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.

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.

Within Peru, Fe oxide-Cu-Au deposits are found mainly in the Western Andes range and on the coast, associated with the Jurassic-Cretaceous alkaline to calc-alkaline volcanism of the aborted ensialic Canete-Huarmey Marginal Basin. They also exist in the calc-alkaline plutons of the Coastal Batholith and theTholeiite Patap Super-unit, associated with continental margin processes. The exception is Cobriza (100 million tonnes' @ 1.5% Cu, Fe oxide-Cu-Au type; Cu calcic distal skarn) existing in the eastern range associated with Permian Tardihercynian distensive tectonics and alkaline granites.

Porphyry-style Cu-Au/Mo deposits are among the most sought after targets for both base and precious metal exploration in the world today. Of particular interest are the "super porphyry" copper and or gold deposits, because of their size, grade and ability to support large scale, long life, profitable operations.

The term "super porphyry" is interpreted loosely in this publication, relating in general to the largest deposits in any established porphyry province. For a discussion of the accepted terminology and size classification of large porphyry-style deposits, see the introduction section of Richards, (2005) in this publication.

Porphyry-style Cu-Au/Mo deposits are among the most sought after targets for both base and precious metal exploration in the world today. Of particular interest are the "super porphyry" copper and/or gold deposits, because of their size, grade and ability to support large scale, long life, profitable operations.

The term "super porphyry" is interpreted loosely in this publication, relating in general to the largest deposits in any established porphyry province. For a discussion of the accepted terminology and size classification of large porphyry-style deposits, see the introduction section of Richards, (2005) in this publication.

This preface presents the background to this book, the second volume of the "Hydrothermal Iron Oxide Copper-Gold & Related Deposits - A Global Perspective" series, and briefly discusses the rationale for inviting the papers it contains, their format and what it is hoped the volume will achieve. It also offers some observations on the unifying characteristics of the iron oxide copper-gold family of deposits and what they may represent in a broader context.

The "hydrothermal iron-oxide copper-gold" (IOCG) family and related deposits continue to attract keen interest, both as the subject of academic research and as arguably the most sought after mineral exploration target in the world today.

Following the discovery of the giant Olympic Dam ore deposit in 1975, a realisation developed that there was an important class of mineral deposits not previously appreciated. It became apparent that this class, the Iron Oxide Copper-Gold deposits, included not only Olympic Dam, but also a number of other known deposits. It also became apparent that this was a class that could produce large, high grade prizes, of the order of 0.25 to 1 billion tonnes of around +1% Cu and 0.5 g/t Au. As a consequence this class has been one of the major targets of the exploration industry over the last decade, resulting in the discovery of further giant orebodies in Australia such as Ernest Henry, and Candelaria, Salobo, Sossego and others in South America.

Abstract - Hydrothermal copper & gold deposits associated with felsic intrusives, particularly porphyry related and epithermal ores, are found in a series of extensive, narrow, linear metallogenic provinces throughout the world. These are predominantly associated with the great Mesozoic to Cainozoic orogenic belts. Major deposits however, are also found within Palaeozoic orogens, while a few are known from the Precambrian. The style and setting of these deposits is variable and diverse, although many common features emerge from a global comparison.

Чайский массив впервые был обследован и описан в 1952 г. коллективом геологов под руководством А А Малышева, но ультраосновные породы обнаружены не 6i>uih. Сульфидное медно-никелевое оруденение было открыто В.П.Сафроновым в 1962 г. С этого времени и до 1968 г. на месторождении проводились геолого-разведочные работы, в результате которых Чайское месторождение было отнесено к категории забалансовых. Изучение месторождения связано с именами геологов Бурятского геологического управления И.Ф.Баинова, Ю.А.Чешенко, Е.В.Викулова, Л.И.Якимова, В.П.Бушуева, А.Г.Степииа и др. Большой вклад в изучение Чаиского гипербазнт-базитового массива и одноименного месторождения внесли сотрудники различных научно-исследовательских организаций - института “Гипроникель” Н.Н.Шишкин, Е.А.Кумпан (1964, 1974), ЦНИ1ТИ-А.В.Касьянов, БурятскогофилиалаСО АН СССР - С.А.Гурулее (1968, 1972, 1979), М.Ф.Труне-ва (1979) идр., ИГиГСО АН СССР Ф.ПЛоснов (1972). С начала 70-х гг. наступил большой перерыв в изучении Чайского месторождения, которое возобновилось в 1984 г. сотрудниками Геологического института БФ СО АН СССР под научным руководством Э.Г.Коннико-ва, а с 1986 по 1989 г. проводился второй этап геологоразведочных рабог силами Северо-Байкальской ГРЭ иод руководством А.Г.Степииа. В результате этих работ были существенно уточнены представления о геологическом строении массива, его формационной принадлежности, минералогии пород и руд массива, предложена новая генетическая модель формирования сульфидного медно-никелевого оруденения.

Удокан относится к типу медистых песчаников, являющихся одним из главнейших среди всех (а их около 10) промышленно-генетических представителей медных месторождений. По своим параметрам, составу, строению и экономическим показателям Удоканскос месторождение находится в ряду уникальных объектов. Открытие месторождения в 1949 г. Е.И.Буровой, К.К.Денисовым в центральной части Удоканского хребта послужило огромным толчком для проведения в этом регионе обширных геологических работ: съемок различного масштаба, поисков, оценки и разведки многих полезных ископаемых, в первую очередь меди, редких металлов, железа, угля, стройматериалов, подземных и минеральных иод. В результате всех видов исследований к настоящему времени на севере Читинской области, в пределах Кодаро-Удоканской зоны, фактически доказано и обосновано выделение медоносного пояса, являющегося дополнением к тем рудным поясам, которые были установлены в 30-40-х гг. С.С.Смирновым на территории Южного и Центрального Забайкалья. В истории изучения Удоканского месторождения, меденосного пояса и забайкальского севера выделяется несколько основных этапов, в которых отразились героизм и драматизм развития нашей геологии, промышленности, да и всей истории СССР и России. Подробная характеристика указанных этапов дана в специальной статье (Трубачев, 1993).