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.

The Urals orogen represents the site of Palaeozoic oceanic crust creation and subsequently a zone of arc development, arc-continent collision, continent-continent collision and post-orogenic collapse. The orogen is host to a number of world-class VMS deposits in the Silurian to Devonian arc sequences but in addition is host to highly significant iron oxide deposits of both hydrothermal and orthomagmatic origin. The hydrothermal ores are developed in Palaeozoic belts associated with rift-related, dominantly mafic, largely subaerial, alkaline volcanism intruded by comagmatic stocks of varying ages, from the Late Silurian to Early Carboniferous. Volcanism, sedimentation and mineralisation all seem to be controlled by major N to NNE trending structures. Much of the mafic volcanic sequence shows hematisation, which is evidence of early oxidation of the lava-tuff packages. Mineralisation comprises massive and disseminated magnetite bodies with elevated REE and ubiquitous accessory apatite. The deposits can be huge, as for example the giant Carboniferous Kachar deposit in Kazakhstan with reserves of over a billion tonnes of >45% Fe are defined. Some of the bodies are true contact skarns developed at the interface between intrusive bodies and volcano-sediments which include limestones. Other bodies, including Kachar, are distal to any possible related intrusions and are developed within regionally extensive scapolite alteration zones. A regionally consistent pattern of early feldspar ± biotite alteration followed by ore-stage pyroxene-garnet-scapolite followed by late hydrous silicate-carbonate alteration is repeated throughout the Urals. Regionally extensive scapolitisation is common in most of the belts. Base metals are generally present in the deposits, often appearing late in the paragenetic sequence, with some bodies having near economic copper grades (0.6% Cu) and significant precious metals.

The Khetri, Alwar and Lalsot-Khankhera Copper Belts contain widespread Cii±Au±Ag±Co±Fe±REE±U mineralisation over a 150x 150 km area of Rajasthan and Haryana, NW India. Mineralisation is hosted by the mid-Proterozoic Delhi Supergroup, which comprises shallow-water, locally evaporitic, sedimentary rocks, with lesser mafic and felsic volcanic rocks. These rocks have been metamorphosed to the low- to mid-amphibolite facies, defonned into NE-SW striking, doubly-plunging folds, and intruded by numerous 1.5-1.7 Ga syntectonic granitoids and 0.75-0.85 Ga post-tectonic granitoids. Post-tectonic granitoids range from tonalite to syenite, contain hornblende and biotite as the dominant mafic minerals and magnetite, titanite, allanite, apatite, fluorite as accessory phases, and are geochemically characterised by A/CNK ratios <1.1, low Al and Ca, high Th and HFSE, and enrichment in LREE, indicating A-type affinities.

The Bafq metallogenic province in Iran contains world class Kiruna-type apatite-iron oxide ores, apatite-rich magmatic rocks called "apatitites", REE, Th-U, Pb-Zn and recently reported Cu(-Au?) mineralisation. The metallogenesis is related to magmatic events that accompanied a major late Precambrian rifting event within Gondwanaland. The magmatic activity is subvolcanic to volcanic, is characterised by thebimodal association of rhyolites and spilitic basalts and is accompanied by a regional alkali metasomatism.

The iron deposits are commonly hosted by hydrothermally altered and metasomatised rhyolitic rocks, which are either interstratified with volcano-sedimentary sequences, or form large subvolcanic and volcanic masses. The iron ore is dominantly a Ti-V-poor massive magnetite with subordinate hematite, and is commonly accompanied by apatite. Apatite also occurs within the magmatic "apatitites', which are spatially and temporally closely associated with the iron ores.

The Sin Quyen deposit in northern Vietnam is an unusual example of the Fe oxide-Cu-Au-REE group of deposits. Magnetite-orthite-chalcopyrite-gold mineralisation is hosted by extremely altered amphibolite and biotite-gneiss lenses within highly defonned and metamorphosed sediments of the Proterozoic Sin Quyen Formation. The deposit fonned in a wide fault zone which acted as a channel for pre-mineralisation amphibolite and granitic dykes, mineralising fluids as well as post mineralisation granite, pegmatite and amphibolite. Metasomatic alteration produced a variety of assemblages predominantly composed of variable amounts of quartz, hastingsite and biotite but also including small zones of hedenbergite-garnet skarn. Alteration is closely associated with magnetite and orthite (allanite) development. Sulphide mineralisation, mainly chalcopyrite and pyrrhotite with lesser pyrite is a later and lower temperature hydrothermal phase, although the majority of the sulphides were deposited within the alteration zones.

The Guelb Moghrein deposit is located within the Mauritanide Mobile Zone, north east of Nouakchott in the Islamic Republic of Mauritania, West Africa. The copper, gold and iron deposits of the Maurilanides fold/thrust belt of the Akjoujt area have many of the characteristics of the hydrothermal iron oxide copper-gold class of deposits as well as showing distinctive features of their own. Exploration by General Gold International SA since 1994 has concluded that they represent, perhaps, a carbonate-rich sub class and show considerable diversity of form and setting.

The Mauritanides in Mauritania incorporate a great diversity of rocks in multiple, thrust-bounded domains including metamorphosed siliciclastic sediments, meta-felsic volcanics, meta-basic volcanics, serpentinite, and bodies of granitoid rocks.

The Wernecke and Southern Ogilvie Mountains in Yukon are part of an almost east-west trending range in the northern Canadian Cordillera in which several areas of the Palaeo-Mesoproterozoic basement are exposed, enveloped by a Phanerozoic miogeoclinal sequence. The oldest division, the -1.8-1.4 Ga Wernecke Supergroup, is interpreted as a "clastic rift'". It is an up to 15 km thick pile, the bulk of which is a monotonous, well-bedded siltite-quartz rich litharenite-argillite, topped by carbonate-pelite units. Less than 1% of the area consists of small gabbro to diorite intrusions of several, mostly Palaeoproterozoic and Mesoproterozoic, generations. The predominantly brittle deformation regime produced extensive tracts of disrupted and dismembered units grading to tectonic (not subduction !) melange. These have been overprinted by large scale Na, Ca, Mg, Fe, C02 and lesser Si, K metasomatism to produce widespread albitisation, chloritisation, carbonatisation, hematitisation and less extensive sericitisation (with local biotite) of the fractured sedimentary » magmatic rocks as well as tectonic fragmentites. The "Wernecke Breccia" is a metasomatised disaggregated breccia series and it is associated with hundreds of small scattered showings of specular hematite, magnetite and chalcopyrite, several occurrences of U and Co minerals, and anomalous gold. Not even a marginally economic orebody has so far been discovered despite intermittent exploration going back to the 1960s. It appears that we are dealing with a moderately deep (closely above the ductile-brittle interface) level of regional release and displacement of metals from source rocks (Fe, Cu and Co from gabbros; U perhaps from carbonaceous argillites) by metasomatic destruction of the carrier minerals. However, the system lacked sufficient plumbing and the channelling required to produce better metal accumulations at higher levels.

Proterozoic hydrothermal iron oxide deposits occur within two metallogenic belts in the northeastern U.S.: the Adirondack region, and the Mid-Atlantic (Reading Prong) belt. A 175 km wide belt of Palaeozoic cover separates these two regions, although some iron deposits occur in Proterozoic rocks near the unconformity, suggesting a possible continuation beneath the cover. Although potentially part of the same continuous metallogenic province sharing similar mineralogy, host rock composition and hydrothermal alteration, deposits in the two regions differ in degree of deformation. Differences in the degree of metamorphic deformation fuel the debate of the relative timing of mineralisation, igneous activity, and metamorphism. Generally less deformed textures in the Adirondack deposits led workers in the New York deposits to conclude iron ores in the Adirondacks are associated with anorogenic granites that postdate peak metamorphism. Folded iron ores in granitic gneiss of the Mid-Atlantic belt suggest some deposits in eastern Pennsylvania, northern New Jersey, and southern New York predate peak metamorphism. REE-enriched deposits in both belts are characterised by abundant apatite, tourmaline, and manganese concentrations, as well as the presence of hematite-chlorite alteration in addition to magnetite. Unlike deposits hosted exclusively within granite gneisses, deposits within supracrustal rocks commonly contain significant sulphides and so are potential hosts for copper mineralisation.