TECTONICS AND GOLD METALLOGY
The distribution of gold-rich porphyry and epithermal deposits is skewed towards the late Cenozoic. The ores are associated with subvolcanic plutonic complexes and shallower parts of oceanic and continental arcs in the convergent margins of the circum-Pacific and Tethyan of southern Europe. Most deposits that formed in the upper few km of crust before ca. 20-30 Ma, were uplifted and eroded, and thus lost from the geologic record, although significant exceptions date back through all Phanerozoic orogens, and even to the Archean. Carlin-type deposits are only widely recognized in Nevada (Tertiary) and perhaps along the SW edge of the Yangtze craton (Jurassic), so knowledge about these remains too limited to relate the ores to major global tectonic patterns.
Orogenic gold deposit formed in medium-grade metamorphic belts tens of millions of years subsequent to host rock deposition. The deposits in both eastern China and Sonora are hosted in high-grade rocks and provide global anomalies where deposits post-date host rock metamorphism by billions of years, leading to revisions in the ore genesis model. Preserved orogenic gold deposits correlate in time with addition of new oceanic lithosphere to craton margins during supercontinent growth at ca. 2.8-2.55 Ga, 2.1-1.75 Ga, and 650-35 Ma. Major lithospheric instabilities controlling ore formation include thickening by terrane accretion, subduction of a spreading ridge, rollback or delamination of subducted oceanic lithosphere, or Precambrian plume events
The IOCG deposits represent the one group of gold ores in intracratonic settings, typically 100-200 km inland from the craton margins, where extension and anorogenic magmatism occur between areas of Archean and Proterozoic SCLM. The partial melting of metasomatized SCML, either by mantle underplating or plume episodes, leads to IOCG development in buoyant and refractory Precambrian cratons, such that even shallowly formed deposits have been preserved.