The Pinto Valley Mine (PVM) is an operational open pit mine in the US state of Arizona that produces copper and molybdenum concentrates, and copper cathode.
The project is 100% owned by Capstone Copper, a Canada-based metals mining company, via its affiliate Pinto Valley Mining.
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The open pit development of the mine commenced in 1972 and it recorded first production in 1975. There had been intermittent shutdown in operations until 2012, and subsequently PVM operated continuously.
Since the first start of production, the mine has produced more than 4 billion pounds of copper including 0.5 billion pounds of copper cathode.
At peak, the mine has a throughput of approximately 60,000 tonnes per day (tpd).
In November 2021, Pinto Valley received a new US Forest Service Mine Plan of Operations. It is now completely permitted to operate for the current life of mine until 2039.
A district growth study is underway to evaluate a potential extension of mine life through 2050.
Pinto Valley Mine’s total (proven and probable) reserves stand at 381 million tonnes containing 2,710Mlb copper at a grading of 0.32% and 53Mlb molybdenum at a grading of 0.006%.
Pinto Valley Mine Location
The Pinto Valley Mine is located at the west end of the Globe-Miami mining district, one of the oldest and most productive US mining districts, in Central Arizona.
The mine is approximately 80 miles east of Phoenix via Highway 60.
Pinto Valley owns approximately 10 square miles of patented land and 467 unpatented mining claims around the perimeter of the patented land.
The property also includes a 27acre ranch including 33,000 acre grazing allotment located within the Tonto National Forest under the control of the US Department of Agriculture-Forest Service (USFS).
Pinto Valley Ownership and Operational History
Originally, the Pinto Valley Mine was Miami Copper Company in 1909.
In 1960, the company was purchased by the Tennessee Corporation, which merged with Cities Service Company in 1969.
The mine was owned by Cities Service Company when it was in the construction and commissioning phases.
In late 1982, Occidental Petroleum acquired Cities Service and in 1983, it sold the Miami operations to Newmont Mining. During this time, the name of the company was changed to Pinto Valley Copper Corporation.
The Pinto Valley Copper assets were merged into Magma Copper Company Holdings by Newmont in 1986, becoming Magma’s Pinto Valley Mining Division.
Broken Hill Proprietary Company bought Magma in 1995 and it merged with BHP Billiton in 2001. After Broken Hill’s merger with Billiton, the Pinto Valley Mining Division became Pinto Valley Operations of BHP.
Capstone purchased the Pinto Valley Operations in 2013.
In March 2022, Capstone Copper was formed via a transaction that combined Old Capstone and Mantos Copper (Bermuda).
After commencing operations in 1974, PVM had a brief shutdown in 1983. Operations also remained suspended between the period from 1998 to 2007, and from 2008 to 2012.
The mine has been operating continuously since 2012.
Geology and Mineralisation
In the Globe-Miami mining district, several larger mines are porphyry copper deposits associated with Paleocene (63 megaanni [Ma]–59 Ma) granodiorite to granite porphyry stocks.
Such deposits have been affected by faults, erosion and oxidation.
The primary minerals found in these deposits are pyrite and chalcopyrite. They also contain minor amounts of molybdenite, while gold and silver are recovered as by-products.
Sphalerite and galena are found locally in non-economic occurrences.
The Pinto Valley Mine deposit is a hypogene ore body and contains pyrite, chalcopyrite, and minor molybdenite as primary sulphide minerals. The primary host rock in the property is the Lost Gulch Quartz monzonite of the Precambrian age, equivalent to the Ruin Granite.
The deposit’s formation was associated with the intrusion of small bodies and dikes of granite porphyry and granodiorite.
Pinto Valley Project Reserves
According to a technical report published in 2021, PVM has total (measured and indicated) mineral resources of 1,402.3 million tonnes containing 8,934.6Mlb copper at a grading of 0.29% and 170Mlb molybdenum at a grading of 0.006%.
The mine has inferred mineral resources of 170.6 million tonnes containing 967.6Mlb copper at a grading of 0.26% and 20.7Mlb molybdenum at a grading of 0.006%.
PVM has proven probable reserves of 241.6 million tonnes containing 1,833Mlb copper at a grading of 0.34% and 35.6Mlb molybdenum at a grading of 0.007%.
The probable mineral reserves of the mine stand at 139.4 million tonnes containing 877Mlb copper at a grading of 0.28% and 17.4Mlb molybdenum at a grading of 0.006%.
Mining and Processing
Pinto Valley is mined using the conventional open-pit hard rock mining methods. The method involves drilling, blasting, loading, and hauling of ores.
The ore undergoes crushing in a primary crusher and the waste rock is stored in the waste storage facilities. The mining is conducted on 45ft benches.
The Run-of-Mine (ROM) is conveyed to a Fuller Traylor gyratory primary crusher. It crushes the ore which is then transferred to coarse ore stockpile and subsequently to the secondary and tertiary crushing circuits.
The fine crushed ore undergoes grinding in six Allis-Chalmers overflow ball mills. Water is added to the circuit to get desired percent solids content for grinding.
A bulk copper and molybdenum flotation process is used to deliver the final individual copper and molybdenum concentrates.
Total mining rates will remain 52.6Mt annually from 2021 through 2031, and then drop through to 2039.
Contractors
The Pinto Valley Mine technical report, which was published in 2021, was compiled by Capstone and Pinto Valley Mining. Wood, Global Resource Engineering, Independent Geomechanics and Kirkham Geosystems supported the preparation of the report.
WestLand Resources provided a range of environmental support services for the mine for more than 20 years and completed its contract in 2020.
