Abstract China produces about 450 t Au per year and has government stated in-ground reserves of approximately 12,000 t Au. Orogenic gold, or gold deposits in metamorphic rocks, and associated placer deposits compose about 65 to 75% of this endowment, with lodes existing as structurally hosted vein and/or disseminated orebodies. The abundance of orogenic gold deposits reflects Paleozoic to Triassic closure of Paleo-Tethyan ocean basins between Precambrian blocks derived from Rodinia and Gondwana as well as late Mesozoic-Cenozoic circum-Pacific events and Cenozoic Himalayan orogeny. The deposits range in age from middle Paleozoic to Pleistocene. The Jiaodong Peninsula contains about one-third of China’s overall endowment, and large resources also characterize East Qinling, West Qinling, and the Youjiang basin. Although gold ores in Jiaodong postdate formation and metamorphism of Precambrian host rocks by billions of years, they are nevertheless classified here as orogenic gold ores rather than as a unique Jiaodong-type or decratonic-type of gold deposit. Similarly, although many workers classify the gold lodes in the Youjiang basin and much of West Qinling as Carlin-type gold, they show significant differences from gold ores in Nevada, United States, and are better defined as epizonal orogenic gold deposits. Although there are widespread exposures of Precambrian rocks in China, there are no significant Precambrian gold deposits. If large ancient orogenic gold deposits formed in Archean and Paleoproterozoic rocks, then they have been eroded, because these deep crustal rocks that are now exposed in China’s cratonic blocks have been uplifted from levels too deep for orogenic gold formation. The oldest large gold deposits in China are perhaps those of the Qilian Shan that were formed in association with Silurian tectonism along the present-day southwestern margin of the North China block. Closure of ocean basins in the outer parts of the Central Asian orogenic belt led to late Carboniferous to Middle Triassic orogenic gold formation in the Tian Shan, Altay Shan, Beishan, and northwestern North China block. Deformation associated with amalgamation of the North China block, northern Tibet terranes, South China block, and Indochina, as well as initial Paleo-Pacific subduction, can be related to Late Triassic orogenic gold formation in West Qinling, East Kunlun, Youjiang basin, West Jiangnan (Xuefengshan belt), Hainan Island, and Yunkaidashan gold provinces. In the middle Mesozoic, continued subduction along the Paleo-Pacific margin was associated with gold ores forming in East and Central Jiangnan, whereas early to middle Mesozoic deformation along the northern North China block formed important orogenic lodes in Precambrian basement (e.g., Jiapigou, Zhangjiakou, and Yanshan districts). Continued Yanshanian orogeny in the eastern half of the North China block led to extensive orogenic gold formation during the main period of decratonization and regional extension at ca. 135 to 120 Ma (e.g., Jiaodong, Liaodong, Chifeng-Chaoyang, Zhangbaling, Taihangshan, and East Qinling). At the same time, strike-slip events in central Transbaikal were associated with orogenic gold formation in both Russia and adjacent northeastern China and likely are the source for China’s most productive gold placers in the upper Heilongjiang basin. China’s youngest orogenic gold deposits formed in the Ailaoshan, Lanping basin, Ganzi-Litang belt, Daduhe district, and areas south of the Lhasa terrane in Tibet during the middle Cenozoic, as well as in the northern half of the Central Range of Taiwan during the Pliocene-Pleistocene.

Abstract Oligocene to Miocene postcollisional porphyry Cu deposits in the Gangdese belt in southern Tibet contain total resources of >20 million metric tons (Mt) Cu and are genetically associated with granodioritic-quartz monzogranitic porphyry intrusions with adakite-like signatures (e.g., Sr/Y >40). The adakite-like magmatic rocks in the southern sub-belt of the eastern Gangdese belt (east of 87° E) range in age from ca. 38 to 18 Ma, whereas those in the northern sub-belt range in age from ca. 21 to 10 Ma. Mineralization ages of the porphyry Cu deposits in the eastern Gangdese belt also show a decreasing trend from south to north, with the deposits in the southern sub-belt being ca. 30 Ma and the deposits in the northern sub-belt, 21 to 13 Ma. Many more of the adakite-like intrusions in the northern part are associated with porphyry copper deposits, compared with those in the southern part. The adakite-like intrusions exhibit high SiO 2 (>60 wt %), Al 2 O 3 (mostly >15 wt %), K 2 O (>2 wt %), and Sr (>300 ppm); low Y (<15 ppm); enrichment in large ion lithophile elements (LILE); and depletion in high field strength elements (HFSE). These data are consistent with partial melting of a subduction-modified lower crust. However, the extremely variable Sr-Nd isotope compositions (initial 87 Sr/ 86 Sr = 0.7037-0.7120; £ N d( t ) = +5.7 to -10.6) of the intrusions require incorporation of lower crust with an end member having extremely enriched Sr-Nd isotope compositions, and the anhydrous character of the eclogitized lower crust in turn requires melting via addition of exogenous H2O and/or heat. These features, together with the northward younging of adakite-like magmatism and associated porphyry Cu mineralization in the eastern Gangdese belt, indicate that the intrusions and mineralization could have been caused by H2O-added melting of the lower crust. Such melting would have been triggered by the late Eocene to Miocene northward relatively hot (~15°C/km geotherm) subduction of the Indian continental plate. Under hot subduction conditions, the main hydrous minerals (e.g., phengite, epidote, chlorite, biotite) in the upper crust of the Indian continental plate would have lost most of their mineralogically bound water before reaching a depth of 100 km. This devolatilization would have resulted in progressive fluid-fluxed melting of the metasomatized wedge of subcontinental lithospheric mantle and part of the lower crust; the former produced ultrapotassic-like and/or alkaline mafic magmas. Underplating of such mafic magma, rising from their source area (>80 km) into the lower part (~60-70 km) of the lower crust, together with direct input of fluid liberated from the subducting Indian continental plate, resulted in H2O-added melting of the Tibetan lower crust, generating H2O-rich adakite-like magmas in the eastern Gangdese belt. The adakite-like rocks in the western Gangdese have very similar geochemical compositions to those in the eastern Gangdese, and their generation can also be explained by the melting of subduction-modified mafic lower crust with input of ultrapotassic melt. However, in contrast, colder (5°-8°C/km geotherm) subduction of the Indian continental plate and the opposite younging trend from north to south for the postcollisional adakite-like and ultrapotassic rocks in the western Gangdese belt suggests that the generation of the adakite-like rocks in the west was triggered by a different geodynamic process, which is most likely roll-back and gradual break-off of the northward subducting Indian slab from north to south. We suggest that H2O in the postcollisional ore-related magmas originated from dehydration reactions in the upper parts of the subducting continental plate. Thermal structure of the continental subduction zone and the amount of continental crust subducted to depth seem to be two critical controls on the generation of porphyry Cu deposits in the Tibetan postcollisional setting.

Abstract There are six distinct classes of gold deposits, each represented by metallogenic provinces having hundreds to more than 1,000 tonnes (t) gold production. These deposit classes are as follows: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver deposits; (4) copper-gold porphyry deposits; (5) iron oxide copper-gold deposits; and (6) gold-rich volcanic-hosted massive sulfide to sedimentary-exhalative (sedex) deposits. This classification is based on ore and alteration mineral assemblages, ore and alteration metal budgets, ore fluid pressure(s) and compositions, crustal depth or depth ranges of formation, relationship to structures and/or magmatic intrusions at a variety of scales, and relationship to the P-T-t evolution of the host terrane. The classes reflect distinct geodynamic settings. Orogenic gold deposits are generated at midcrustal (4–16 km) levels proximal to terrane boundaries, in transpressional subduction-accretion complexes of cordilleran-style orogenic belts; other orogenic gold provinces form inboard by delamination of mantle lithosphere or by plume impingement. Carlin and Carlin-like gold deposits develop at shallow crustal levels (<4 km) in extensional convergent margin continental arcs or back arcs; some provinces may involve asthenosphere plume impingement on the base of the lithosphere. Epithermal gold and copper-gold porphyry deposits are sited at shallow crustal levels in continental margin or intraoceanic arcs. Iron oxide copper-gold deposits form at middle to shallow crustal levels; they are associated with extensional intracratonic anorogenic magmatism. Proterozoic examples are sited at the transition from thick refractory Archean mantle lithosphere to thinner Proterozoic mantle lithosphere. Gold-rich volcanic-hosted massive sulfide deposits are hydrothermal accumulations on or near the sea floor in continental or intraoceanic back arcs. The compressional tectonics of orogenic gold deposits are generated by terrane accretion; high heat flow stems from crustal thickening, delamination of overthickened mantle lithosphere inducing advection of hot asthenosphere, or asthenosphere plume impingement. Ore fluids advect at lithostatic pressures. The extensional settings of Carlin, epithermal, and copper-gold porphyry deposits result from slab rollback driven by negative buoyancy of the subducting plate, and associated induced convection in asthenosphere below the overriding lithospheric plate. Extension thins the lithosphere, advecting asthenosphere heat; promotes advection of mantle lithosphere and crustal magmas to shallow crustal levels; and enhances hydraulic conductivity. Siting of some copper-gold porphyry deposits is controlled by arc-parallel or orthogonal structures that in turn reflect deflections or windows in the slab. Ore fluids in Carlin and epithermal deposits were at near-hydrostatic pressures, with unconstrained magmatic fluid input, whereas ore fluids generating porphyry copper-gold deposits were initially magmatic and lithostatic, evolving to hydrostatic pressures. Fertilization of previously depleted subarc mantle lithosphere by fluids or melts from the subducting plate, or incompatible element-enriched asthenosphere plumes, is likely a factor in generation of these gold deposits. Iron oxide copper-gold deposits involve prior fertilization of Archean mantle lithosphere by incompatible element enriched asthenospheric plume liquids, and subsequent intracontinental anorogenic magmatism driven by decompressional extension from far-field plate forces. Halogen-rich mantle lithosphere and crustal magmas form, and likely are the causative intrusions for the deposits, with a deep crustal proximal to shallow crustal distal association. Gold-rich volcanic-hosted massive sulfide deposits develop in extensional geodynamic settings, where thinned lithosphere extension drives high heat flow and enhanced hydraulic conductivity, as for epithermal deposits. Ore fluids induced hydrostatic convection of modified seawater, with unconstrained magmatic input. Some gold-rich volcanic-hosted massive sulfide deposits with an epithermal metal budget may be submarine counterparts of terrestrial epithermal gold deposits. Real-time analogues for all of these gold deposit classes are known in the geodynamic settings described, excepting iron oxide copper-gold deposits.