Augusta Resource Corporation is backing off its announcement last summer that it was abandoning plans to mine and process 64 million tons of oxide copper ore at its planned Rosemont copper mine in the Santa Rita Mountains on the Coronado National Forest south of Tucson.
The Vancouver, B.C. speculative mining company is now stating that mining oxide ore located near the surface of the planned massive open pit copper mine remains an option.
Augusta plans to use sulfuric acid to leach a copper solution from the oxide ore dumped on to large leaching pads. An “electro-winning” facility would extract the copper from the sulfuric acid solution.
Augusta has been using its July announcement to abandon the oxide ore to place pressure on the Forest Service to quickly issue a key environmental permit by the end of the year.
Whether Augusta will mine and process the oxide ore depends on where its Rosemont Copper Company subsidiary is allowed to dump waste rock and mine tailings on more than 3,000 acres of Coronado National Forest.
Earlier this year, the Forest Service designated Barrel Canyon as its preferred alterative for the waste rock and tailings. Augusta said last July it was dropping plans to mine the oxide ore because of economic factors and other restrictions at the Barrel Alternative.
“As a result of our evaluation of operations under the Barrel Alternative, we have determined processing copper oxide ores by means of heap leaching is not viable,” Kathy Arnold, vice president of environmental and regulatory affairs for Augusta’s subsidiary, Rosemont Copper Company, stated in a July 10 letter to the Forest Service.
Two months later, in a Sept. 12, 2012 letter to the Forest Service, Augusta stated that mining oxide ore remains an option if the Forest Service selects a different location for the mine’s waste other than the Barrel Alternative when the agency releases its Final Environmental Impact Statement.
The Forest Service has been reviewing Augusta’s Draft Environmental Impact Statement since early this year. The Forest Service states on its website that a final EIS may be released by the end of 2012.
“I emphasize again that the decision to eliminate the heap leach pads and related facilities are driven largely by the economic and logistical constraints caused by the Barrel Alternative,” Arnold states in the September letter. “These same considerations are not applicable to the other alternatives evaluated in the DEIS.”
Augusta is keeping open the possibility of developing the oxide ore deposits in filings with Canadian regulators.
“Designs for leaching facilities and recovery plans for the oxide materials are being undertaken, and they may be included as ore in future studies,” Augusta stated in an August 28 feasibility study (large file warning).
Augusta gives various versions of its plans for the oxide ore throughout the 328-page feasibility report ranging from abandoning oxide ore mining, to classifying it as waste rock that will be used to build roads, foundations and retaining walls for mine tailings, to stockpiling the oxide ore for future use.
The feasibility study provided a range of options for the oxide ore reserves including:
- Page 4: “Oxide material could potentially be processed by heap leaching, to recover the copper.”
- Page 8: “No mineralized oxide materials are in ore reserves, they are included with waste materials.”
- Page 95: In addition, geologic and metallurgical studies conducted by Augusta have shown the potential for considering the oxide copper mineralization that overlies the sulfide deposit… Oxide material could potentially be processed by heap leaching, to recover the copper.”
- Page 117: “Approximately 65 million tons of mineralized oxide material, indicated to be economic, are contained in this pit and included with the waste material instead of ore for the purpose of this study. Facilities to process this mineralized material is currently assessed and a portion of it may be included as ore in the future.”
- Page 119: Mineralized oxide materials that are indicated to be economic in the optimized pit analysis are not included in the pit ore reserves for this study. All oxide materials are Designs for leaching facilities and recovery plans for the oxide materials are being undertaken, and they may be included as ore in future studies currently included with the waste materials.”
- Page 172: Augusta includes oxide ores in its analysis of truck “haul cycle times and truck productivities” on Table 16-11.
- Page 226: “Any run of mine oxide ore encountered will be treated as waste and stockpiled.”
- Page 245: “The heap leaching of oxide minerals and associated facilities, such as the heap leach pad, solvent extraction, electrowinning, and related facilities, have been eliminated.”