Abstract Porphyry Cu deposits in China contain a total resource of ~47 million tonnes (Mt) Cu at average grades ranging mostly from 0.2 to 0.7% Cu (most <0.5% Cu), accounting for 42% of China’s Cu reserves. In terms of contained Cu, 14 Cu-rich porphyry deposits are classified as giant (≥2.0 Mt Cu), and 38 are classified as intermediate (≥0.06 Mt Cu). These giant and intermediate deposits are mainly concentrated in seven belts or districts: Gangdese belt, southern Tibet; Yulong and Zhongdian belts, eastern Tibet; Duolong district, central Tibet; Dexing district and Middle-Lower Yangtze River Valley belt, eastern China; and the Central Asian orogenic belt in northern China. Other isolated giant deposits (e.g., Tongkuangyu) occur in the North China craton. These deposits were formed during Paleoproterozoic (~2100 Ma), Ordovician (~480–440 Ma), Carboniferous (~330–310 Ma), Late Triassic to Early Cretaceous (~215–105 Ma), and Eocene to Miocene (~40–14 Ma), with the majority forming during the latter two time periods. Adakite-like (e.g., high Sr/Y ratio) magmas are most favorable for the formation of the porphyry Cu deposits in China, although some deposits in the Central Asian orogenic belt and the Duolong district are associated with normal calc-alkaline intrusions with low Sr/Y ratios. Approximately 50% of the giant and ~35% of the intermediate porphyry Cu deposits in China formed in arc settings. The Xiongcun, Pulang, Duobuza, Bolong, and Naruo deposits in Tibet formed in continental arc settings, and the Central Asian porphyry Cu belt deposits (e.g., Tuwu-Yandong, Duobaoshan, Wushan, Baogutu, and Bainaimiao) formed in island-arc settings. Ore-forming porphyry magmas in arc settings in China probably formed by partial melting of metasomatized mantle wedge. Ascent and emplacement of porphyry magmas in arc settings was controlled by transpressional (e.g., strike-slip fault systems) or compressional deformation (e.g., arc-parallel thrust fault systems). Approximately 40% of the giant and ~65% of the intermediate porphyry Cu deposits in China occur in postcollisional settings. These deposits are mainly concentrated in the Tibetan Plateau, including four giant (e.g., Qulong, Jiama, Zhunuo, and Yulong) and more than 15 intermediate-size deposits. The mineralized intrusions in postcollisional settings were generated by partial melting of subduction-modified mafic lower crust. Ore-forming metals and sulfur were derived from remelting of sulfide phases that were introduced during precollisional arc magmatism, and the water in the Cu-forming porphyry magmas was concentrated during dehydration reactions in the upper parts of the subducting continental plate and/or degassing of mantle-derived H 2 O-rich ultrapotassic and/or alkaline mafic magmas. Porphyry magma ascent and emplacement were controlled by regional shear zones (e.g., strike-slip fault systems) or extensional fracture arrays (e.g., normal fault systems) in postcollisional settings. Porphyry Cu deposits in China mostly show typical alteration zoning from inner potassic to outer propylitic zones, with variable phyllic and argillic overprints. Potassic alteration can be generally subdivided into inner K-feldspar and outer biotite zones, with K-feldspar–rich alteration mostly earlier than biotite-rich alteration. Phyllic alteration generally comprises early-stage chlorite-sericite and late-stage quartz-sericite alteration, and the chlorite-sericite zone typically occurs beneath the quartz-sericite zone. Lithocaps are absent in most of the porphyry Cu deposits in China, even for those in the youngest (~30–14 Ma) ores in the Gangdese belt. Alteration architecture of the porphyry Cu deposits in China is mainly dependent on the structural setting and degree of telescoping. Telescoping of alteration assemblages in the postcollisional porphyry Cu deposits is more strongly developed than that in island and continental arc porphyry Cu deposits. This is probably because postcollisional porphyry Cu deposits and districts in China either experienced higher rates of synmineralization uplift or suffered more complex structural superposition, compared with those formed in magmatic arcs. Hypogene Cu mineralization in some giant porphyry deposits in China (e.g., Xiongcun, Qulong) is associated with potassic alteration and particularly with late-stage biotite alteration. But hypogene mineralization for more than 50% of giant porphyry Cu deposits, including the Dexing, Yulong, Tuwu-Yandong, Duobaoshan, and Tongkuangyu deposits, is characterized by a Cu sulfide assemblage with phyllic alteration, particularly with chlorite-sericite alteration. The presence of several world-class postcollisional porphyry Cu provinces in China demonstrates that the generation of porphyry Cu deposits does not always require a direct link to oceanic plate subduction.

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 The Yidun arc, part of the Sanjiang Paleo-Tethyan orogenic belt in eastern Tibet, hosts several porphyry Cu deposits in its southern section, whereas abundant contemporaneous but barren granitoid intrusions occur in the northern section. Here we present an integrated, temporally constrained dataset of zircon and apatite compositions together with whole-rock geochemical results for both the fertile and barren suites in the Yidun arc. We investigate the probable factors leading to such contrasting porphyry Cu fertilities and also assess the application of geochemical and mineral proxies for porphyry Cu exploration. Both the fertile and barren suites in the Yidun arc share similar petrographic and geochemical characteristics typical of arc magmas. However, the two suites have distinct differences in certain trace elements and element ratios (e.g., Sr, Y, Sr/Y, V/Sc, Eu anomaly). The fertile suites have adakite-like character, with high Sr/Y, La/Yb, and V/Sc ratios, and show no or minimal negative Eu anomalies, indicating early dominant amphibole with limited plagioclase fractionation. By contrast, the barren suites have low Sr/Y, La/Yb, and V/Sc ratios, and display minimal to significant negative Eu anomalies. These barren suites probably formed by crystal fractionation dominated by plagioclase, with limited amphibole crystallizing from the same parental magma. Zircon geochemical data for both suites combined with Rayleigh fractionation modeling show that zircon compositions (e.g., Hf, Ti, [Yb/Dy] N , Eu/Eu*, Ce/Nd) are affected by the compositions, water content, and redox state of the parental magma, as well as by prior or concurrent crystallization of minerals (e.g., plagioclase, amphibole, apatite, titanite). For the fertile suites, the high zircon Eu/Eu* (0.43–0.91), Δ FMQ (0.8–2.4; where Δ FMQ is the log f O 2 difference between the sample value and the fayalite-magnetite-quartz mineral buffer), the presence of the assemblage amphibole + titanite + quartz + magnetite, and high whole-rock Fe 2 O 3 /FeO, Sr/Y and V/Sc ratios, collectively indicate that associated magmas were hydrous and oxidized. For the barren suites, the common presence of the assemblage amphibole + ilmenite, low zircon Eu/Eu* (0.01–0.34) and Δ FMQ (–3.3 to +0.5), and low whole-rock Fe 2 O 3 /FeO, Sr/Y, and V/Sc ratios, together indicate that the related magmas were hydrous but reduced. Magmatic apatites in the fertile suites have higher SO 3 contents (0.07–0.79 wt %) than those in the barren suites (<0.04 wt % SO 3 ). The estimated magmatic sulfur contents for the fertile suites are 35 to 160 ppm, whereas for the barren suites, their related magmas were sulfate poor. Compared to the hydrous, oxidized, and S-rich fertile suites in the southern Yidun arc, the reduced and sulfate-poor characteristics of the barren suites hinder the transport of adequate S and metals to form porphyry Cu deposits, even though they are hydrous; thus there is little potential for porphyry Cu deposits in the northern Yidun arc. Whole-rock Sr/Y (>20), V/Sc (>32.5–0.385 × wt % SiO 2 ), Eu/Eu* (~1) and 10,000*(Eu/Eu*)/Y (>400) ratios, zircon Eu/Eu* (>0.4) and Δ FMQ (>1), and apatite SO 3 contents (>0.1 wt %) can help to discriminate porphyry Cu intrusions from barren granitoids in the Yidun arc, indicating their usefulness as porphyry Cu fertility indicators. The zircon Ce anomaly (Ce 4+ /Ce 3+ , Ce/Ce*, Ce/Nd), however, overlaps between the oxidized fertile and reduced barren suites, hampering its use to estimate relative magmatic redox state and as a robust porphyry Cu fertility indicator. The combination of whole-rock analyses and zircon and apatite compositions helps focus porphyry Cu exploration on prospective areas, coupled with investigations of structural geology, geophysical surveys, and mapping of hydrothermal alteration.