The Collahuasi district is located in northeastern Chile, approximately 200 km southeast of the port of Iquique. It defines an area of 1200 km2 in the Western Cordillera of the Andes Mountains, between altitudes of 4000 and 5000 m above sea level. The district hosts a cluster of mineralised centres that currently comprise three porphyry copper, associated high level epithermal vein, and palaeogravel-hosted exotic copper deposits. The Quebrada Blanca, Ujina and Rosario porphyry copper deposits are currently in production, as are the Huinquintipa exotic copper accumulations. The Collahuasi porphyry deposits are spatially associated with the West Fissure/Domeyko Fault System and appear to have been emplaced during a period of dextral transpression between 35-34 Ma.

The copper and molybdenum mineralisation of the Chuquicamata deposit has been known since the 19' century. The deposit is located within the Codelco Norte District in the Andes Ranges of northern Chile, 200 km northeast of the city of Antofagasta. Small miners initially worked the exposed oxidised outcrops and high grade oxide veins that were the surface expression of the deposit, although industrial scale mining did not commence until 1915 with open pit exploitation of the main disseminated oxides. Mining has continued to the present day, currently removing approximately 170 000 tonnes of ore and 400 000 tonnes of waste per day.

The Escondida porphyry copper deposit and its satellites are the source of ore for the world's current largest copper mine, with an installed capacity of 1.2 Mt of fine copper per annum. The published ore reserve + mineral resource at Escondida and the satellite Escondida Norte deposits at the end of 2004 totalled 2.88 Gt @ 1.13% Cu, or 10.11 Gt @ 0.70% Cu when lower grade leach and oxide ores are included. Escondida was discovered in 1981 as the culmination of an exploration program initiated in 1978. This program, the Atacama Project, was specifically targeted at locating supergene enriched porphyry copper ore within the 500 km interval between Chuquicamata and El Salvador, in the established porphyry copper belt of northern Chile.

The Bajo de la Alumbrera porphyry copper-gold deposit is located within the northern Sierras Pampeanas in the eastern Andes Mountains of northwestern Argentina. It formed in a tectonically favourable location within a major arc-oblique wrench fault system, the Tucuman Transfer Zone. Initial andesitic volcanism deposited on crystalline Lower Palaeozoic basement, and subsequently emplaced dacitic subvolcanic stocks are directly related to eastward subduction of the Nazca oceanic plate beneath the western continental margin of South America. Structural preparation and shallowing of the angle of subduction of the Nazca plate -related to the arc-normal Juan Fernandez Ridge on that plate - probably aided the ascent of calc-alkaline oceanic arc-related magma into the Tucuman Transfer Zone.

El Teniente, located in the Andes of central Chile, is the world's largest known Cu-Mo deposit with estimated resources of >75xl0 tonnes of fine Cu in ore with grades greater than 0.67%. Most of the high-grade hypogene Cu at El Teniente occurs in and surrounding multiple magmatic-hydrothermal breccia pipes. Mineralised breccia complexes, with Cu contents >1%, have vertical extents of >1.5 km, and their roots are as yet unknown. These breccias are hosted in a pervasively biotite-altered and mineralised mafic intrusive complex composed of gabbros, diabases, and porphyrinic basalts and basaltic andesites. The multiple breccias in El Teniente include Cu and sulphide-rich biotite, igneous, tourmaline and anhydrite breccias, and also magnetite and rock-flour breccias. Biotite breccias are surrounded by a dense stockwork of biotite-dominated veins which have produced pervasive biotite alteration and Cu mineralisation characterised by chalcopyrite » bornite + pyrite. Later veins, with various proportions of quartz, anhydrite, sericite, chlorite, tourmaline, feldspars and Cu and Mo sulphide minerals, formed in association with 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 Cu, but in other cases eliminated or redistributed pre-existing mineralisation. Both the Teniente Dacite Porphyry and the central rock-flour Braden Pipe breccia, the dominant litho-structural unit in the deposit, are Cu-poor. Their emplacement at a late stage in the development of the deposit created a relatively barren core, surrounded by a thin (~^i50 m) zone of bornite > chalcopyrite, in the larger main area of chalcopyrite-rich, biotite-altered mafic rocks and mineralised breccias. The small Teniente Dacite Porphyry is not the "productive" pluton responsible for the enormous amount of Cu in the deposit. Instead, the deposition of the large amount of high grade Cu, and other key features of the deposit such as the barren core, are the result of the emplacement of multiple breccias generated by exsolution of magmatic fluids from a large, long-lived, open-system magma chamber cooling and crystallising at >4 km depth below the palaeosurface. It is for this reason that genetically El Teniente, like other giant Miocene and Pliocene Cu deposits in central Chile, is best considered a megabreccia deposit. The multistage emplacement of breccias, alteration and Cu mineralisation at El Teniente spanned a time period of >2 million years, between >7.1 and 4.4 Ma. This occurred at the end of a >10 million year episode of Miocene and Pliocene magmatic activity, just prior to the eastward migration of the Andean magmatic arc as a consequence of decreasing subduction angle due to the subduction of the Juan Fernandez Ridge below central Chile. Ridge subduction and 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 Andean structures, which focused magmatic activity and mineralisation at this one locality for an extended period of time.

Three of the world's largest Cu-Mo deposits, Los Pelambres, Rio Blanco-Los Bronces and El Teniente, formed in close temporal association with southward migration of the locus of subduction of the Juan Fernandez Ridge and the resultant decrease in subduction angle below central Chile during the Miocene and Pliocene. All three contain large Cu-mineralised magmatic-hydrothermal biotite itourmaline ±anhydrite breccia pipes generated by exsolution of saline, high-temperature fluids from crystallising magmas. Sr, Nd, Pb, S, Os, 0 and H isotopic data indicate that the metals these breccias contain, and aqueous fluids responsible for their emplacement, were derived from the same magmas that produced igneous rocks associated with each deposit. Isotopic data are consistent with derivation of these magmas from subduction-modified subarc mantle, and suggest that formation of these deposits did not involve either dehydration or melting of continental crust. Each deposit formed by multiple mineralising events occurring over a >2 m.y. period during which there is no evidence for coeval volcanic activity. Assuming an average Andean magma with 100 ppm Cu, the original lOOxlO6 tonnes of Cu in each deposit prior to erosion requires a parent body of magma with a batholith-size dimension of approximately >600 km3. We suggest that the multiple Cu-mineralised breccia pipes in each deposit were generated by exsolution of magmatic fluids from the roofs of large, long-lived, open-system magma chambers, crystallising at depths of >4 km below the palaeosurface as indicated by

The Chilean Andes comprise the most richly endowed copper province on Earth. A total resource (including production) of about 490 million tonnes of fine copper has been identified in more than 63 porphyry copper deposits and numerous prospects.

Andean porphyry deposits occur along five metallogenic belts that extend from central Chile to southern Peru and northwest Argentina. They formed between the Early-Late Cretaceous and Pliocene. Within these belts the deposits occur in clusters associated with multiphase plutonic complexes. This relationship is particularly prevalent in the Late Eocene-Oligocene belt, the most prolific of all. The time span between the oldest and youngest belt corresponds to the period in which contractional tectonism of the Andean cycle was established and developed from Late Cretaceous to Recent.

This paper presents U-Pb-He triple-dating age detenninations for several porphyry Cu±Mo+Au deposits in Chile, Indonesia and Iran in an effort to determine their thermal histories and to explore the effects of cooling/exhumation rates on ore formation and preservation processes. Inverse thermal modelling of measured time-temperature history data from these deposits was conducted to quantitatively constrain the depth of emplacement, duration of ore deposition, exposure ages and cooling/exhumation rates. The duration of hypogene ore formation for the deposits studied generally occurs within timeframes of 105 years, although modelling results for the Grasberg, Batu Hijau and El Teniente super porphyry deposits suggest formation periods of the order of 104 years. Emplacement depths on intrusions associated with porphyry mineralisation range from 800 m to 5500 m from the palaeosurface, with Grasberg and Rio Blanco being respectively the shallowest and deepest super porphyry deposits studied. The thermochronology data indicates a positive correlation between metal grade and cooling rate during hypogene ore formation, but further investigation is warranted. Exhumation rates varying from 0.3 to 1.1 km/m.y. have implications for the preservation potential of hypogene ore deposits, with super porphyry deposits like Sar Cheshmeh potentially losing 3.5 Mt of copper to erosion over the last 5 million years. The potential for supergene ore formation under such conditions is high, as is the potential for the formation of proximal Exotica-type deposits.

The formation of porphyry Cu deposits in calc-alkaline magmatic arcs is considered to be the cumulative product of a wide range of processes beginning with dehydration of the subducting oceanic slab. No single process is key to the formation of large deposits, but the absence or inefficient operation of any contributory process, or the action of a deleterious process, can stunt or prevent deposit formation.

Geophysics is an essential part of most modern mineral exploration programs for iron oxide copper-gold deposits. This paper reviews the important physical properties, which are the basis for the application of geophysical methods, and attempts to illustrate and summarise the ways they have been applied with data and images from selected deposits. Some comments are provided on their historical effectiveness and the role of these methods in an overall program, which must use all available data from geology, mineralogy, geochemistry and geophysics.