Richard H. Sillitoe

Intrusion-related gold deposits

A broad spectrum of gold mineralization styles is found in the epizonal intrusive environment, and a number of these give rise to world-class gold deposits (Figure 6.1). Here the spectrum is subdivided into: (a) intrusion-hosted stock-work/disseminated deposits of both porphyry and non-porphyry types, the former possessing all the essential geological attributes (especially multidirectional stock-works) of typical porphyry copper and/or molybdenum deposits; (b) skarn and non-skarn replacement deposits in carbonate wallrocks; (c) stockwork, disseminated and replacement deposits in non-carbonate wallrocks; (d) wallrock-hosted breccia pipes; and (e) veins in both intrusions and wallrocks. This spectrum of deposits is transitional upwards to the volcanic-hosted, epithermal gold environment, which is mentioned only briefly in this chapter but discussed at length by Henley (this volume).

Erosion and collapse of volcanoes: Causes of telescoping in intrusion-centered ore deposits

Telescoping is the process of juxtaposing or overprinting early, deep mineralization, commonly of porphyry type, and late, shallow, generally epithermal styles of precious- and base-metal mineralization. Telescoping is attributed to synhydrothermal degradation of volcanic paleosurfaces, as a result of either rapid erosion under pluvial conditions or sector (and, less probably, caldera) collapse of the volcanic edifices. Paleosurfaces may be lowered easily by 1 km during the ∼1 m.y. total life spans of hydrothermal systems, leading to the vertical compression of any contained ore deposits by at least 1 km. Sector collapse may be triggered by volcanic tumescence due to synmineralization intrusion, and it may be facilitated by hydrothermal weakening of volcanic edifices. Sector collapse causes extensive ingress of meteoric and/or ocean water to the magmatic environment and a decrease in confining pressure. The latter may induce hydrothermal brecciation, boiling and possible epithermal Au precipitation, and even accelerated efflux of magmatic fluids. Telescoped systems are believed to possess greater potential for the existence of both porphyry-type deposits at shallower than normal depths and giant ore deposits.

Epochs of intrusion-related copper mineralization in the Andes

Abstract Seventy-four copper deposits and prospects related intimately to intrusive activity in the Andes have been dated radiometrically during the last 18 years by many different investigators, most of whom used the KAr method. The results are summarized and some of their local and regional implications are reviewed. A number of copper deposits, mainly of the porphyry type, were emplaced in, or near to, premineral volcanic sequences and (or) equigranular plutons. Such precursor volcanism lasted for as long as 9 Ma, and preceded mineralization by intervals of from less than 1 Ma to as much as 9 Ma. Precursor plutons were emplaced no more than 2 to 3 Ma prior to mineralization at several localities in Chile, but possibly as long as 10 to 30 Ma earlier in parts of Colombia and Peru. The time separating emplacement of progenitor stocks and hydrothermal alteration and accompanying copper mineralization, and the duration of alteration-mineralization sequences generally are both less than the analytical uncertainty of the KAr method. However, on the basis of a detailed study of the Julcani vein system in Peru and less clearcut evidence from elsewhere, it may be concluded that alteration and copper mineralization followed stock or dome emplacement by substantially less than 1 Ma and lasted for 0.5 to 2 Ma and, locally, possibly as long as 3 Ma. At several localities, post-mineral magmatic activity could not be separated by the KAr method from the preceding alteration-mineralization events. As many as nine epochs of copper mineralization, ranging in age from late Paleozoic to late Pliocene-Pleistocene, are recognizable in the central Andes of Chile, Peru, Bolivia, and Argentina, and at least four somewhat different epochs characterize the northern Andes of Colombia. Each epoch coincides with a discrete linear sub-belt, some of which extend for more than 2000 km along the length of the orogen. More than 90% of Andean copper resources, mainly as porphyry deposits, are confined to three Cenozoic sub-belts of Paleocene-early Eocene (66-52 Ma), late Eocene-early Oligocene (42-31 Ma), and middle Miocene-early Pliocene (16-5 Ma) ages in southern Peru and Chile. The scarcity of porphyry copper deposits and the increase of pluton-related copper veins in Jurassic and Cretaceous sub-belts farther west in the central Andes is believed to be due to deeper levels of erosion. In the central Andes, copper sub-belts became progressively younger eastward in response to the effects of a compressional tectonic regime imposed on the overriding South American plate, following mid-Cretaceous opening of the South Atlantic Ocean basin. A marked eastward breakout of middle Miocene-early Pliocene copper mineralization up to 300 km into western Argentina and Bolivia is attributed to rapid subduction of young buoyant oceanic lithosphere during the Miocene. A contrasting migration pattern of copper sub-belts characterized the northern Andes, where an early Cretaceous to early Eocene trenchward shift is thought to have been caused by accretion of oceanic terranes to the continental edge. The observed distribution of copper sub-belts reflects the tectonic segmentation of the Andes. Three first-order segments are defined by the well-known Huancabamba and Abancay Deflections, at latitudes 5°S and 14°S, respectively. Each first-order segment is characterized by a profoundly different distribution, timing and, in part, style of copper mineralization, and by distinct copper endowments. Anomalous patterns of sub-belts abut both deflections. Several second-order boundaries appear to have caused more subtle changes along individual copper sub-belts. Additional programs of radiometric dating, on both local and regional scales, are required before the migration and segmentation of copper (and associated metallogenic) sub-belts in the Andes are properly defined and understood.

Geology and metallogeny of copper deposits

I Deposits in Mafic and Ultramafic Complexes.- The Physical and Petrologie Setting and Textural and Compositional Characteristics of Sulfides from the South Kawishiwi Intrusion, Duluth Complex, Minnesota, USA.- Application of Stable Isotopic Studies to Problems of Magmatic Sulfide Ore Genesis with Special Reference to the Duluth Complex, Minnesota.- Controls on the Formation of Komatiite-Associated Nickel-Copper Sulfide Deposits.- Depositional Environments of Volcanic Peridotite-Associated Nickel Sulphide Deposits with Special Reference to the Kambalda Dome.- Geochemistry of the Sudbury Igneous Complex: A Model for the Complex and Its Ores.- Sulfide Petrology and Genesis of Copper-Nickel Ore Deposits.- Types and Distinctive Features of Ore-Bearing Formations of Copper-Nickel Deposits.- On the Role of Metamorphism in the Formation of Nickel-Copper Sulfide Deposits in the Kola Peninsula.- The Gabbro-Wehrlite Association in the Eastern Part of the Baltic Shield.- Peridotitic Komatiites and the Origin of Ores (Southeastern Part of the Baltic Shield).- Geologic Setting of Selected Chromium and Nickel Deposits of China.- II Porphyry Deposits.- Recent Advances in Porphyry Base Metal Deposit Research.- The Geochemical Behaviour of Copper and Molybdenum in Ore-Forming Processes.- Batholith-Volcano Coupling in the Metallogeny of Porphyry Copper Deposits.- Space-Time Distribution, Crustal Setting and Cu/Mo Ratios of Central Andean Porphyry Copper Deposits: Metallogenic Implications.- Metallogenic Zoning of Volcano-Plutonic Belts and Porphyry-Copper Mineralization.- Geological and Structural Conditions of Localization of the High-Grade Ores of Porphyry Copper Deposits.- Elements Determining in the Geological-Structural Model of the Erdenetuin-Obo Copper-Molybdenum Ore Field, Mongolia.- Genetic Aspects of the Recsk Mineralized Complex, Hungary.- Ore-Magmatic Systems of Copper-Molybdenum Deposits.- III Deposits of Volcanic-Hydrothermal Association.- Base Metal Deposits in the Iberian Pyrite Belt.- Copper-Pyrite and Pyrite Base Metal Deposits of the Caucasian Region.- The Hidden Mineralogical and Geochemical Zoning and the Ore-Forming Conditions of Copper and Copper- Lead-Zinc Massive Sulfide Deposits.- Zoning of Massive Sulphide Deposits and their Origin.- Physico-Chemical Conditions of Base Metal Sulphide Ore Formation.- On the Genesis of Barite Associated with Volcanogenic Massive Sulfides, Fukazawa Mine, Hokuroku District, Japan.- IV Sediment-Hosted Deposits.- Diagenetic Features at White Pine (Michigan), Redstone (N. W. Territories, Canada) and Kamoto (Zaire). Sequence of Mineralization in Sediment-Hosted Copper Deposits (Part 1).- Diagenetic Sulphide Mineralization Within the Stratiform Copper-Cobalt Deposit of West Kambove (Shaba- Zaire). Sequence of Mineralization in Sediment-Hosted Copper Deposits (Part 2).- Geochemical Aspects of Stratiform and Red-Bed Copper Deposits in the Catskill Formation (Pennsylvania, USA) and Redstone Area (Canada). Sequence of Mineralization in Sediment-Hosted Copper Deposits (Part 3).- Stratabound Copper Deposits in East South-Central Alaska: Their Characteristics and Origin.- Major Element Geochemistry of the Host Rocks in Some Sediment-Hosted Copper Deposits.- Zechstein Copper-Bearing Shales in Poland. Lagoonal Environments and the Sapropel Model of Genesis.- Formation Conditions of Copper Sandstone and Copper-Shale Deposits.- Major Types of Copper-Bearing Zones in the Soviet Union.- Red-Colored Terrigenous Sediments - Specific Copper- Forming Systems.- Cupriferous Sandstones and Shales of the Siberian Platform.- Genetic Types of Copper Mineralization in the Igarka Area, West of the Siberian Platform.- The Diverse Styles of Sediment-Hosted Copper Deposits in Australia.- Mineral Zoning in Sediment-Hosted Copper-Iron Sulfide Deposits - A Quantitative Kinetic Approach.- Results of Recent Exploration for Copper-Silver Deposits in the Kupferschiefer of West Germany.

Andean Metallogeny: New Discoveries, Concepts, and Updates

A variety of metals and deposit types define the metallogeny of the Andes from Colombia through Ecuador, Peru, and Bolivia to Argentina and Chile, although porphyry copper and epithermal gold deposits undoubtedly predominate and will continue to do so. Discoveries over the last 30 yrs or so, predominantly in the central Andes and especially Chile, have been made using routine, field-based geologic and complementary geochemical methods, a situation that is considered unlikely to change radically in the foreseeable future. The only clearcut evolutionary change is the increased number of deposits being discovered beneath pre- and postmineral cover. The predictive capacity of conceptual geology has had minimal impact on the Andean discovery record but is thought to offer much promise for the future. This introductory article selects mineralization styles and relationships as well as some broader metallogenic parameters as simple examples of geologic concepts that may assist exploration. Emphasis is placed on porphyry copper ± molybdenum ± gold and high-, intermediate-, and lowsulfidation epithermal gold ± silver deposits, although reference is also made to several carbonate rock-hosted precious and base metal deposit types and styles as well as subvolcanic tin, volcanogenic massive sulfide, and slate-belt and intrusion-related gold deposits. Particular emphasis is placed on the potential for exceptionally high grade porphyry copper, porphyry gold, epithermal gold, and subvolcanic tin deposits. Deposits resulting from the oxidation, enrichment, and chemical transport of copper and zinc and mechanical transport of gold and silver during supergene weathering are also briefly highlighted. Si bien la metalogenia de los Andes de Colombia, Ecuador, Peru, Bolivia y Chile se encuentra definida por una gama de metales y estilos de mineralizacion, son los depositos tipo porfido de cobre y epitermal de oro los que dominan en el presente y continuaran prevaleciendo en el futuro. Los descubrimientos de los ultimos 30 anos, predominantemente en los Andes centrales y especialmente en Chile, han sido realizados mediante metodos geologicos rutinarios de campo, generalmente complementados satisfactoriamente por metodos geoquimicos. Se estima que esta situacion dificilmente experimentara variaciones radicales en un futuro cercano. El unico cambio destacable en esta historia evolutiva esta dado por el aumento apreciable de descubrimientos de depositos cubiertos, bajo cobertura pre o postmineral. A nivel andino, la capacidad predictiva de la geologia conceptual ha tenido un impacto minimo en el numero total de descubrimientos, aunque se piensa que su uso debiera garantizar buenas perspectivas futuras. El presente articulo

Reply to discussions of “Age of the Zambian Copperbelt” by Hitzman and Broughton and Muchez et al.

We thank Hitzman and Broughton (2017) and Muchez et al. (2017) for their anticipated interest in our paper, which, based on 15 Re-Os ages for molybdenite intimately associated with Cu-bearing sulfide minerals from seven deposits and prospects throughout the Zambian part of the Central African Copperbelt, shows that there was a major Cu mineralization event during the Lufilian collisional orogeny (Sillitoe et al. 2017). These ages supplement and further support 12 Re-Os molybdenite dates reported previously from the Domes region in the northwestern part of the Zambian Copperbelt (Sillitoe et al. 2015). Both Hitzman and Broughton and Muchez et al. assemble evidence in defense of their Central African Copperbelt models, which assign important roles to Cu-bearing sulfide formation during sediment diagenesis, in conformity with the longstanding paradigm for sediment-hosted stratiform Cu deposits worldwide (Brown 1981; Hitzman et al. 2005). Nonetheless, Muchez et al. concede that the arenite-hosted deposits, exemplified by Mufulira, as well as the ubiquitous vein-hosted sulfide mineralization throughout the Zambian Copperbelt are Lufilian in age but insist that there was also an earlier syndiagenetic Cu introduction event to generate the weakly or non-metamorphosed shale-hosted deposits. In contrast, Hitzman and Broughton reiterate their previous opinion (Selley et al. 2005; Hitzman et al. 2012) that molybdenite was formed exclusively during a late-stage veining event, as reemphasized by their facetious re-titling of our paper. Both discussions cite selected geological features, sulfide textures, and geochronological results to support syndiagenetic Cu introduction. Many of the points raised were already discussed by Sillitoe et al. (2017) and it would be redundant to repeat the same arguments here. Nonetheless, it is worth reemphasizing several key points as well as

Acceptance of the R. A. F. Penrose Gold Medal for 2015

Mr. President, ladies, and gentlemen: My sincere thanks, Jeff, for your career review and accompanying kind words today. A surprising number of previous Penrose medalists have said that they felt humbled by the honor but, in my case, thrilled would perhaps better describe my initial reaction to receiving the news from SEG President Francois Robert. Once the news had fully sunk in, however, I realized that this was a well-deserved award for field geologists worldwide as much as for me as an individual. On occasions such as this, it is customary to thank the teachers, mentors, and colleagues who have greatly influenced one’s geological development. In my case, this is extremely difficult because they number in the thousands: the company geologists with whom I’ve had the good fortune to spend field time throughout the world. They unselfishly shared their observations and data with me and, generally subconsciously, contributed to my ore-deposits understanding over the past 40-odd years. It would be unfair, though, not to mention just a few of the standouts in this long list, with whom field time morphed into mutually shared research interests, eventual joint publication of results, and long-standing friendships: Max Baker, the late Hal Bonham, Dave Burrows, Craig Feebrey, David Hall, Jeff Hedenquist, Rich Lorson, Pepe Perello, the …