reasoning
Company officials spelled out their reasoning:
• Because heap leaching uses a lot of water, total water use will be reduced. But the company still wants the Forest Service to evaluate the mine's effects as if it would use its maximum legal amount of 6,000 acre-feet of water a year.
• Elimination of heap leaching will reduce lighting and light pollution and eliminate four facilities that could discharge pollutants into groundwater, and eliminate the possibility that birds could be drawn to ponds carrying toxic leaching solutions.
• The total amount of material mined will now be 1.92 million tons, less than 4 percent more than before, meaning the mine would cover the same area and the amount of material disposed won't change much. The company will be able to recover more copper from the same amount of ore.
• The 2009 feasibility study predicted the mine would generate two tons of waste rock per ton of ore; now the ratio is 1.9 to 1, Rosemont Copper CEO Rod Pace told the Star. In its news release announcing its production changes, however, Augusta said that if copper oxide mining had not been canceled, its waste rock to ore ratio would be 1.7 to 1 - suggesting an increase in waste rock production now.
• The decision to eliminate heap leaching means the copper oxide will be disposed of on the mine site as waste rock, which opponents say will make it vulnerable to leaching by rainfall into nearby washes. But Arnold wrote to the Star that "there is no leaching of this material in its natural state." Because copper oxide ores don't contain sulfide materials that react with water, you must add sulfuric acid to remove the copper oxide, said Arnold.
Don Byron, a mining engineer and Rosemont opponent living in Sonoita, disagreed with Arnold that the copper oxide waste rock won't dissolve in its natural state. He said that once this material is exposed to atmospheric conditions, it will break down and will react to water flowing into it: "The oxides will be transported off the site as well as soaking into the soil."
But otherwise, Morris Farr, board vice president for mine opposition group Save the Scenic Santa Ritas, acknowledges that the group lacks the technical ability to critique many of Rosemont Copper's other statements. That's why it wants the Forest Service to conduct a thorough review, using geologists, engineers and other scientists, he said.
On StarNet: For more environmental-related stories go to azstarnet.com/environment
Contact reporter Tony Davis at tdavis@azstarnet.com or 806-7746.
