The project is located within a geological region known as the Basin and Range province, near the boundary with another geological region known as the Arizona Transition Zone.

Structural Geology
The Resolution ore deposit, lying about 4,500 to 7,000 feet below Oak Flat, is located in a structural feature called the “Resolution Graben.” A graben is an area that is bounded on the sides by normal faults and is downthrust below those faults. The Resolution Graben is bounded by the West Boundary, North Boundary, South Boundary, Conley Springs, and Rancho Rio Faults.

Resolution ore deposit
The Resolution ore deposit is approximately 64 million years old and is a porphyry copper-molybdenum deposit. It lies approximately 4,500 to 7,000 feet below Oak Flat. As defined by the 1 percent copper shell, the deposit extends over an area of at least 1.2 miles in an east-northeast direction, and 0.9 mile in a north-northwest direction

Rock types with diabase, limestone, and local breccia host and control the strongest copper mineralization. Quartz-rich sedimentary rocks and Cretaceous-Tertiary intrusive rocks demonstrate the strongest molybdenum mineralization. The highest copper grades (greater than 3 percent) are located in the upper central portion of the deposit associated with a large hydrothermal breccia body and hosted primarily in breccia and diabase. The total mineral resource at the Resolution ore deposit is currently estimated (indicated and inferred) to be 1,970 million tons (1,787 million metric tonnes), with an average grade of 1.54 percent copper and 0.035 percent molybdenum (Rio Tinto 2018).

The location and geometry of the mineralization are structurally controlled by several generations of faulting that occurred before, during, and after mineralization. Chalcopyrite is the dominant copper mineral in the deposit, with lesser chalcocite and bornite. Molybdenum occurs primarily as molybdenite. The deposit is associated with hydrothermal alteration and includes a strong pyrite “halo” in the upper areas of the deposit, containing up to 14 percent pyrite.

Resolution Copper proposes to mine the copper deposit under the Oak Flat Federal Parcel using a method known as panel caving.

Operational projections are removal of 1.4 billion tons of ore and production of 40 billion pounds of copper using a mining technique known as panel caving. Using this process, a network of shafts and tunnels is constructed below the ore body. Access to the infrastructure associated with the panel caving would be from vertical shafts in an area known as the East Plant Site, which would be developed adjacent to the Oak Flat Federal Parcel. This area would include mine shafts and a variety of surface facilities to support mining operations. This area currently contains two operating mine shafts, a mine administration building, and other mining infrastructure.

At full operation, underground mining would produce 132,000 to 165,000 tons of ore per day. Ore would be crushed underground before being transported to two production shafts that would hoist the ore to an offloading station approximately halfway to the surface. From the offloading station, a conveyor system would transport the ore underground to the concentrator complex at the West Plant Site, approximately 2.25 miles west of the East Plant Site.

Shafts and Hoist Facilities
Shafts and hoist facilities will be utilized for access to the underground workings and are integral to ore production and operations at East Plant Site.

At full production, Shafts 11 and 12 will be production shafts dedicated to hoisting ore and other rock material from the Mine. The primary crushed ore will be transported via the Lower Level Conveyor System to the production shafts and then skip-hoisted within the shafts. Although the production shafts will extend to the surface, ore will only be hoisted about 3,500 ft (1,100 m) to the skip discharge level. Each production shaft will have six high-speed skips, resulting in a total of 12 skips capable of hoisting ore. Once the skips reach the discharge level, the ore will be gravity-fed from doors in the bottom of the skip into the discharge bins. These bins will become the feeder source for the high-speed Inclined Underground to Surface Conveyor System, which will move the ore through the Conveyor/Infrastructure Tunnel to the Ore Stockpile at the WPS Concentrator Complex.

At full production, Shaft 13 will be a hoisting service shaft with lifts for delivering employees and equipment primarily to the extraction and rail haulage levels.

At full production, Shafts 9, 10, and 14 will be upcast exhaust shafts for the ventilation systems for the Mine. Shaft 9 was used in the previous Magma mining operation at the site as a production shaft, and this shaft is being deepened and rehabilitated.

Panel Caving Overview
The type of copper deposit that would be mined at the East Plant Site is a porphyry deposit located between approximately 4,500 and 7,000 feet below the Oak Flat Federal Parcel. The copper deposit that Resolution Copper proposes to mine averages 1.54 percent copper (i.e., every ton of ore would on average contain 31 pounds of copper). The proposed action would use panel cave technology, a type of block caving that is a large-scale mining method.

In general, the panel caving mining system divides the ore into large sections or panels and depends on gravity and internal geological stresses to extract ore from underneath the ore body. After accessing the area below the copper deposit through the construction of vertical shafts, a network of tunnels (vertical shafts and horizontal drifts) is excavated under the copper deposit. The tunnels would be created by standard underground techniques, including drilling, blasting, and removing the blasted rock. The network of tunnels would have four levels, each with different functions.

Once the tunnels are built below the copper deposit, the ore above is blasted to fracture it. The ore then collapses downward through funnel points known as drawbells.

From the drawbells, the collapsed ore in the extraction level would be transported through the tunnel system to a crushing facility underneath the haulage level, where the ore would be crushed by one of three gyratory crushers. Once crushed, the ore would be conveyed to a production shaft where it would be hoisted approximately halfway to the surface (approximately 3,500 feet below surface) and sent from a loadout facility to the West Plant Site via the inclined underground to surface conveyor system.

After the ore has been blasted and collapsed into the drawbells, an expansion void (or cave) within the ore body would form. Additional fracturing and ore collapsing would occur at the expansion void as a result of internal geological stresses caused by the cave, at times aided by additional blasting. The continued process of collapsing and excavating the ore would be repeated until the copper deposit is exhausted or the grade of the collapsed ore is no longer economically viable. Over the 40-year operations phase, this process would be applied at six panels adjacent to one another under the Oak Flat Federal Parcel. The mining sequence would begin away from Apache Leap in Panel 2; subsequently mined panels would be Panels 3, 1, 4, 5, and 6.

In total, about 600 pieces of mobile equipment would be used at the underground mining operations.

The run-of-mine (ROM) ore is transported from the draw points underneath the ore body by LHD loaders to haul trucks. Haul trucks transport the ROM ore underground to one of three gyratory crushers that can process a total of up to 6,889 tons of ore per hour. After a series of underground feeders, conveyors, and bins, the ore is loaded into skips that hoist the ore to an underground midway offloading station, and it is discharged onto an underground conveyor system that transports coarse (crushed) ore to the West Plant Site.

The coarse ore transported from the East Plant Site via an underground conveyor system drops onto an overland feed conveyor at West Plant Site, which transfers the ore to a covered stockpile. The stockpiled coarse ore is drawn through a series of apron feeders and a reclaim tunnel located underneath the stockpile for further processing in the concentrator building.

The overall grinding configuration at the concentrator building will consist of two semiautogenous grinding (SAG) mills, in parallel, followed by a chemical flotation circuit. Each SAG mill will be designed to operate at a maximum rate of 5,512 tons per hour. Process water will be added to the SAG mill feed to provide the correct slurry density for grinding. Chemical additives will also be added to the SAG mill feed. Several reagents will be added during different processing stages to condition the concentrate slurry. The SAG mill discharge will be screened and oversized pebbles will be conveyed to one of two pebble crushers. Crushed pebbles will be returned to the SAG mill feed conveyors. All conveyor transfer points will be enclosed in the concentrator building which will control dust emissions. The flotation circuit following the SAG mill will consist of a primary ball mill and flotation circuits followed by thickeners.

The grinding circuit will be designed to process a nominal 132,000 tons (120,000 tonnes) per day of ore based on 92 percent equipment availability for 24 hours per day, 7 days per week, and 365 days per year. The grinding circuit will be contained within a fully enclosed building and will be designed to reduce the ore from 80 percent passing 156 mm to 80 percent passing 160 microns as feed to the flotation circuit.

Resolution Copper would crush the mined ore underground and then transport it underground approximately 2.5 miles west to an area known as the West Plant Site. There, operations would process the ore to produce copper and molybdenum concentrates. The West Plant Site is the location of the old Magma Mine processing and smelter facilities in Superior. A flotation process would process the ore; no heap leach processing is proposed.

The Concentrator is expected to process a nominal 132,000 tons (120,000 tonnes) per day of ore for approximately 40 years, but it is likely that, with process improvements throughout the life of the operation, the nominal production rate will increase. The maximum throughput will be approximately 165,000 tons (150,000 tonnes) per day. However, maximum production rates may be up to 25 percent higher than the nominal rate.

Once arriving at the concentrator complex, the ore would either be processed right away or stockpiled for future proce ........