The Rosemont deposit consists of copper-molybdenum-silver-gold mineralization primarily hosted in skarn, genetically, it is a style of porphyry copper deposit, although intrusive rocks are volumetrically minor within the resource area. The skarns are formed as the result of thermal and metasomatic alteration of Paleozoic carbonate and to a lesser extent Mesozoic clastic rocks. Near surface weathering has resulted in the oxidation of the sulfides in the overlying Mesozoic units however, oxidation also occurs in the underlying Paleozoic carbonates

Garnet-diopside-wollastonite skarn, which formed in impure limestone, is the most important skarn type volumetrically. Diopside-serpentine skarn which formed in dolomitic rocks is less significant. Marble was developed in the most purest carbonate rocks, while the more siliceous, silty rocks were converted to hornfels. Both marble and hornfels are relatively poor hosts to mineralization. The main skarn minerals are accompanied by quartz, potassium feldspar, amphibole, magnetite, epidote, chlorite and clay minerals. Quartz latite to quartz monzonite intrusive rocks host strong quartzsericite-pyrite alteration with minor mineralization. Where the mineralized package of Paleozoic rocks and quartz-latite intrusive outcrop on the western side of the deposit, near surface weathering and oxidation has produced disseminated and fracture-controlled copper oxide minerals. The Mesozoic and lesser Paleozoic rocks above the LAF are propylitically altered to an assemblage including epidote, chlorite, calcite, and pyrite. Copper mineralization is irregularly developed. The rocks are commonly deeply weathered and limonitic. The original chalcopyrite is typically oxidized to chrysocolla, copper wad and copper carbonates. Supergene chalcocite is locally present.

Three mineralization domains (oxide, mixed and sulfide) were defined based on the soluble to total copper ratio (ASCu/TCu) collected in the Augusta (2005 to 2012) and Hudbay (2014 and 2015) drilling programs. The oxidation and mixed mineralization occurs mainly above a low angle fault defining the contact between the Palozoic and Mesozoic rocks as chrysocolla, copper carbonates and supergene chalcocite.

Mineralization is mostly in the form of primary (hypogene) copper, molybdenum and silver bearing sulfides, found in stockwork veinlets and disseminated in the altered host rock. Some oxidized copper mineralization is also present in the upper portion of the deposit. The oxidized mineralization is primarily hosted in Mesozoic rocks, but is also found in Paleozoic rocks on the west side of the deposit and deeper along some faults. The oxidized mineralization occurs as mixed copper oxide and copper carbonate minerals. Locally, enrichment of supergene chalcocite and associated secondary mineralization are found in and beneath the oxidized mineralization.

The Rosemont deposit is a high-tonnage, skarn-hosted, porphyry-intruded, copper-molybdenum deposit located in close proximity to the surface. The Project will be a traditional open pit shovel/truck operation. It consists of open pit mining and flotation of sulfide minerals to produce commercial grade concentrates of copper and molybdenum. Payable silver and gold will report to the copper concentrate.

The proposed pit operations will be conducted from 50-foot-high benches using large-scale mine equipment, including: 10-5/8-inch-diameter rotary blast hole drills, 60 yd3 class electric mining shovels, 46 yd3 class hydraulic shovels, 25 yd3 front-end loaders, and 260-ton off-highway haul trucks.

The Rosemont final pit will measure approximately 6,000 feet east to west, 6,000 feet north to south, and will have a total depth of approximately 2,900 feet down to 3,100 feet (AMSL). There is one primary waste rock storage area (“WRSA”), which is located 1,200 feet southeast of the Rosemont final pit.

The mine phases and ultimate pit for the Project are designed for large-scale mining equipment (specifically, 60 yd3 class electric shovels and 260-ton haulage trucks) and is derived from the selected LG pit shells described in the previous section. The design process included smoothing pit walls, eliminating or rounding significant noses and notches that may affect slope stability, and providing access to working faces by developing internal ramps (including a dual ramp for the final pit). For the pit design, the targeted minimum mining width is 320 ft. and honored the wall slope design provided by Call and Nicholas, Inc. (“CNI”) and Hudbay.

Total ore reserves in the final pit are estimated to be 592 million tons. Approximately 55 million tons of medium and low grade oxide, mixed and sulfide ore will be stockpiled. This material will be reclaimed and processed during operations.

Crushing
Primary Crushing
The Primary Crusher is a 60 x 113 size Gyratory Crusher fitted with manganese steel concave and mantle liners. The primary crusher was selected based on the required mill feed rate, expected ROM feed size distribution, ore bulk density, crushing work index, stockpile capacity, and SAG feed size. The design crusher feed rate is 6,000 tons/h with a capacity of 90,000 tons/d, based on a crusher availability of 75% and a 20% catch-up capacity factor. Design parameters including the expected range of feed size distributions and crushing work indices were provided to vendors to confirm throughput performance and motor power requirements. The primary crusher dump pocket is designed to allow two trucks to dump simultaneously, one from each side. It has the capacity to hold two truckloads, approximately 520 tons in total.

A modular Crusher Control Room is located above the ROM wall to provide a direct line of sight to the dump pocket as well as the Stockpile Feed Conveyor. The Control Room includes space for crushing plant operators and two mine fleet controllers who manage the truck fleet. It is fitted with washroom and break facilities. A water spray system is fitted at each corner of the dump pocket for dust control when trucks are dumping. Dust generated in the transfer point between the Feeder and the Stockpile Feed Conveyor is captured by a dedicated Cartridge Dust Collector. Dust generated in the crusher vault is vented to the dump hopper and controlled by the water spray system.

Stockpile Feed Conveyor
Crushed ore is transferred from the Primary Crusher to the Crushed Ore Stockpile by a Stockpile Feed Conveyor. The conveyor belt is 72 inches wide and 1,014 feet in length with a 211-foot lift and has capacity to convey 6,600 tons/h of crushed feed to the stockpile (i.e. crusher capacity +10%). The conveyor is covered outside the Stockpile Dome to minimize dust emissions. The conveyor is driven by two 1,200 HP drives (one mounted on each side of the drive pulley) complete with high speed disc brake and variable speed drive for controlled start-up. The drives are located adjacent to the gravity take-up.

Coarse Ore Stockpile and Reclaim
Crushed ore for both grinding lines is stored in a single Conical Ore Stockpile. The stockpile is enclosed by a dome structure with an impervious colored fabric cover (approx. 380 feet diameter and 164 feet high).
The Stockpile Cover consists of a structural steel multi-arch frame pinned to a circular ring beam at the center of the dome and pinned at ground level to a concrete ring beam. A 20-foot-wide path around the stockpile perimeter provides access for dozer and equipment travel inside the cover. Two sets of access doors are included to allow machinery access to the stockpile area.

Live capacity of the stockpile will range between 23,000 to 51,000 tons (6 to 12 hours at full production rate and dependent on prevailing ore characteristics), representing 14% to 28% of the total stockpile capacity of 198,000 tons. Stockpile ore in dead storage can be reclaimed by heavy equipment (dozer and/or excavator) to allow for up to two additional days’ interruption of feed from the primary crusher.

Grinding
SAG and Ball Mill Grinding
The selected grinding circuit consists of two parallel SABC grinding lines, each comprising one SAG mill in closed circuit with a sizing screen and pebble crusher followed by a ball mill in closed circuit with hydrocyclones. The selected grinding mills are summarized as follows:
- SAG mills – 36 feet diameter (inside shell) x 24 feet effective grinding length (EGL) with 18 MW twin pinion drives (9 MW per pinion). Motors are controlled via an SER / hyper synchronous variable speed drive.
- Ball mills – 26 feet diameter (inside shell) x 40.5 feet effective grinding length (EGL) with 16.4 MW GMD

Mill size and power requirements were determined via Ausgrind, Ausenco’s proprietary power-based comminution calculation program using the 75th percentile values of ore parameters (ore competency and hardness). RQD was also used to adjust SAG feed size based on a correlation identified between RQD and sample depth. A +10% design factor was also added to the SAG motor specification to ensure mill power limitations would not be a significant factor for achieving throughput targets.

Pebble Crushing and Conveyor Systems
Measured ore competency shows that an SABC grinding circuit with a pebble crusher is required. Pebble crushers were selected based on crusher feed rate, ore characteristics and competency factors, pebble top size, and crusher product size. Pebble rate is expected to vary from 510 tph (15% to 25% of new SAG mill feed nominally), up to 700 tph (30% with worn SAG mill grates).

Pebbles from each SAG Mill are transferred to the Pebble Crusher Bin via the 54-inch Pebble Conveyors. Tramp metal is captured by two cross-belt self-cleaning magnets arranged in series for each crusher. The Pebble Conveyor discharges onto a diverter gate which directs the material to the Pebble Crushing Bin or allows bypass to the Pebble Conveyor Bypass Bunker or the Pebble Crusher Product Conveyor.

The Rosemont process plant includes the following unit processes and facilities:
- Primary crushing.
- Crushed ore stockpile and reclaim.
- Parallel SABC grinding lines with pebble crushing.
- Copper flotation comprising rougher flotation, concentrate regrind, and two stage cleaning.
- Cu-Mo concentrate thickening.
- Molybdenum flotation including roughing, concentrate regrind and five stages of cleaning.
- Molybdenum concentrate thickening, filtration and drying.
- Copper concentrate thickening and filtration.
- Copper concentrate load out and storage.
- Tailings thickening, filtration and dry stacking.
- Reagents storage and distribution (including lime slaking, flotation reagents, water treatment and flocculant).
- Grinding media storage and addition.
- Water services (including fresh water, fire water, gland water, cooling water and process water).
- Potable water treatment and distribution.
- Air services ( ........