The Globe-Miami mining district of central Arizona includes porphyry copper-molybdenum (“Cu-Mo”) deposits associated with Paleocene Epoch granodiorite to granite porphyry stocks (65-59 million years ago). Vein deposits and possible exotic copper deposits are also found within the district.

Precambrian basement rocks throughout southern Arizona and New Mexico largely consist of early Proterozoic Pinal Schist (~1,700 million years old) intruded by granites correlative with two-mica granite batholiths (~1,450 million years old). At the Pinto Valley Mine this is represented by the Ruin granite (also referred to as the Lost Gulch quartz monzonite) that hosts the Cu-Mo mineralization. The Late Proterozoic-aged (~1,420-1,150 million years old) Apache group, comprising conglomerate, limestone, quartzite, and minor basalt units overlying the basement rocks, was intruded by 1,150 million years old Apache diabase sills of varying thicknesses. These diabase units are represented at the Pinto Valley Mine as thin dikes and sills, and commonly contain higher copper concentrations than the surrounding Ruin granite. During the Paleozoic Era, various limestone units were deposited representing the shallow, marine environment present over much of the southwestern US at the time.

Subduction of the Farallon tectonic plate (80-50 million years ago) off the west coast of the southwestern US initiated arc magmatism responsible for generating the Cu-Mo-bearing intrusions in the region. Stocks emanating from the Schultze granite, the source of the mineral-bearing fluids to the Globe-Miami mining district, were emplaced at the Pinto Valley Mine between 60-59 million years ago.

Regional Tertiary-Era Basin and Range extension and faulting following cessation of subduction facilitated the dismemberment, tilting, and exposure of the Cu-Mo deposits. They were preserved through deposition of the Whitetail conglomerate (Oligocene Epoch) and the Apache Leap tuff (Miocene Epoch). Further extension in the Pliocene Epoch deposited the Gila conglomerate into basins.

The Pinto Valley Mine deposit is bound by faults that vary in age from the Pre-Cambrian to the Tertiary. These have controlled the emplacement of the Ruin granite, stocks of the Cu-Mo-bearing Schultze Granite, and subsequent post-mineralization Basin-and-Range extensional faulting.

The primary sulphide minerals encountered at the Pinto Valley Mine are chiefly pyrite and chalcopyrite with minor amounts of molybdenite. Gold and silver are recovered as by-products when material containing sulphide minerals is processed. Sphalerite and galena occur locally in very small amounts. Alteration of silicate minerals of the host rocks to other groups of minerals due to the presence of hydrothermal fluids associated with the Cu-Mo-bearing intrusive rocks include potassic, argillic, sericitic, and propylitic alteration suites.

Sulphide minerals generally occur in veins and microfractures and less abundantly as disseminated grains, predominantly in biotite sites. The ore zone grades outward into a pyritic zone with higher total sulphide content. Molybdenum distribution generally reflects copper distribution, with higher molybdenum values usually found in the higher-grade copper zones. Oxide mineralization and a supergene enrichment blanket was developed at the Pinto Valley Mine, but these areas have since been mined.

Sulphide deposition at Pinto Valley Mine is controlled to some extent by the host rock. The sulphide content decreases in Precambrian aplite intrusions. Aplite usually contains less than 0.25% copper, whereas adjacent Quartz Monzonite may have as much as 0.6% copper. The deficiency of copper in aplite is probably due to the absence of biotite, which makes up about 7% of Quartz Monzonite. Disseminated chalcopyrite shows an affinity for biotite, where it is disseminated through the biotite or partially replacing it. Additional chalcopyrite is also present in veins cutting both rock types.

PVM is an open-pit hard-rock mine, producing copper bearing sulfide ore to a conventional milling and flotation concentrator. Conventional open-pit mining utilizes the cycle of drilling, blasting, loading, and hauling of material to the respective destinations. Ore is hauled to the primary crusher for processing and waste rock material is hauled to waste storage facilities. Mining is accomplished on 45 ft benches and the LOMP is reported in metric tonnes.

The LOMP schedules movement of an average of 144,121 tpd (52,505 ktonnes/yr) of total material from 2021 to 2031. Beginning in 2032 the waste mined begins to fall, and the total material movement reduces to slightly more than the mill ore feed rate.

PVM has been operated intermittently since the 1970s. There are areas of the existing PVM pit that have had slope stability issues over time. Specific areas are the southwest corner of the pit in the Pinal Schist and the northeast side of the pit near the Bummer Fault. Design of phase expansions in these areas must consider the geotechnical impacts and practical constraints they impose.

Areas to the east and north of the current PVM pit will be expanded. The phase that pushes back the northern wall will mine through some historic waste and leach dump material before encountering solid rock. That material is mined at a shallower angle (32 degrees) than the solid rock below.

The current PVM operation mines two phases that incorporate the current pit bottom as well as east and north expansions. PVM has also designed three pushbacks that expand the pit beyond 2027 that further develop the pit to the east and north.

In total, there are five phase designs that were used as input to the development of the PVM schedule. The mining phases are a combination of work completed by PVM staff in the long range, short range, geotechnical, and operation groups. The phase designs in order of extraction in the current schedule are: PV2C (Castle Dome), PV2B (Jewel Hill), PV3A, PV3B and PV3C.

Castle Dome phase is the current primary ore pushback on the south side of the PVM pit and will continue through 2025. Jewel Hill is an eastern pushback that was designed to continue the operation through 2027. The Jewel Hill pushback design has been continually optimized to account for geotechnical issues as well as accommodating operational challenges.

Inter-ramp slope angles for the phase design are summarized in Section 16.2. The overall and inter- ramp slopes were reviewed and recommended by slope stability consultant Edward C. Wellman of Independent Geomechanics, LLC. In addition to slope angles, the following road and pushback geometries complete the mine design parameters:
• Haul Road Width: 125 ft and 115 ft;
• Haul Road Grade: 10% maximum;
• Minimum Widths Between Pushbacks: 300 ft nominal.

Primary Crushing
ROM ore is delivered by haul truck to a Fuller Traylor™ 60 inch × 89 inch gyratory primary crusher. The trucks discharge directly into the crusher, which is set in a dump pocket. The crushed ore is withdrawn from a surge pocket under the crusher by an apron feeder, which discharges onto the primary conveyor.

The primary conveyor transports the primary crushed ore to the coarse ore stockpile, which has a nominal live capacity of 27,215 tonnes (30,000 tons). Based on digital size analysis of the primary crusher discharge, the P80 of the primary crushed ore is approximately 88.9 mm (3.5 inches). The fine product distribution is attributed to ore fragmentation and mine blasting practices. The discharge product averages 32% passing 12 mm (half inch). The quantity of fines in the feed has a significant influence on the production capacity of the FCP and this has been the focus of blast fragmentation optimization.

Secondary and Tertiary Crushing (Fine Crushing)
The primary crush ore is reclaimed from the coarse ore stockpile by six apron feeders, which feed three coarse ore reclaim belts. Each coarse ore reclaim belt discharges onto an 8 X 20 ft Ludowici double-deck vibrating screen. Two of the screen’s oversize reports to two secondary 7 ft Nordberg™ standard cone crushers and one screen feeds the new Raptor 900 standard cone crusher. Screen undersize from the secondary screens is sent to the fine ore bin (FOB), with a nominal live capacity of 40,000 tonnes (44,000 tons).

The secondary crushers operate in an open circuit. Crusher product from all three secondary crushers is forwarded via a common conveyor system to the tertiary crusher feed bin. Ore is withdrawn from the tertiary crusher feed bin by six feeders and delivered directly to six 8 X 20 ft Ludowici double-deck vibrating screens. The screen undersize from the tertiary screens is sent via a common conveyor system to the FOB. The screen oversize is crushed by six 7 ft Nordberg™ tertiary shorthead cone crushers. The product from the six shorthead crushers is added to the secondary crusher product on the common conveyor system to feed the tertiary feed bin, and tertiary crushing is operated in a closed circuit. At the current plant throughput, the P80 of the fine-crushing plant is approximately 11 mm (0.43 inches).

Grinding
Fine ore is reclaimed from the FOB and fed directly to six 18 ft × 21 ft, 2,983 kW (4,000 hp) Allis-Chalmers™ overflow ball mills. Each ball mill is an independent circuit consisting of a discharge sump, pump, and cyclone cluster. Water is added to the ball mill feed to achieve the desired percent solids content for grinding.

Additional water is required at the ball mill discharge sump to maintain the optimal operation of the cyclones. Each circuit is equipped with three 838 mm (33-inch) inclined cyclones. Cyclone overflow slurry gravity feeds the rougher flotation banks, while the underflow discharges back to the ball mill feed sump. The ball mills operate in a closed circuit with the cyclones, with a circulating load estimated at 400%.

Xanthate (SIPX), dithiophosphate (DAP), diesel, and lime are added to the grinding circuit to prepare the ore in the slurry for flotation. A pH target of 10 is utilized for flotation.

Regrind
The rougher concentrate is delivered to the regrind ball mill circuit. The regrind circuit consists of two 11 x 15-ft regrind ball mills driven by a 373 kW (500 hp) synchronous motor. The regrind circuit is a reverse configuration common for regrinding. The rougher concentrate is combined with the regrind ball mill discharge and pumped to the closed-circuit cyclones (a bank of four 500 mm (20 inches) diameter cyclones for each mill).

The cyclone overflow is fed to the cleaner flotation circuit, while the underflow is sent to two regrind mills. The regrind mills operate in a closed circuit with the cyclones. The target product for regrind cyclone overflow is P80 of 50 µm.

The PVM concentrator was built in 1973, and the basic processing flowsheet has largely been unchanged since that time. The original nameplate capacity was 36,287 tonnes per day (tpd) (40,000 short tons per day (stpd)). Significant improvements have been incorporated over the years, resulting in the current 56,000 tpd base case capacity. The PVM plant is designed to treat porphyry copper ore with minor molybdenum. The main minerals of interest are chalcopyrite and molybdenite, with by-product quantities of precious metals including gold and silver.

The PVM concentrator flowsheet includes:
• Crushing - primary through to tertiary crushing;
• Grinding – conventional ball mills;
• Flotation – copper and molybdenum - conventional cells for roughing and scavenging and columns for primary cleaning;
• Copper concentrate thickening and filtration;
• Molybdenum concentrate thickening, filtration and drying;
• Tailings thickening;
• Tailings impoundments.

Flotation
The flotation circuit operates as a bulk copper and molybdenum flotation process. Subsequent differential flotation is designed to produce the final individual copper and molybdenum concentrates. The rougher flotation circuit is operated to maximize recovery of the primary sulfide minerals from the gangue. Subsequent cleaner flotation of the bulk concentrate is operated to maximize the copper concentrate grade while minimizing copper recovery losses.

The flotation reagents used include SIBX (Xanthate), C-2420 (dithiophosphate), diesel (for molybdenum recovery) and Flottec F-171 (frother). The majority of the flotation reagents are added to the ball mill feed with “kickers” of reagents added down the flotation bank where required.

Regrinding of the rougher concentrate is required to provide increased mineral liberation to allow cleaner flotation to produce high concentrate grades. The molybdenum is co-recovered to the bulk cleaner concentrate with the copper. The molybdenum flotation circuit provides the separation of the copper and molybdenum into respective salable concentrates.

Rougher Flotation
The rougher flotation circuit consists of 65 28.3 m3 (1,000 ft3) Wemco™ cells configured into three banks each with two trains (Sections 1,2,3), with cyclone overflow from two ball mills combined to feed each of the banks. The frother is added to the head of the rougher flotation cells, with supplemental reagents added as required down the bank. The rougher section is operated in open circuit, with the rougher tailings reporting directly to the final tailings.

Cleaner Flotation
The cleaner circuit consists of four 2.4 m diameter by 12.2 m tall (8 ft diameter by 40 ft tall) column flotation cells operated in parallel. The column cell concentrate, the final copper-molybdenum bulk concentrate, contains 24% to 29% Cu and 0.35% to 0.7% Mo. The column cell tails are sent to the cleaner scavenger flotation bank. The cleaner scavenger bank comprises 15 8.5 m3 (300 ft3) Wemco™ flotation cells. The first bank of cells produces the final concentrate, and concentrate from the remaining cells is recirculated to the column cells via the regrind circuit. The tails of the cleaner scavenger bank report to final tailings.

Molybdenum Plant
The bulk copper-molybdenum concentrate from the cleaner circuit is thickened before being sent to the molybdenum plant. The plant comprises four banks of Agitair™ rougher cells of six 1.4 m3 (50 ft3) cells each and four stages of cleaning using column cells. Sodium hydrosulfide (NaHS) is added to the slurry to provide depression of copper and iron sulfides. Diesel is added as a molybdenum promoter.

Concentrate Dewatering
The molybdenum rougher tailing becomes the final copper concentrate reporting to one of two 27.4 m (90 ft) copper thickeners. The final molybdenum product is thickened in a 7.9 m (26 ft) molybdenum thickener, filtered on a disk filter, dried in a rotary dryer, and bagged for shipment. The final copper concentrate is thickened to 60% solids and flows by gravity from the copper thickeners to either of two 900 m3 (238,000 gallons) copper concentrate slurry storage tanks. The slurry is pumped from the storage tanks to the filter plant. The concentrate is filtered in an Eimco™ plate and frame pressure filter and conveyed to the copper concentrate storage shed for loadout.

Tails Thickening
Tailings from the three rougher banks and the cleaner scavenger bank are combined and feed three 106 m diameter (350 ft) tailings thickeners where overflow water is reclaimed, and the tails are thickened and sent on to the TSFs.

Process Water
Water supply for processing is delivered to the facilities through a system of above-ground and buried pipelines that generally follow road alignments. Sources include the Cottonwood Reservoir (formerly the decant pond of the now inactive Cottonwood TSF), the Mine Reservoir (a concrete-lined 2.32 acre pond) and the Peak Well system.

SX-EW
The PVM SX-EW plant was built and commissioned in 1981 to process solutions from the leach grade material placed on the run-of-mine (ROM) leach dumps north of the pit. Through 1998, approximately 450 M tonnes of 0.13% Cu material had been placed on the leach dumps, resulting in peak production of 10 to 15 M lb of cathode copper per year in the early 2000s. Over the last few years, the SX-EW has produced in the range of 3 to 5 M lb of cathode per year due to the declining residual copper inventory in the leach piles. A moderate quantity of fresh material was placed on the leach pad in 2020.

In the PV3-2016-PFS, the leach area and pregnant solution pond area were slated for future decommissioning and conversion to waste rock storage after suitable rinsing and drainage. PVM is evaluating options for continued use of select leach areas. Effluent from the dump leach will continue to be processed in the SX-EW plant for the foreseeable future.