Abstract Combined isotopic dating indicates five episodes of felsic intrusion within the El Teniente orebody: (1) Sewell stock and other quartz diorite-tonalite intrusions of the eastern part crystallized from 6.46 ± 0.11 to 6.11 ± 0.13 Ma (zircon U-Pb); (2) quartz diorite-tonalite, immediately southeast of the orebody, with biotite 40 Ar/ 39 Ar plateau ages of 5.63 ± 0.12 and 5.47 ± 0.12 Ma—these ages agree with a hydrothermal overprint on zircons from the intrusions of the previous episode at 5.67 ± 0.19 to 5.48 ± 0.19 Ma (U-Pb); (3) Teniente dacite porphyry crystallized at 5.28 ± 0.10 Ma (zircon U-Pb); (4) a dacite ring dike encircling the Braden pipe crystallized at 4.82 ± 0.09 Ma (zircon U-Pb); and (5) minor dacite intrusions and dikes yielded a biotite 40 Ar/ 39 Ar plateau age of 4.58 ± 0.10 Ma, and sericite 40 Ar/ 39 Ar plateau ages of 4.56 ± 0.12 to 4.46 ± 0.10 Ma. All these felsic intrusions were emplaced within country rocks of late Miocene according to an apatite fission-track age of 8.9 ± 2.8 Ma for a mafic sill, in accord with previous K-Ar ages of 12.0 ± 0.7 to 6.6 ± 0.4 Ma for volcanic rocks from the district. Molybdenite Re-Os dating at El Teniente revealed ore deposition at 6.30 ± 0.03, 5.60 ± 0.02, 5.01 to 4.96, 4.89 ± 0.08 to 4.78 ± 0.03, and 4.42 ± 0.02 Ma, concurrent with the five intrusive episodes. The Re-Os system for molybdenite was unaffected by the various hydrothermal episodes. In contrast, the 40 Ar/ 39 Ar system of micas was reset by high-temperature (>350°C) fluid circulation and provides only a partial record of the latest history of development of this supergiant ore-forming system; biotite, sericite, and altered whole-rock samples collected throughout the orebody yielded 40 40 Ar/ 39 Ar plateau ages ranging from 5.06 ± 0.12 to 4.37 ± 0.10 Ma. These ages reveal a period of hydrothermal activity, which extended either continuously or episodically, for at least 0.69 ± 0.22 m.y. (±2σ) and that comprises a succession of three episodes of ore deposition. Separate hydrothermal episodes are thus interpreted to have lasted <0.69 ± 0.22 m.y. The Braden breccia pipe in the center of the deposit was formed as a single synmineralization event, probably related in time to the injection of the dacite ring dikes at 4.82 ± 0.09 Ma (zircon U-Pb). It was followed by quartzsericite alteration within and peripheral to, the pipe from 4.81 ± 0.12 to 4.37 ± 0.10 Ma (sericite 40 Ar/ 39 Ar). The successive intrusions of felsic bodies and their respective crystallization processes were immediately followed by genetically related, short-lived episodes of ore deposition, each associated with hydrothermal alteration. This multistage evolution, inferred from systematic dating, was not apparent from previous geochronologic data and is inferred to have contributed to the enormous volume and richness of the El Teniente. Thermal modeling of apatite fission-track data suggests that the porphyry system cooled very rapidly to temperatures below 105° ± 20°C, most likely before the intrusion of a postore hornblende-rich andesitic dike at 3.85 ± 0.18 Ma (hornblende 40 Ar/ 39 Ar). This dike cuts the southern part of the El Teniente deposit and marks the end of igneous activity in the orebody.

Abstract The giant El Teniente copper-molybdenum deposit, located in the Andes of central Chile, is one of the world's largest known copper deposits, containing estimated resources of >75 × 10 6 t of fine copper in ore with grades greater than 0.67 percent. El Teniente has been described in the past as a porphyry deposit developed around a Pliocene dacite porphyry stock, with 80 percent of its copper mineralization hosted in Miocene andesites. However, new mapping—both regional and in underground mine workings—along with petrological studies, indicates that El Teniente, like the other giant Miocene and Pliocene copper deposits in central Chile, is actually best classified as a breccia deposit. Most of the high-grade hypogene copper at El Teniente occurs in and surrounding multiple magmatic-hydrothermal breccia pipes. Mineralized breccia complexes, with copper content >1 percent, have vertical extents of >1.5 km, and their roots are as yet unknown. These breccias are hosted in a pervasively biotite-altered and mineralized mafic intrusive complex composed of gabbros, diabases, and porhyritic basalts and basaltic andesites, and not in andesite extrusive rocks. The multiple breccias in El Teniente include copper- and sulfide-rich biotite, igneous, tourmaline, and anhydrite breccias, generated by the exsolution of magmatic fluids from cooling plutons, and also magnetite and rock-flour breccias. Surrounding biotite breccias, a dense stockwork of biotite-dominated veins has produced pervasive biotite alteration, and copper mineralization characterized by chalcopyrite >> bornite + pyrite. Later veins, with various proportions of quartz, anhydrite, sericite, chlorite, tourmaline, feldspars, and copper sulfide minerals, formed in association with the emplacement of younger breccias and felsic porphyry intrusions. These generated sericitic alteration in the upper levels of the deposit, and in some cases contributed more copper to the deposit, but in other cases eliminated or redistributed preexisting mineralization. Both the Teniente Dacite porphyry and the central rock-flour breccia of the Braden pipe, the dominant lithostructural unit in the deposit, are copper poor. Their emplacement at a late stage in the development of the deposit created a relatively barren core, surrounded by a thin (~150-m) zone of bornite > chalcopyrite, in the larger main area of chalcopyrite-rich, biotitealtered mafic rocks and mineralized breccias. The multistage development of breccia emplacement, alteration and copper mineralization at El Teniente occurred over a time span that was greater than 2 m.y., between >6.4 and 4.4 Ma, at the end of a more than 10-m.y. episode of Miocene and Pliocene magmatic activity, and just prior to the eastward migration of the Andean magmatic arc as a consequence of decreasing subduction angle. Decreasing subduction angle also caused crustal thickening, uplift and erosion, resulting in telescoping of the various breccias and felsic intrusions in the deposit. El Teniente is located at the intersection of major north-south, northwest-southeast, and northeast-southwest Andean structures, but what actually focused magmatic activity and mineralization at this one locality for so long remains an unsolved problem, the solution of which would provide an important tool for exploration of similar giant deposits.

Abstract Porphyry Cu deposits commonly contain critical and precious metal by-products, including the chalcophile and siderophile elements, Au, Pd, Pt, Ag, Te, Se, and Bi. These elements partition into residual sulfides during the partial melting of mantle wedge peridotite during subduction, potentially depleting the source magma for subduction-related porphyry Cu deposits. The chalcophile-rich residual sulfides in subduction-modified subcontinental lithosphere are thought to be the source of metals in postsubduction porphyry Cu deposits, and as such these deposits may be more enriched in chalcophile and siderophile elements than subduction-related porphyry deposits, although many postsubduction deposits have low Au grades. We test this by presenting whole-rock assay and PGE data with in situ LA-ICP-MS trace element data from sulfide minerals from three porphyry Cu deposits. The Skouries Cu-Au-(PGE) porphyry deposit, Greece, and the Muratdere Cu-Au-Mo porphyry deposit, Turkey are both postsubduction; these are contrasted with the El Teniente Cu-Mo porphyry deposit, Chile, which is a classic subduction-related system. By comparing these results with a newly compiled global dataset of trace element concentrations in sulfides from 18 other porphyry Cu deposits we show that postsubduction porphyry Cu deposit sulfides are relatively enriched in Bi, Sb, Te, and Se compared to sulfide minerals from subduction-related deposits. However, although some critical and precious metals (Ag, Bi, and Se) mainly reside in primary sulfide ore minerals, others (Au, Te, Pd, and Pt) are predominantly hosted in minor accessory minerals. Whole-rock data from mineralized samples show that although the Skouries and Muratdere deposits are enriched in Au compared with El Teniente, globally both subduction-related and postsubduction deposits can be precious and critical metal enriched, with metal endowment independent of tectonic setting. PGE-enriched porphyry Cu deposits are also enriched in Bi, Te, and Au, and semimetal melts are suggested to play an important role in PGE transport and concentration in porphyry Cu deposits.