Porphyry copper deposit
Porphyry copper deposits are
The first mining of low-grade copper porphyry deposits from large open pits coincided roughly with the introduction of steam shovels, the construction of railroads, and a surge in market demand near the start of the 20th century. Some mines exploit porphyry deposits that contain sufficient gold or molybdenum, but little or no copper.
Porphyry copper deposits are currently the largest source of copper ore.
Geological overview
Geological background and economic significance
Porphyry copper deposits represent an important resource and the dominant source of copper that is mined today to satisfy global demand.[6] Via compilation of geological data, it has been found that the majority of porphyry deposits are Phanerozoic in age and were emplaced at depths of approximately 1 to 6 kilometres with vertical thicknesses on average of 2 kilometres.[6] Throughout the Phanerozoic an estimated 125,895 porphyry copper deposits were formed; however, 62% of them (78,106) have been removed by uplift and erosion.[6] Thus, 38% (47,789) remain in the crust, of which there are 574 known deposits that are at the surface.[6] It is estimated that the Earth's porphyry copper deposits contain approximately 1.7×1011 tonnes of copper, equivalent to more than 8,000 years of global mine production.[6]
Porphyry deposits represent an important resource of copper; however, they are also important sources of gold and molybdenum – with porphyry deposits being the dominant source of the latter.
There also appear to be discrete time periods in which porphyry deposit formation was concentrated or preferred. For copper-molybdenum porphyry deposits, formation is broadly concentrated in three time periods:
Magmas and mantle processes
In general, the majority of large porphyry deposits are associated with
The magmas responsible for porphyry formation are conventionally thought to be generated by the
After dehydration, solute-rich fluids are released from the slab and metasomatise the overlying
Tectonic and structural controls
Although porphyry deposits are associated with
Porphyry deposits are commonly developed in regions that are zones of
Arc reversal has been shown to slightly pre-date the formation of porphyry deposits in the south-west Pacific, after a collisional event.[13] Arc reversal occurs due to collision between an island arc and either another island arc, a continent, or an oceanic plateau.[11] The collision may result in the termination of subduction and thereby induce mantle melting.[11]
Porphyry deposits do not generally have any requisite structural controls for their formation; although major faults and lineaments are associated with some.[11][14] The presence of intra-arc fault systems are beneficial, as they can localize porphyry development.[9] Furthermore, some authors have indicated that the occurrence of intersections between continent-scale traverse fault zones and arc-parallel structures are associated with porphyry formation.[9] This is actually the case of Chile's Los Bronces and El Teniente porphyry copper deposits each of which lies at the intersection of two fault systems.[14]
It has been proposed that "misoriented" deep-seated faults that were inactive during magmatism are important zones where porphyry copper-forming magmas stagnate allowing them to achieve their typical igneous differentiation.[15] At a given time differentiated magmas would burst violently out of these fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed.[15]
Characteristics
Characteristics of porphyry copper deposits include:
- The orebodies are associated with multiple intrusions and dikes of diorite to quartz monzonite composition with porphyritic textures.
- Breccia zones with angular or locally rounded fragments are commonly associated with the intrusives. The sulfide mineralization typically occurs between or within fragments. These breccia zones are typically hydrothermal in nature, and may be manifested as pebble dikes.[16]
- The deposits typically have an outer epidote – chlorite mineral alteration zone.
- A quartz – sericite alteration zone typically occurs closer to the center and may overprint.
- A central potassic zone of secondary biotite and orthoclase alteration is commonly associated with most of the ore.
- Fractures are often filled or coated by sulfides, or by quartz veins with sulfides. Closely spaced fractures of several orientations are usually associated with the highest grade ore.
- The upper portions of porphyry copper deposits may be subjected to supergene enrichment. This involves the metals in the upper portion being dissolved and carried down to below the water table, where they precipitate.
Porphyry copper deposits are typically mined by open-pit methods.
Notable examples
Mexico
- Cananea
- La Caridad
- Santo Tomas
Canada
Chile
- Cerro Colorado[9]
- Chuquicamata
- Collahuasi[9]
- Escondida
- El Abra[9]
- El Salvador[9]
- El Teniente
- Los Pelambres[9]
- Radomiro Tomić
Peru
- Toquepala
- Cerro Verde, southeast of the city of Arequipa
United States
- Ajo, Arizona
- Bagdad, Arizona
- Berkeley Pit, Butte, Montana
- Bingham Canyon Mine, Utah
- Lavender Pit, Bisbee, Arizona
- Morenci, Arizona
- Pebble Mine, Alaska
- Safford Mine, Safford, Arizona
- San Manuel, Arizona
- Sierrita, Arizona[17]
- Resolution Copper, Superior, Arizona
- El Chino, Santa Rita, New Mexico
- Ely, Nevada
- Ray Mine, Arizona[18]
Indonesia
- Batu Hijau, Sumbawa
- West Papuaat >3 billion tonnes at 1 ppm Au, is one of the world's largest and richest porphyry deposits of any type
- Tujuh Bukit, Java, still under exploration, but likely to be bigger than Batu Hijau[19]
- Sungai Mak and Cabang Kiri, Gorontalo, at 292 million tonnes at 0.50 ppm gold and 0.47% copper[20]
Australia
- Cadia-Ridgeway Mine, New South Wales, copper-gold deposit mined by open pit and block caving.
- ppmAu.
Papua New Guinea
Other
- Coclesito, Panama[21]
- Majdanpek mine, Serbia[9]
- Oyu Tolgoiis one of the world's largest and richest Cu porphyry deposits, Mongolia
- La Caridad, Sonora, Mexico
- Dizon, Philippines[9]
- Saindak Copper Gold Project, Pakistan[22]
Porphyry-type ore deposits for other metals
Copper is not the only metal that occurs in porphyry deposits. There are also porphyry ore deposits mined primarily for molybdenum, many of which contain very little copper. Examples of porphyry molybdenum deposits are the Climax, Urad, Mt. Emmons, and Henderson deposits in central Colorado; the White Pine and Pine Grove deposits in Utah;[23][24] the Questa deposit in northern New Mexico; and Endako in British Columbia.
The US Geological Survey has classed the
Some porphyry copper deposits in oceanic crust environments, such as those in the Philippines, Indonesia, and Papua New Guinea, are sufficiently rich in gold that they are called copper-gold porphyry deposits.[26]
References
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- ^ "Archived copy" (PDF). www.mawsonwest.com.au. Archived from the original (PDF) on 7 March 2010. Retrieved 12 January 2022.
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: CS1 maint: archived copy as title (link) - ^ a b c d e Kesler, S.E. and B.H. Wilkinson, Earth's copper resources estimated from tectonic diffusion of porphyry copper deposits, Geology, 2008, 36(3): pp. 255–258. Abstract
- ^ a b c d e f g h Richards, J.P., Tectono-Magmatic Precursors for Porphyry Cu-(Mo-Au) Deposit Formation. Economic Geology, 2003. 98: pp. 1515–1533.
- ^ a b c d e f g h i j k l m n Cooke, D.R., P. Hollings, and J.L. Walshe, Giant Porphyry Deposits: Characteristics, Distribution, and Tectonic Controls. Economic Geology, 2005. 100(5): pp. 801–818.
- ^ a b c d e f g h i j Sillitoe, R.H., "Porphyry Copper Systems". Economic Geology, 2010. 105: pp. 3–41.
- ^ Müller D., Groves D.I. (2019) Potassic igneous rocks and associated gold-copper mineralization (5th ed.). Mineral Resource Reviews. Springer-Verlag Heidelberg, 398 pp
- ^ a b c d e f Sillitoe, R.H., Characteristics and controls of the largest porphyry copper-gold and epithermal gold deposits in the circum-Pacific region. Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia 1997. 44(3): pp. 373–388.
- ^ Sillitoe, R.H. Major regional factors favoring large size, high hypogene grade, elevated gold content and supergene oxidation and enrichment of porphyry copper deposits. in Porphyry and hydrothermal copper and gold deposits: A global perspective. 1998. Glenside, South Australia: Australian Mineral Foundation.
- ^ Solomon, M., Subduction, arc reversal, and the origin of porphyry copper-gold deposits in island arcs. Geology, 1990. 18: p. 630-633.
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- ^ Tujuh Bukit – Indonesia | Intrepid Mines[permanent dead link]
- ^ "PT BUMI RESOURCES TBK : Stock Market News and Information | BUMI| ID1000068703 | MarketScreener". 5 September 2023.
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- ^ Keith, J.D., Shanks III, W.C., Archibald, D.A., and Farrar, E., 1986, Volcanic and Intrusive History of the Pine Grove Porphyry Molybdenum System, Southwestern Utah: Economic Geology, v. 81, pp. 553–587
- ^ Jensen, Collin (2019). Multi-Stage Construction of the Little Cottonwood Stock, Utah: Origin, Intrusion, Venting, Mineralization, and Mass Movement (MS thesis). Brigham Young University.
- ^ Bruce L. Reed (1986) Descriptive model of porphyry Sn, in Mineral Deposit Models, US Geological Survey Bulletin 1693, p.108.
- ^ R. L. Andrew (1995) Porphyry copper-gold deposits of the southwest Pacific, Mining Engineering, 1/1995, pp. 33–38.
- Dennis P. Cox, 1986, "Descriptive model of porphyry Cu," in Mineral Deposit Models, US Geological Survey, Bulletin 1693, p. 76, 79.
- Michael L. Zientek, et al., 2013, Porphyry copper assessment of Southeast Asia and Melanesia, US Geological Survey, Scientific Investigations Report 2010-5090-D.