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Pinto Valley, Castle Dome |
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Arizona, USA |
| Main commodities:
Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Pinto Valley hypogene porphyry copper deposit and Castle Dome supergene orebody lie on the western periphery of the Globe-Miami district in south-eastern Arizona (#Location: 33° 24' 31", 110° 58' 5"W).
For detail of the setting and district geology, see the separate Globe-Miami District record.
The Pinto Valley deposit is almost exclusively composed of hypogene ore and lies below the old Castle Dome supergene orebody which was exhausted in 1953. The ore is primarily hosted by the 1400 Ma Lost Gulch Quartz Monzonite and to a lesser extent by the two phase Laramide Schultz Granite. All of these intrusives cut the Palaeoproterozoic Pinal Schists, an 1100 Ma dolerite mass and Devonian carbonates within the pit. None of these latter lithologies have been significantly mineralised, although the carbonate has been extensively altered to skarn.
The annular orebody, which plunges to the north at around 45°, surrounds a barren core characterised by a high density of un-mineralised quartz veining. The orebody comprises stockwork veinlet and disseminated sulphide mineralisation, with chalcopyrite, pyrite and minor molybdenite as the only
significant primary sulphide minerals. These are associated with biotite rich potassic alteration, which are overprinted by pyritic veins with associated phyllic selvages. Hypogene mineralisation has been dated at 59.1 ± 0.5 Ma (Creasy, 1980).
The Pinto Valley deposit is located in a horst, bounded to the west and east by outward dipping normal faults. The uplift of the horst is believed to have kept pace with chemical weathering, although the age of that weathering is not well constrained by field evidence. Petersen (1962) reported that the top of the supergene mineralisation conformed closely to the pre-mine topography.
Immediately to the west of Pinto Valley, in the Cactus-Carlotta copper deposit, there is evidence of at least two cycles of weathering and enrichment. The Cactus-Carlotta deposit is hosted by a breccia which is believed to be the product of a large landslide of Pinal Schist containing partially oxidised veinlets and disseminations of pyrite from the upper parts of the Pinto Valley mineralised system. The copper at Cactus-Carlotta is thought to have been introduced by supergene solutions derived from weathering of the Pinto Valley sulphide mineralisation, which percolated through the breccia and precipitated as chalcocite partially replacing the original pyrite within the breccia. These supergene sulphides were subsequently oxidised to chrysocolla and 'copper-wad'. The Cactus-Carlotta mineralisation is overlain by the Early-Miocene (ca. 17 to 20 Ma) Apache Leap Tuff. Some copper mineralisation is found in the base of the Apache Leap Tuff, indicating that at least some of the supergene mineralisation is Late Miocene.
Production + reserves/resources at the Pinto Valley and Castle Dome deposits in 1996 (advised during mine visit) totalled:
1370 Mt @ 0.32% Cu.
Remaining mineral resources and ore reserves at 30 June, 2012 (BHP Billiton, 2012) were:
Total measured + indicated + inferred resources at Pinto Valley
sulphides - 191 Mt @ 0.4% Cu,
low grade leach - 78 Mt @ 0.19% Cu,
sulphide stockpile - 448 Mt @ 0.11% Cu,
Total measured + indicated + inferred resources at Pinto Miami
in situ leach - 214 Mt @ 0.31% Cu,
Total proved + probable reserves (included in resources) at Pinto Valley
sulphides - 75 Mt @ 0.4% Cu,
low grade leach - 13 Mt @ 0.21% Cu.
Since 2014, Pinto Valley Mine has produced 0.43 Mt of copper.
Remaining NI 43-101 compliant Mineral Resources and Ore Reserves as at 31 March, 2021 (Capstone Mining Corp, 2021) were:
Proved Ore Reserves - 241.6 Mt @ 0.34% Cu, 0.007% Mo;
Probable Ore Reserves - 139.4 Mt @ 0.28% Cu, 0.006% Mo;
Proved + Probable Ore Reserves - 381.0 Mt @ 0.32% Cu, 0.006% Mo;
Measured Mineral Resources - 619.9 Mt @ 0.33% Cu, 0.006% Mo;
Indicated Mineral Resources - 782.5 Mt @ 0.26% Cu, 0.006% Mo;
Measured + Indicated Mineral Resources - 1402.3 Mt @ 0.29% Cu, 0.006% Mo;
Inferred Mineral Resources - 170.6 Mt @ 0.26% Cu, 0.006% Mo.
Since its first recorded production in 1975, the Pinto Valley Mine has produced more than 1.8 Mt of copper, including 0.227 Mt of copper cathode.
Ownership of Pinto Valley Mines has changed numerous times since its inception. It originated as the Miami Copper Company in 1909, to be acquired by the Tennessee Corporation in 1960. In 1969, Cities Service Company merged with the Tennessee Corporation at the time of construction and commissioning at Pinto Valley. Occidental Petroleum Corporation acquired the Cities Service Company in late 1982 and sold the Miami operations to Newmont Mining Corporation in 1983, at which time, the company's name was changed to Pinto Valley Copper Corporation. In 1986, Newmont merged the Pinto Valley Copper assets into Magma Copper Company Holdings, when it became the Pinto Valley Mining Division of Magma Copper Company. In 1995, Broken Hill Proprietary Company Limited purchased Magma Copper Company. With the merger of Broken Hill Proprietary and Billiton in 2001, the Pinto Valley Mining Division became Pinto Valley Operations of BHP Billiton. In 2013, Capstone affiliate-PVMC purchased the Pinto Valley Operations, now referred to as the Pinto Valley Mine or the Capstone Pinto Valley mine.
Development at Pinto Valley began in 1972 and the concentrator went into production in 1974. The SX-EW plant began processing leach solution from the leach dumps in 1981. A short shutdown occurred in 1983. In February 1998, mining and milling operations were suspended. The mine has had two restarts since the 1998 shutdown. It resumed sulphide operations in mid-2007 for 18 months to January 2009 and then went into care and maintenance with only
leaching operations continuing. The second restart began in December 2012 and included extensive rehabilitation of the site and purchase of a new mining fleet. During financial year ending June 30, 2013, sulphide mining resumed at Pinto Valley with production for financial year ending June 30, 2013 of 16.6 kt of copper concentrate and 4.9 kt of copper cathode.
The most recent source geological information used to prepare this decription was dated: 2004.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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| References in PGC Publishing Books: | |
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Cook S S and Porter T M, 2005 - The Geologic History of Oxidation and Supergene Enrichment in the Porphyry Copper Deposits of Southwestern North America, in Porter T M, (Ed), Super Porphyry Copper and Gold Deposits: A Global Perspective, v1 pp 207-242
 Abstract
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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