El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework

Cornejo, Paula; Tosdal, Richard M.; Mpodozis, Constantino; Tomlinson, Andy J.; Rivera, Orlando; Fanning, C. Mark

doi:10.1080/00206819709465258

Cited by 66 publications

(37 citation statements)

References 30 publications

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“…U-Pb zircon geochronology has confirmed that the magmatic history is characterized by multiple intrusions in the larger deposits (e.g., Cornejo et al 1997;Reynolds et al 1998;Ballard et al 2001). New ELA-ICP-MS U-Pb zircon geochronology of the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina (402·10 6 t of ore averaging 0.54% Cu and 0.64 g/t Au, D. Keough personal communication 2001), reveals that hydrothermal alteration developed around at least two distinct porphyry intrusions, emplaced a million years apart.…”

Section: Introductionmentioning

confidence: 77%

“…The short duration of intrusive activity in the immediate Farallo' n Negro district differs from most Andean porphyry Cu provinces, whereby porphyry-related mineralization was emplaced episodically throughout extended regional igneous activity that can occur over tens of millions of years (Skewes and Stern 1995;Cornejo et al 1997;Marsh et al 1997). Alternatively, magmatism may have occurred at depth below Bajo de la Alumbrera, as suggested by the occurrence of inherited zircons with ages between 9.0 and 12.7 Ma.…”

Section: Temporal Evolution Of the Farallo' N Negro Volcanic Complexmentioning

confidence: 99%

“…It is inferred that these magmas have assimilated or were partially melted from Paleozoic crystalline basement (e.g., Zentilli et al 1994;Cornejo et al 1997;Richards et al 1999).…”

Section: Late Miocene Volcanismmentioning

confidence: 99%

“…The r330 Ma ages correspond to major back-arc magmatism associated with arc development in the Frontal Cordillera during the Variscan Stage (Damm et al 1994). Inherited Paleozoic zircon populations are common in mineralized porphyry Cu intrusions of South America (e.g., Zentilli et al 1994;Cornejo et al 1997;Richards et al 1999). In spite of other radiogenic isotopic evidence that suggests minimal contamination by old crustal rocks (e.g., Tilton et al 1981;Harmon et al 1984;Pankhurst et al 1988;Walker et al 1991;Kay et al 1999), the presence of these old zircons provides clear evidence of at least some crustal interaction in the generation of porphyry Cu magmas (Richards et al 1999).…”

Section: Zircon Inheritancementioning

confidence: 99%

“…Here early mineralization immediately followed the onset of volcanism or occurred within 500,000 years. This implies that the fertility of the parental magma is not always dependent on a long-lived history (e.g., Skewes and Stern 1995;Cornejo et al 1997;Marsh et al 1997). …”

Section: Introductionmentioning

confidence: 99%

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ELA-ICP-MS U?Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu?Au deposit: implications for porphyry-related mineralization

Harris

Allen

Bryan

et al. 2004

Mineralium Deposita

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ELA-ICP-MS U-Pb zircon geochronology has been used to show that the porphyritic intrusions related to the formation of the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina, are cogenetic with stratigraphically well-constrained volcanic and volcaniclastic rocks of the Late Miocene Faralloń Negro Volcanic Complex. Zircon geochronology for intrusions in this deposit and the host volcanic sequence show that multiple mineralized porphyries were emplaced in a volcanic complex that developed over 1.5 million years. Volcanism occurred in a multivent volcanic complex in a siliciclastic intermontane basin. The complex evolved from early mafic-intermediate effusive phases to a later silicic explosive phase associated with mafic intrusions. Zircons from the basal mafic-intermediate lavas have ages that range from 8.46±0.14 to 7.94±0.27 Ma. Regionally extensive silicic explosive volcanism occurred at r8.0 Ma (8.05±0.13 and 7.96±0.11 Ma), which is co-temporal with intrusion of the earliest mineralized porphyries at Bajo de la Alumbrera (8.02±0.14 and 7.98±0.14 Ma). Regional uplift and erosion followed during which the magmatic-hydrothermal system was probably unroofed. Shortly thereafter, dacitic lava domes were extruded (7.95±0.17 Ma) and rhyolitic diatremes (7.79±0.13 Ma) deposited thick tuff blankets across the region. Emplacement of large intermediate composition stocks occurred at 7.37±0.22 Ma, shortly before renewed magmatism occurred at Bajo de la Alumbrera (7.10±0.07 Ma). The latest porphyry intrusive event is temporally associated with new orebearing magmatic-hydrothermal fluids. Other dacitic intrusions are associated with subeconomic deposits that formed synchronously with the mineralized porphyries at Bajo de la Alumbrera. However, their emplacement continued (from 7.10± 0.06 to 6.93±0.07 Ma) after the final intrusion at Bajo de al Alumbrera. Regional volcanism had ceased by 6.8 Ma (6.92±0.07 Ma).The brief history of the volcanic complex hosting the Bajo de la Alumbrera Cu-Au deposit differs from that For example, at the El Salvador porphyry copper district in Chile, magmatism related to Cu mineralization was episodic in regional igneous activity that occurred over tens of millions of years. Bajo de la Alumbrera resulted from the superposition of multiple porphyryrelated hydrothermal systems, temporally separated by a million years. It appears that the metal budget in porphyry ore deposits is not simply a function of their longevity and/or the superposition of multiple porphyry systems. Nor is it a function of the duration of the associated cycle of magmatism. Instead, the timing of processes operating in the parental magma body is the controlling factor in the formation of a fertile porphyryrelated ore system.

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Section: Introductionmentioning

confidence: 77%

Section: Temporal Evolution Of the Farallo' N Negro Volcanic Complexmentioning

confidence: 99%

“…It is inferred that these magmas have assimilated or were partially melted from Paleozoic crystalline basement (e.g., Zentilli et al 1994;Cornejo et al 1997;Richards et al 1999).…”

Section: Late Miocene Volcanismmentioning

confidence: 99%

Section: Zircon Inheritancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

ELA-ICP-MS U?Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu?Au deposit: implications for porphyry-related mineralization

Harris

Allen

Bryan

et al. 2004

Mineralium Deposita

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The Donoso copper-rich, tourmaline-bearing breccia pipe in central Chile: petrologic, fluid inclusion and stable isotope evidence for an origin from magmatic fluids

2002

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The copper-rich, tourmaline-bearing Donoso breccia pipe is one among more than 15 different mineralized breccias in the giant (>50 million metric tonnes of copper) Miocene and Pliocene Rı´o Blanco-Los Bronces copper deposit in the high Andes of central Chile. This breccia pipe, bracketed in age between 5.2 and 4.9 Ma, has dimensions of 500 by 700 m at the current surface 3,670 m above sea level. Its roots have yet to be encountered, and it is >300 m in diameter at the depth of the deepest drill holes. The Donoso breccia is, for the most part, monolithic, containing clasts of the equigranular quartz monzonite pluton which hosts the pipe. It is matrix supported, with between 5 and 25% of the total rock volume consisting of breccia-matrix minerals, which include tourmaline, quartz, chalcopyrite, pyrite, specularite, and lesser amounts of bornite andanhydrite. An open pit mine, centered on this breccia pipe, has a current production of 50,000 tonnes of ore per day at an average grade of 1.2% copper, and copper grade in the breccia matrix is significantly higher. Measured d 18 O for tourmaline and quartz from the matrix of the Donoso breccia at different levels of the pipe range from +6.9 to +12.0&, and measured dD in tourmaline ranges from -73 to -95&. Temperatures of crystallization of these minerals, as determined by the highest homogenization temperatures of highly saline fluid inclusions, range from 400 to >690°C. When corrected for these temperatures, the stable isotope data indicate that fluids from which these breccia-matrix minerals precipitated were magmatic, with d 18 O between +5.6 to +9.1& and dD between -51 to -80&. These isotopic data preclude participation of a significant amount of meteoric water in the formation of the Donoso breccia. They support a model in which brecciation is caused by expansion of magmatic fluids exsolved from a cooling pluton, and breccia-matrix minerals, including copper sulfides, precipitated from the same magmatic fluids responsible for brecciation. Sericitic alteration of clasts in the breccia was also caused by these magmatic fluids. Different types of fluid inclusions imply that several different magmatic fluids were involved in formation of the Donoso breccia. These include high-temperature, highly saline, non-boiling fluids, trapped in inclusions that homogenize by halite dissolution, which probably exsolved from a magma cooling under relatively high (>1 kbar) lithostatic pressure conditions, consistent with geologic constraints. Other high-temperature, highly saline fluids are trapped in inclusions that homogenize by vapor-bubble disappearance and are spatially associated with vapor-rich inclusions, suggesting either phase separation (boiling) or simultaneous separation of immiscible brine and vapor from a magma cooling at lower hydrostatic pressure conditions. Both types of high-temperature, highly saline fluids circulated intermittently, as pressure fluctuated between lithostatic and hydrostatic conditions because of episodes of sealing and rebrecciation.

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Discussion on "Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism" by Oyarzun et al. (Mineralium Deposita 36:794–798, 2001)

et al. 2002

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El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework

Cited by 66 publications

References 30 publications

ELA-ICP-MS U?Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu?Au deposit: implications for porphyry-related mineralization

ELA-ICP-MS U?Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu?Au deposit: implications for porphyry-related mineralization

The Donoso copper-rich, tourmaline-bearing breccia pipe in central Chile: petrologic, fluid inclusion and stable isotope evidence for an origin from magmatic fluids

Discussion on "Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism" by Oyarzun et al. (Mineralium Deposita 36:794–798, 2001)

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