Pinto Valley

Pinto Valley is currently the only operating mill located in the historic Globe-Miami mining district of Arizona, one of the oldest and most productive mining districts in the United States. Since its first recorded production in 1975, Pinto Valley has produced more than four billion pounds of copper, including 0.5 billion pounds of copper cathode. Capstone acquired Pinto Valley from BHP Billiton in October 2013 and is currently the second-largest employer in the district contributing over $270 million annually to Arizona’s economy.

Capstone continues to optimize Pinto Valley for higher copper prices.

PV3 Optimization – Completed in 2021

The $31 million, two-year PV3 Optimization program focused on innovation and a series of low-capital, quick payback projects to debottleneck operational performance including investments in the fine crushing plant, two new ball mill shells, as well as upgrades to tailings thickeners and tailings pumping stations. The project has improved productivity and increased recoveries and mill throughput to 60,000 tpd during peaks. The mine received a new US Forest Service Mine Plan of Operations in November 2021 and is fully permitted to operate until 2039.

PV3 Optimization – Time-lapse of Ball Mill #3 Change Completed in 2021


PV4 Study – Underway and expected in Q4 2022

The PV4 Study is evaluating the mine’s long-term growth potential of Measured and Indicated Resources (inclusive of Reserves) of over 1.36 billion tonnes at 0.30% copper. The study includes a series of technological innovations including:

  • Jetti Catalytic Leach Technology: It has the potential to increase cut-off grades to the mill and increase tonnage under leach. Scenarios include increased mining rates, higher mill grades and increased leaching. A column leach test is ongoing through the first half of 2022.
  • Coarse Particle Flotation (CPF) Technology: It has the potential to increase copper recoveries by at least 6% to a total of ~90% while providing flexibility to increase mill throughput.
  • Pyrite Agglomeration: To divert acid-generating minerals including chalcopyrite from tailings to the dump leaching operations, where additional Copper can be recovered and some acid necessary for production can be generated. This is a low-capital project (~7M with a quick one-year payback).

During 2021, study work progressed on the pre-feasibility study for PV4 which aims to maximize the conversion of approximately one billion tonnes of mineral resources to mineral reserves, significantly extending Pinto Valleys mine life and increasing the mine’s copper production profile. The application of the following new technologies and innovation is being considered:

  • Expansion of the use of Jetti Catalytic Leach Technology which has the potential to increase mill cut-offgrades and increase tonnage available for leaching. Column leach testing is ongoing through H1 2022 and results will be included in the PV4 Study.
  • Pyrite Agglomeration, with strong positive environmental, social and governance ("ESG") implications as it would divert acid-generating minerals including pyrite and chalcopyrite from tailings to the dump leach operation. Additional copper recovery and lower costs via self–generation of free acid would also be key economic drivers for this project. The project’s initiation would be targeted for H2 2022 subject to board approval. Based on preliminary study results, the project is expected to require a low capex with a short payback period.

Higher mill throughput will be considered targeting up to 65,000 to 70,000 tpd. Key areas of investment include upgrades to ball mill motors, grinding circuit cyclones, and to the rougher flotation circuit and evaluation of coarse particle flotation. A low capital strategy is currently under review to improve coarse particle recovery with some modest investment in the current conventional flotation circuit. An expanded dump leach strategy would translate to higher grades sent to the mill for processing and increased copper cathode production by expanding dump leach tonnage.

Pinto Valley is also evaluating other new technologies such as Autonomous Trucking.

Geology and Mining

Geological setting Porphyry Copper Deposit - primary host rock is the Precambrian-age Lost Gulch Quartz Monzonite, (equivalent to the Oracle Granite or Ruin Granite).
Economic Mineralization Hypogene ore body with chalcopyrite, pyrite, and minor molybdenite as the significant primary sulfide minerals
Mining method Open pit
Primary product mined Copper
By-products mined Molybdenum

Technical Reports

Download item year list

Mineral Reserves & Resources

Pinto Valley Mineral Reserves, Remaining at March 31, 2021

Classification Tonnes (millions) % Cu % Mo Contained Cu (kt) Contained Mo (kt)
Proven 241.6 0.34 0.007 831 16
Probable 139.4 0.28 0.006 398 8
Total P+P 381.0 0.32 0.006 1,229 24

NOTE: The Mineral Reserve has an effective date of March 31, 2021 and was prepared by Clay Craig, P.Eng., Manager, Mining and Evaluations at Capstone Copper Corp. The economic assumptions include the following: $3.00/lb Cu and $10.00/lb Mo, 86.0% average Cu recovery, 8.5% average Mo recovery, $1.68/tonne average mining costs, $1.13/tonne G&A costs, $0.88/tonne Ops Support costs, $4.67/ton milling costs, and pit slopes by rock type. The Mineral Reserve is reported at a variable cut-off ranging from 0.17% to 0.21% copper. Tonnage measurements are in metric units. Copper and molybdenum grades are reported as percentages. Contained metal is reported as million pounds. Rounding may result in apparent summation differences between tonnes, grade and contained metal.

Pinto Valley Mineral Resource (inclusive of Mineral Reserves) at 0.14% Copper Cutoff, as of March 31, 2021

Classification Tonnes (millions) % Cu % Mo Contained Cu (kt) Contained Mo (kt)
Measured (M) 619.9 0.33 0.006 2,015 38
Indicated (I) 782.5 0.26 0.005 2,038 40
Total M & I 1,402.3 0.29 0.006 4,053 77
Inferred 170.6 0.26 0.006 439 9

NOTE: The Mineral Resource is classified according to CIM (2014) definitions, estimated following CIM (2019) guidelines and has an effective date of March 31, 2021. The Independent Qualified Person for the estimate is Mr. Garth D. Kirkham, P.Geo., FGC., Of Kirckham Geosystems Ltd. The economic assumptions include the following: $3.50/lb Cu, $10.00/lb Mo, 84.6% average Cu recovery, 8.9% average Mo recovery, $1.74/tonne average mining costs, $1.13/tonne G&A costs, $0.88/tonne operational support costs, $4.67/ton milling costs, and pit slopes by rock type. The Mineral Resource is reported inclusive of the Mineral Reserve.  The last date for drilling data and mining activities is March 31, 2021. Rounding may result in apparent summation differences between tonnes, grade and contained metal.