MINERAL DEPOSITS AND THEIR GENESIS 493 Figure Pacific Rim gold copper mineralization models This cross section sketch is an example of the types of mineralization associated with felsic intrusive rocks Reproduced with permission from the Society of Economic Geologists Inc., Southwest Pacific Rim Gold Copper Systems: Structures, Alteration, and Mineralization, p 6, Fig 1.1, Corbett GJ and Leach TT (1998) example is at Lihir island within the Pacific ‘ring of fire’, where large-scale mining recently commenced on very fine-grained gold in pyritic mineralization within an inactive volcanic caldera The Carlin-type deposits of Nevada, on the other hand, are situated along regional structural trends The gold mineralization is commonly so finely disseminated within the dark impure calcareous host rocks that mining limits are determinable only by assay, and the discovery in the 1970s was hailed as ‘virus gold’ Rhyolites and dacites, the extrusive forms of granites and granodiorites, are host rocks to economically and geologically important types of base-metal sulphide mineralization that are transitional between sub-surface and surface The Iberian pyrite belt of southern Spain and Portugal, and the Kuroko deposits of Japan are leading examples Subsurface mineralization of transgressive stockworks in explosive rhyolite domes underlies massive stratiform sulphide bodies that are interpreted as deposited at surface in a submarine environment (Figure 8) These two closely associated deposits, of distinctly different style and appearance, are attributed to the same mineralizing ore fluids at work in the subsurface and, after exhalation, above the rock-water interface Figure Schematic section through an idealized volcanic associated massive sulphide deposit showing the underlying feeder stockwork and typical mineralogy Py pyrite, sp ỵ spha sphalerite, ga galena, cp chalcopyrite Reproduced from Evans AM (ed.) (1995) Introduction to Mineral Exploration Oxford: Blackwell Science Associations with Ancient Sedimentary Rocks Knowledge of present-day surface processes assists in the understanding of ancient sedimentary deposits such as coal, and salt deposits formed by evaporation of brines from closed basins or sabkhas Geological details vary, but the genetic picture is clear enough to guide exploration for further resources However,