Summary

Deposit type

• Skarn
• Porphyry

Summary:

The Bingham Canyon deposit is a classic porphyry copper deposit containing economic values of copper, molybdenum, gold, silver, and historic lead and zinc production. Peripheral copper-gold skarns, lead-zinc fissures, and disseminated gold deposits are also associated with this copper porphyry system.

Porphyry dikes, faults, and quartz veins are steeply dipping and have two dominant orientations; north-northeast– and northwest-striking. Dikes have a north-northeast strike but they thicken and develop northwest-trending apophyses and host high-grade copper-gold zones at intersections with northwest-faults, indicating that magmatic-hydrothermal fluids were focused by these structural intersections.

Vein truncation relationships coupled with abrupt changes in copper-gold grades, sulfide ratios, and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive-hydrothermal cycles, presumably due to depletion of metals and volatiles in the underlying magma chamber.

Dimensions
The deposit is contained within a 4.5 km x 4.5 km area with a maximum thickness of 900 m and average overburden cover of 800 m.

Lower Commercial Skarn (LCS) deposit
The Lower Commercial Skarn (LCS) deposit is located in the Bingham mining district southwest of Salt Lake City, Utah. The Bingham mining district is dominated by the Bingham Canyon copper-molybdenum-gold porphyry system, which consists of the Eocene monzonite-quartz monzonite Bingham Stock and deformed siliciclastic and carbonate country rock of the Palaeozoic Bingham Mine Formation. The LCS deposit is hosted in mineralized skarn of the Lower Commercial Limestone (LCLS) unit of the Lower Bingham Mine Formation. This unit is proximal to the Bingham Canyon porphyry system and has been altered to copper-gold hosting calc-silicate skarn through prograde metasomatism with localized retrograde massive sulphide and siderite. This unit has been variably folded and faulted prior to mineralization, resulting in fold thickening and repetition of the units across faults.

The LCS deposit lies in the footwall of the southwest dipping Midas thrust fault, between the older northeast striking and steeply dipping oblique transverse Verona and Smelter faults. This structural block between the Verona and Smelter faults, and below the Midas, is referred to as the Middle Block. The Middle Block is bounded to the south by the Bingham Canyon porphyry monzonite, open to the north, and cut by late latite porphyry dikes on a northeast trend. Palaeozoic country rock within the Middle Block is folded in an asymmetric anticline, slightly overturned to the east, with a gentle plunge to the north. The LCS deposit is hosted in the gently dipping upper limb of the LCLS.

Dimensions
The LCS Mineral Resource is contained within a roughly tabular zone dipping gently north, approximately 40 to 100 m thick, extending 275 m along strike, and 450 m down dip.

The LCS Mineral Resource is located beneath the Bingham Canyon Mine open pit, at approximately the 3700 level (~1,128 m AMSL), immediately adjacent to the active underground drainage gallery workings.

North Rim Skarn (NRS) deposit
The North Rim Skarn (NRS) deposit is located in the Bingham mining district southwest of Salt Lake City, Utah. The Bingham mining district is dominated by the Bingham Canyon copper-molybdenum-gold porphyry system, which consists of the Eocene monzonite-quartz monzonite Bingham Stock and deformed siliciclastic and carbonate country rock of the Palaeozoic Bingham Mine Formation. The NRS deposit is hosted in mineralized skarn of the Lower Jordan Limestone (LJLS) unit of the Lower Bingham Mine Formation. This unit is proximal to the Bingham Canyon porphyry system and has been altered to copper-gold hosting calc-silicate skarn through prograde metasomatism with localized retrograde massive sulphide and siderite. This unit has been variably folded and faulted prior to mineralisation, resulting in fold thickening and repetition of the units across faults.

The NRS deposit lies in the footwall of the southwest dipping Midas thrust fault, west of the older northeast striking and steeply dipping oblique transverse Verona fault. The NRS is bounded to the south by the Bingham Canyon porphyry monzonite and the Midas fault, open to the north at depth. Palaeozoic country rock within the NRS is folded in an asymmetric anticline, slightly overturned to the east, with a gentle plunge to the north.

Dimensions
The NRS Mineral Resource is contained within a roughly tabular zone dipping moderately northwest, approximately 50 m to 100 m thick, extending 1000 m along strike, and 900 m down dip.

The NRS Mineral Resource is located beneath the Bingham Canyon Mine open pit, at approximately the 3200 level, immediately adjacent to the active underground drainage gallery workings.

Mining Methods

• Truck & Shovel / Loader
• Longhole open stoping
• Sub-level open stoping (SLOS)

Summary:

Kennecott is a fully integrated mining operation.

Mining operations at Kennecott are conducted using the conventional open-pit method, and since 2023, underground mining has been initiated in an area known as the Lower Commercial Skarn (LCS).

Open pit
Mining involves a sequence of drilling, blasting, loading, hauling, crushing, and conveying 24 hours a day, seven days a week, 52 weeks a year.

On average, 200 holes 55 feet deep are drilled in a typical day. Each hole is packed with 1,200 pounds of special blasting agents. Explosives are carried out twice a day.

Following the blasts, electric shovels load the ore and waste onto the haulage trucks, which transport the ore to the in-pit crusher and the non-economic material to rock repositories.

Kennecott’s fleet of haul trucks and all heavy machinery at the mine are all fueled by renewable diesel, which being used is currently a combination of 90% soybean and the remainder animal fat and used cooking oil.

Phase two of the south wall pushback to extend mine life at Kennecott by a further six years. The project largely consists of mine stripping activities and includes some additional infrastructure development, including a tailings facility expansion. The project will allow mining to continue into a new area of the orebody between 2026 and 2032.

Approved in December 2019, stripping commenced in 2020 and will continue through 2027. In March 2023, a further $0.3 billion was approved to primarily mitigate the risk of failure in an area of geotechnical instability known as Revere, necessary to both protect open pit value and enable underground development.

During the 3rd quarter of 2024, further studies on the geotechnical risks have been completed, indicating the need to change our mine plan to stabilise pit wall movement and mitigate the risk of a significant geotechnical failure, this is expected to restrict ore deliveries from the primary ore face in 2025 and 2026.

Underground mining
In September 2022, Rio Tinto approved development capital totalling $55 million to start underground mining in an area known as the Lower Commercial Skarn (LCS). Underground production within LCS started in February 2023, and first production was achieved in June 2024, marking the mine's return to underground production after more than four decades. The LCS is expected to deliver a total of around 30 thousand tonnes of additional mined copper through the period to 2027.

In June 2023, $498 million in funding was approved to deliver underground development and infrastructure for an area known as the North Rim Skarn (NRS). Production is expected to commence in mid-2025, delivering around 250,000 tonnes through to 2033, alongside open-cut operations.

These two investments will support Kennecott in building a world class underground mine which will leverage battery electric vehicle (BEV) technology.

The assumed mining method is bottom up, sub-level, long hole open stoping, using a primary secondary sequence with cemented backfill.

Stope dimensions are set at 22.9 m high, 15.2 m wide, and a variable length between 15.2 to 9.1 m. Permanent development needed to access the deposit will be 5.9 m high by 5.5 m wide, reducing to 4.9 m high by 5.5 m wide. Stope ground support has been accounted for to aid in stability and is planned for the backs and sides of the upper drift, as well as the brow from which mucking will occur.

External dilution (10% for secondaries, 2.5% for primaries) has been applied to the estimate at zero grade based on an evaluation of the geotechnical parameters with established industry empirical dilution guidelines. Given the arrangement of the mine, the majority of waste dilution is estimated to take place within secondary stopes from the adjacent backfilled primaries with a small amount within primaries from the stope in front.

Ore dilution is expected to occur within primary stopes from the adjacent secondaries with an overall net zero change in ore tonnes.

Two distinct recovery factors have been applied to the estimate, the first being a stope shape factor (92.5%) to deduct areas of the stope which cannot be practically drilled such as the stope “shoulders”. The second being a mining recovery factor (90%) to account for drilled and blasted material or dilution which cannot be mucked out from the stope.

Minimum mining widths have been established and applied to the mine design which underpins the estimate. These are based on the dimensions of the existing mechanized mining fleet, and the expected additional equipment needed to operate the mine (Including allowance for Battery Electric Vehicle (BEV) equipment size).

Infrastructure
Much of the required infrastructure for the estimate is already available via existing site facilities. This includes mechanical and electrical infrastructure operating within an established drainage gallery tunnel which is currently used to dewater the existing open pit.

Decline development will be extended from the existing drainage gallery tunnel to access the NRS and establish ventilation connections.

An additional CAF Plant will be constructed adjacent to the portal, and an upgraded underground ventilation facility will be established to achieve required airflows.

All personnel and materials will access the operation via the open pit and operations will be integrated with the existing drainage gallery maintenance.

Ore material will be rehandled at the drainage gallery portal using open pit equipment and hauled to the open pit crusher to be blended with open pit material.

The Mineral Resource estimate assumes a small footprint established in the bottom of the existing open pit, with all other major development to occur underground.

Comminution

Crushers and Mills

Summary:

At the in-pit gyratory crusher, approximately 150,000 tons of ore per day are reduced to pieces about 10 inches in diameter. The crushed ore is then transported by a five-mile conveyor system: three miles through a tunnel in the mountain and two miles above ground to the Copperton Concentrator.

Processing

• Electric furnace
• Solvent Extraction
• Autoclave
• Hydrometallurgical plant / circuit
• Sulfuric acid (reagent)
• Chloride leach
• Hydrochloric acid (reagent)
• Crush & Screen plant
• Smelting
• Flotation
• Pressure oxidation
• Electrorefining

Summary:

The operation includes Copperton concentrator, Garfield smelter, refinery, and precious metals plant and tailings storage facilities.

In-pit crushed ore is turned into a slurry and transported to the Copperton Concentrator, where copper and molybdenum concentrates are produced through a froth flotation process. The concentrate, which contains about 26 percent copper and by-products such as gold and silver, moves through a pipeline to Kennecott’s smelter, located about 17 miles to the north, for further processing.

Garfield smelter
The next stage, smelting, is a process of heating and smelting the copper concentrates to cause a chemical reaction, which removes the copper from other elements in the ore. At the smelter, large 750-pound anodes are produced and transported by rail to the refinery. At this stage, the copper is 99 percent pure.

The smelter processes copper concentrate that originates primarily from the Copperton Concentrator and periodically from other mine and mineral processing facilities, along with flux, coolants, and other reagents in order to produce anode copper, sulfuric acid, and rhenium.

The smelter at Kennecott captures 99.9 percent of the sulfur in the feed, making it one of the cleanest in the world. The smelter also recovers heat from the furnaces, which generates 60 percent of the facility’s total electricity.

Refinery
At the refining stage, the copper is in anode form. 750-pound copper anode plates are subjected to an electric current for ten days, transforming them into two 300-pound copper cathodes. This process further separates the copper from other metals, resulting in copper that is 99.99 percent pure.

Precious metals plant
The Rio Tinto Kennecott process begins with oxidative leaching in an autoclave to dissolve copper-rich anode slime (Cu > 90%), facilitating the recovery of precious metals. Following this, a filtration step separates the solutions containing dissolved metals from solid residues. Wet chlorination is then employed to dissolve precious metals and selenium.

Wet chlorination of decopperized slimes is achieved through the metered addition of hydrogen peroxide to agitated slurry of slimes suspended in an aqueous solution of hydrochloric acid. The process of wet chlorination oxidizes and solubilizes the gold and selenium in the slimes. Hydrogen peroxide is used as the oxidant and hydrochloric acid provides the chloride for gold complex solubility.

Lead is precipitated by adding sodium carbonate (Na2CO3) to form lead carbonate (PbCO3), which aids in extracting other precious metals. Ammonia leaching dissolves silver, and sodium hydroxide (NaOH) combined with sugar is used to precipitate it from the ammonia solution. The precipitated silver is melted in an electric furnace to produce high-quality silver ingots. Solvent extraction is utilized to separate remaining precious metals – gold, silver, platinum, and palladium – from the solution, followed by reductive precipitation with oxalic acid and NaOH to obtain gold in powder form, which is then melted in an electric furnace to create high-quality gold ingots. Finally, selenium is separated via reductive precipitation, while by-products containing gold, silver, platinum and palladium and refined externally to recover these precious metals.

The last step in the production process is to stamp each bar with Kennecott's brand, the lot number, the weight and the fineness of the metal — that is, the percentage of gold or silver in the bar.

Processing facilities upgrades
During 2024, Kennecott smelter and refinery returning to normal operations following the successful rebuild in 2023.

The rebuild of the smelter, the largest in Kennecott’s history, commenced in May 2023 and was successfully completed by Q4 2023.

A further $120 million was invested to upgrade the refinery tank house structure and update Kennecott’s molybdenum flotation circuit with a state-of-the art, fully automated system.

Pipelines and Water Supply

Summary:

The site holds surface water rights and shares that provide up to 80.9 GL per year of supply. Annual operational usage may be lower in a given year than the rights and shares provision, reective of the conditions experienced during the year. Where annual operational usage remains below the water rights and shares provision, bypass discharge to the Great Salt Lake is permitted as a benecial use. The long-term average runoff for the catchments associated with the surface rights and shares is estimated to be 800 GL per year.

Kennecott will reduce average annual imported water per ton of ore milled by 5% over the 2014-18 baseline of 393 gal/ton (1,487L/ton) at the Copperton Concentrator by 2023.

With the exception of 2019, annual concentrator water intensity has remained above the 2014-2018 target baseline. Required changes to the concentrator process during 2020 resulted in increased water usage compared to the initial target baseline. Kennecott’s water usage has trended down since the implementation of these changes. Kennecott’s commitment to improve water efficiency through the concentrator successfully reduced intensity in 2022 and 2023 to approximately 10% lower than the period peak recorded in 2021.

Commodity Production

Operational metrics

Personnel

Job Title	Name	Phone	Email	Profile	Ref. Date
General Manager	Chris Osborn				Mar 24, 2025
Maintenance Superintendent	Thomas Dormenval				Mar 24, 2025
Manager - Mine Productivity	Mark Smith				Mar 24, 2025
Manager Mine Operational Readiness	Braden York				Mar 24, 2025
Manager Underground Technology	Ferrin Prince				Mar 24, 2025
Managing Director	Nathan Foster	+1-406-539-2563	nate.foster@riotinto.com		Mar 24, 2025
Mine Manager	Kieran McRae				Mar 24, 2025
Mobile Equipment Maintenance Manager	Steve Woodruff				Mar 24, 2025