Cactus Mine Project in the US state of Arizona is the principal asset of copper exploration and development firm Arizona Sonoran Copper Company (ASCU).
The brownfield project includes three deposits- Cactus East, Cactus West and the Parks/Salyer deposit- along with one stockpile within a 5.5km mine trend. This includes the historical Sacaton Mine, which operated from 1974 until 1984.
The company announced a positive Prefeasibility Study (PFS) for the Cactus Project in February 2024.
An NI 43-101 Preliminary Economic Assessment (PEA) on the copper project was released in August 2024. The PEA superseded the previously released PFS in all respects.
The PEA projects a life of mine (LOM) of 31 years. The development of the project is expected to cost $668m, including contingencies.
Over its operational life, Cactus Mine is expected to produce a total of 5,339 million lbs of copper cathodes via heap leaching and solvent extraction and electrowinning.
ASCU expects to complete a new PFS in the H1 of 2025 and initiate the feasibility study on the project in the second half of the same year.
Cactus Mine Location
The Cactus Mine property is located 40 road miles (mi) south-southeast of the Greater Phoenix metropolitan area and approximately 3 miles northwest of the city of Casa Grande, in Pinal County, Arizona.
The current project is located at the historic Sacaton Mine, which is 10 miles due west of the Interstate 10 (I-10) freeway.
Cactus 110, a wholly owned subsidiary of ASCU, acquired all American Smelting and Refining Company (ASARCO) land parcels representing the project in July 2020 by executing a purchase agreement (PA) and prospective purchaser’s agreement (PPA) with a multi-state custodial trust, and the Arizona Department of Environmental Quality (ADEQ).
Subsequently, the company signed multiple agreements to acquire adjacent lands to the project.
The company’s total landholdings include an area of approximately 5,720.08 acres.
The Cactus Mine project lies is 40 road miles southeast of the Greater Phoenix metropolitan area. The site is accessible from West Maricopa Casa Grande Highway (Highway) via 2.2mile Bianco Road.
Geology and Mineralisation
The Cactus and Parks/Salyer copper projects are situated in Arizona’s Basin and Range Province—an arid region marked by significant tectonic activity. These two deposits represent segments of a larger porphyry copper system that has been structurally disrupted and offset by Tertiary-age extensional faulting.
The primary host lithologies include the Precambrian Oracle Granite along with Laramide-aged monzonite and quartz monzonite porphyries. These intrusive rocks have interacted with the older granite to form complex breccia zones—ranging from monolithic to mixed breccias—alongside large intrusive bodies, irregular dyke-like masses, and thin, discontinuous dykes.
The structural framework is notably complex, characterised by intense fracturing, multiple phases of faulting, and both pre-mineral and post-mineral brecciation. The mineralised zones are confined between major normal faults to the east and west, which have played a key role in shaping the deposit’s geometry.
Chalcocite and covellite are the primary secondary sulphides. The chalcocite blanket displays considerable variability in thickness, grade, and continuity. Leached capping ranges from less than 30m to nearly 200m thick, with the thickest sections located in the northern portion of the system. Oxidised copper minerals, including chrysocolla, brochantite, and malachite, are scattered throughout the capping in irregular concentrations.
Cactus exhibits classic hallmarks of a porphyry copper system. Copper mineralisation occurs in a network of stockwork veinlets and as fine disseminations within an altered rock matrix, reflecting the typical structural and mineralogical controls associated with porphyry-style deposits.
Mineral Resource Estimate
In July 2024, ASCU released its updated Mineral Resource Estimate (MRE) for the Cactus brownfield copper project.
The Measured and Indicated (M&I) resources are estimated at 632.6 million short tonnes, at a total copper (CuT) grade of 0.58%, amounting to approximately 7.3 billion pounds of copper.
Inferred resources are calculated at 474 million short tonnes, at a CuT grade of 0.41%. This corresponds to around 3.8 billion pounds of copper.
Mining at Cactus Project
Cactus Project will primarily source mineralised material from the Cactus West and Parks/Salyer open pits, which together account for 94% of the total feed. Cactus West has a strip ratio of 1.0:1, while Parks/Salyer stands at 3.2:1, resulting in a life-of-mine average of 2:1. Minor contributions will come from the Cactus East underground deposit (5%) and the Stockpile (1%).
Both pits will be mined on 40ft benches, using 320-tonne haul trucks. Parks/Salyer pit walls are designed with inter-ramp angles of 45°, adjusted to 40° with step-outs, while Cactus West walls average 41–43°. Waste is largely composed of Gila conglomerate and alluvium.
Parks/Salyer is expected to produce 531Mt of feed grading 0.530% CuT over 23 years, starting in Year -1. Cactus West will supply 306Mt grading 0.29% CuT during selected years to balance stripping requirements. Stockpiled material (9.8 Mt at 0.24% CuT) will support initial commissioning.
Underground mining at Cactus East will begin in Year 8 using sub-level caving, peaking at 3.9Mtpa, and producing 42 Mt at 0.83% CuT over 14 years. Material will be hauled via a vertical conveyor and supplemented by truck haulage if needed.
Processing will use heap leaching, with all material types crushed to minus ¾”, and a maximum leaching cycle of three years. Water usage is forecast at 1,200 gallons per minute, within existing permits.
The project’s mineral profile is expected to consist of 25% oxides, 50% enriched material, and 25% primary sulphides. From Year 23 onwards, operations will focus solely on primary sulphides, with an overall copper recovery rate conservatively estimated at 25%.
Mining Plan and Recovery
The Cactus Mine PEA outlines a production strategy involving four distinct areas- Parks/Salyer and Cactus West open pits, the Historical Stockpile, and Cactus East Underground.
Mining begins at Parks/Salyer with a pre-production stripping of 70 million tonnes, while 10 million tonnes from the Historical Stockpile are processed in Year 1 to support pit development and plant commissioning.
Open pit mining will maintain a rate of 140-163 million tons annually for the first decade, decreasing to 90 million tons by Year 15 and 16 million tons by Year 22 as Parks/Salyer winds down. Between Years 21-24, stockpile reclaim intensifies to facilitate Cactus West Phase 2 and 3. Mining then increases slightly to 60-70 million tons annually from Years 24-27, tapering off by Year 31.
Cactus East Underground’s sub-level caving begins in Year 8, reaching full production by Year 11, and continues for 14 years, ending in Year 21. Throughout the open pit schedule, about 200 million tons of low-grade and hypogene leach material are stockpiled and reclaimed to boost copper production, regulate feed material, and delay hypogene processing.
Material from the mine will be transported via haul truck to a crushing circuit, reducing it to a P80 size of minus ¾ inch. Post-crushing, it will be moved to agglomeration drums and stacked in 30-foot lifts on a lined heap leach pad using mobile conveyors and a radial stacker.
A dilute sulfuric acid leach solution will be applied to the top of each lift, percolating through the material to dissolve copper. The leach pad will ultimately reach a height of approximately 250ft (76m).
The pregnant leach solution will be processed in a copper SX/EW plant, initially producing up to 60,000 tons of copper cathodes annually with a PLS flow of up to 12,000 gpm. In Year 3, the electrowinning circuit will be expanded to double the plant’s capacity to 120,000 tons per year.
Contractors Involved
The Preliminary Economic Assessment (PEA) for the Cactus Mine Project was prepared by M3 Engineering & Technology, Arizona Sonoran Copper Company (ASCU), Clear Creek Associates, ALS Geo Resources, Geo-Logic Associates, AGP Mining and Samuel Engineering.
Ausenco led the coordination of the PFS activities and technical reporting. The firm was also responsible for the infrastructure and leach pad designs, as well as compiling the overall cost estimates and developing the financial model for the projects.
AGP Mining Consultants and Call & Nicholas (CNI) were engaged to define the mining methods for both underground and open-pit operations, while Samuel Engineering was tasked with developing the mineral processing and metallurgical testing framework and designing the processing facilities.
Clear Creek Associates provided oversight for drilling programmes, hydrogeological evaluations, and environmental fieldwork necessary for the PFS.
ALS Geo Resources contributed to the project by managing drilling activities and preparing the resource models.
Minefill Services was engaged to assess paste backfill options and conduct trade-off studies, although paste backfilling is not currently included in the active scope of the project.
