On January 30, South32 released to the public their 215-page Mine Plan of Operations (MPO) for the $2 billion Hermosa Project. The mandated plan was submitted to the Forest Service (FS) last August and deemed complete by the FS last December. It provides a detailed concept on how South32 plans to operate the mining project from start to finish.
This extract provides some (but not all) specific proposed activities and safeguards on approximately 476 acres of FS land and does not address activities on private land. Some of the content in the plan has been redacted where deemed market sensitive, confidential or proprietary.
For additional information, here is a link to the entire plan, which includes further details about operations on private land and closure activities.
THE ROADS: The mine plans to build a new permanent and public Primary Access Road to connect the Project with SR-82 south of Patagonia about a half mile north of the Patagonia Lake entrance. Existing FS Road segments along with new disturbance of about 1.9 miles in length are planned for construction of the paved road. FS roads include about 2.6 miles of Flux Canyon Road, 2.8 miles of Barriles Tank Road, and 0.2 miles of Flux Road. The new segments include a runaway truck ramp and a bridge over Flux Canyon and Flux Roads. FS roads would be reconstructed with new culvert crossings, widening, and straightening some portions of the roads, installation of rockfall protection, grading and resurfacing which could include asphalt, soil-cement-base and/or chip sealing. Some roads intersecting the new access road may be temporarily closed during construction, but once constructed, it will be open to public use.
The new road would be about 7.5 miles long, entirely on FS land with 14-foot-wide travel lanes and five-foot shoulders on each side totaling about 68 feet in width. Guardrails and/or safety barriers are anticipated at steep embankments. Replacement or movement of existing utility poles may occur. The estimated disturbance for the road totals 100.3 acres. Twelve helicopter trips within a two-week period would be needed to move the borehole rig from one location to the next with a total of 48-60 hours needed. The road will access SR83 south of Patagonia and north of the road to access Patagonia Lake, near mile marker 13.
The new road will be used for all Project activities including large truck traffic. Harshaw Road and the Cross Creek Connector (CCC) will be used for access to SR82 (north of Patagonia) and SR90. Upon completion of the new primary access road, Hermosa will relinquish its reserved easement for the CCC and the road will become a public park amenity. Harshaw Road would remain in use throughout the life of the mine, but only for a limited number of employee trips and for emergency access.Â
New temporary roads will be constructed to access other facilities on FS land including wells, Rapid Infiltration Basins, and exploration pads described below. Estimated total disturbance for temporary roads is 38.5 acres. Some resurfacing may be required.
TAILING STORAGE FACILITY 2 (TSF2): A lined, dry-stack TSF2 is planned for construction on FS land. The current tailing facility—TSF1—is on the mine’s private land. Sulfide ore extracted from the Taylor Deposit containing zinc, lead, and silver will be crushed at the surface on the mine’s private land. Chemical flotation processing will be used at the site to separate the minerals (benefication) and the filtered tailings would be loaded into haul trucks and trucked to TSF2 on FS land then unloaded, spread with a dozer, and compacted. Waste rock may also be stored there. A complex plan to manage stormwater and weather-related degradation includes satellite imaging to detect displacement, controlled drainage channels, temporary storage at the site during monsoon events, use of quick lime to expediate moisture reduction, a lined underdrain collection pond, and rerouting seepage in the pond for water treatment. Some tailings will be used for cemented paste backfill of the underground tunnels.
DRILLING: Exploratory drilling will extend onto FS land with up to 26 surface drill pads, each pad about 150 X 150 feet to further define the orebody. At each pad, up to 10 exploration holes may be drilled in multiple directions with an average depth of 3,500 feet. Water will be sourced from the mine’s water treatment plants and about 1,000 to 14,400 gallons of water would be used per 12-hour shift, per rig. The exploratory workforce, assuming 10 drill rigs running at once, would be about 70 personnel. In addition to the 26 drill pads, about 17 additional pads would be constructed within the footprint of the future TSF2 on FS land. Exploration activities at the surface and underground for metallurgical testing of the orebody will occur throughout the Project life on both South32 and FS land.
BASINS: Two Rapid Infiltration Basins (RIB) are anticipated for construction. Each RIB will have two or more basins filled with treated water between 12 and 18 inches in depth, allowing the water to infiltrate the subsurface to return to the aquifer.
WELLS: Up to six Groundwater Management Wells (GWM) may be installed and operated on FS land. This would necessitate temporary access roads, power lines for well pumping, pipelines to convey pumped water to water management facilities and treatment. Contingency sites would be used if necessary, depending on the overall capabilities of the underground water management system. Most wells are projected at 2,000–3,000 feet. Installation of monitoring-wells to satisfy state permitting requirements may also occur on FS lands.
WATER: The four sources of water for the Project include groundwater from GWM wells, groundwater from underground workings, collected stormwater and potable water hauled to the Project by truck. The primary source of water for construction, benefication and other uses will be groundwater from underground or GWM wells. During the mining, it is expected that groundwater recovered from groundwater management will exceed operational use requirements and will be treated and discharged. Discharge will occur into Alum Gulch, Harshaw Creek, into the rapid infiltration basins, and runoff from allowable stormwater discharges into natural surface drainages.
SAFETY: Construction and maintenance of fencing and berms are required for worker and public safety and to restrict public access in certain areas during operations. On FS land, fencing will surround TSF2, the Southern Restriction Area encompassing multiple functions, and within the immediate areas surrounding wells and basins. In areas of high public presence, the mine expects to install 6-foot high chain-link/barbed-wire fencing and metal gates. Two guard houses on private land, routine security patrols and security cameras will be deployed.
BLASTING: Operations at the mine are expected to occur 24 hour per day, 365 days per year with periodic maintenance or operational suspensions. The workforce will typically operate on a three-shift basis. Typical underground blasting operations will happen on average twice per day and typical surface blasting operations during construction of the primary access road and TSF2 are estimated to occur two or three times per week.
May 13, 2024 is the target date to publish the draft Environmental Impact Statement (EIS) in the Federal Register to begin both the public comment period and concurrent EPA review to assess the mine’s environmental consequences under the Clean Air Act and the National Environmental Policy Act.
May 2025 is the target date for the final EIS to be published opening another public review period and a final decision for approval of the plan is targeted for July of 2026.