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Abstract:The Tongling area is one of the 7 ore‐cluster areas in the Middle‐Lower Yangtze metallogenic belt, East China, and has tectonically undergone a long‐term geologic history from the late Paleozoic continental rifting, through the Middle Triassic continent‐continent collision to the Jurassic‐Cretaceous intracontinental tectono‐magmatic activation. The Carboniferous sedimentary‐exhalative processes in the area produced widespread massive sulfides with ages of 303–321 Ma, which partly formed massive pyrite‐Cu deposits, but mostly provided significant sulfur and metals to the skarn Cu mineralization associated with the Yanshanian felsic intrusions.

The Yulong ore body is the largest Cu deposit (6.22 million metric tons [Mt] at 0.99% Cu) in the 300 km long Himalayan porphyry copper belt, and is controlled by major Cenozoic strike-slip faults in the eastern Indo-Asian collision zone. It is associated with a steeply dipping, pipe-like multiphase (42-35 Ma) monzogranitic stock. The host rocks are potassic calc-alkaline or shoshonitic, and show geochemical affinities with adakites. They appear to have been derived from a thickened lower crustal source in East Tibet.The Yulong deposit consists of a ring-shaped, high-grade Cu-Au zone overlying and/or surrounding a porphyry-type Cu-Mo ore body. Cu-Mo mineralization produced a steeply dipping, pipe-like, veinlet-disseminated ore body within the stock. Associated hydrothermal alteration produced K-silicate and quartz-sericite assemblages within the stock, and contemporaneous propylitic alteration in the Upper Triassic sandy-slate wall rock. Fluid inclusion and δ18O-δD data indicate that the ore-forming fluid was supercritical, and exsolved from a high-level magma chamber at 620°C; it then separated into a hypersaline aqueous liquid and a coexisting low-salinity vapor at 340°-600°C.The high-grade Cu-Au zone (3 Mt at 4.74% Cu, and 4.5 g/t Au) is dominated by a supergene chalcocite-malachite blanket resting on an underlying supergene/hypogene sulfide transition unit and a hypogene pyrite-chalcopyrite sulfide unit. The Cu-Au zone was controlled by a subhorizontal or gently outward dipping breccia horizon developed along the marginal fracture zone near the roof of the stock, produced by hydrothermal brecciation due to regional uplift and/or fluid boiling. Alteration associated with the hypogene Cu-Au mineralization was texture-destructive advanced argillic alteration, characterized by associations of quartz, kaolinite, dickite, endellite, montmorillonite, hydromica, and minor alunite. It mainly developed within the breccia horizons, and partially over-printed the early-formed K-silicate zone and the quartz-sericite zone. Associated mineralization was of the high-sulfidation epithermal-type, characterized by chalcocite, tennantite, covellite, bornite, and minor pyrite, which formed the main ore body in the high-grade Cu-Au zone. Epithermal fluids also caused the dissolution of early-formed sulfides and remobilization of Cu-Mo, the latter transported into the intense advanced argillic alteration halo within the mineralized stock. This late-stage alteration and mineralization is attributed to a CO2-rich, low-temperature (<350°C), low-salinity (<12 wt% NaCl equiv.) meteoric fluid, involving input of magmatic fluid.Based on alteration, mineralization, fluid inclusion and stable isotopic data, a two-stage genetic history has been reconstructed for the Yulong deposit. It spans (1) a magmatic hydrothermal environment reflecting the emplacement of the monzogranite stock and Cu-Mo introduction through (2) hydrothermal fluid infiltration of breccia zones to epithermal overprinting.

In order to document the chemical characteristics of sources of a continental flood basalt (CFB) and to understand its origin, we studied four typical picrite-basalt flows and three picritic intrusions in the Emeishan picrite-cluster field (5 x 104 km2 area), located in the southwestern part of the Emei large igneous province. Major and trace elements, and Sr-Nd-Pb isotopic compositions, are reported for picrites and associated basalts in the picrite-cluster field, regarded as the axial area of the Emei mantle plume. These rocks exhibit a range of MgO contents (4.2-27.2%), variable degrees of LREE enrichment (LaN/YbN = 2.7-29.0), and heterogeneous isotopic ratios (εNd(t) = 4.84 to -4.00; initial 87Sr/86Sr = 0.7023-0.7064; 206Pb/204Pb = 18.034-20.641). Nd, Sr, and Pb isotopic covariations are similar to at least three groups of the picrites and basalts. Ontong Java-like lavas yielded low (87Sr/86Sr)i (<0.7045), high ε Nd(t) (>2.5), and the lowest (Ce/Yb)N (∼4), La/Sm (∼3), Th/Nb (∼0.75), La/Nb (∼0.85), and Ba/Nb (∼8) ratios, suggesting a focus zone (FOZO)-like mantle source. Cook-Austral-like lavas have high 206Pb/204Pb (19.0), low (87Sr/86Sr)i (<0.7045), and high Sm/Yb (>4), Nb/Y (>1) and Zr/Y (>8), similar to the HIMU component. Heard-like lavas yielded high (87Sr/86Sr)i (0.7044 ∼ 0.7060), low εNd(t) (1.7 to -3.0), 206Pb/204Pb (18.75-18.03) and 208Pb/204Pb (37.8-39.0), and high (Ce/Yb)N (>10), Ba/Nb (>30), and Th/Nb (>0.1), which might be explained by mixing of picritic magmas from the plume with lamproitic melt from continental lithospheric mantle. Three samples outside the three groups have Sr-Nd isotopic signatures similar to EM I, and high Th/Nb (>0.2), La/Nb (>1.5), and low Nb/U (<25), suggesting a pelagic sediment source component. The picritic intrusives have low εNd(t) (0.32-0.59), intermediate (87Sr/86Sr)i (0.7037-0.7042), very high Th/Nb (0.11-0.20), and low Nb/U (<25), implying minor crustal assimilation. The trace elements and Sr-Nd-Pb isotope geochemistry of the Emei picrites and associated basalts reflect processes involving: (1) partial melting of a heterogeneous, eclogite-bearing source to produce picritic magmas; then (2) mixing with small amounts of melt from the continental lithospheric mantle; and (3) crustal assimilation during picritic magma ascent. The heterogeneity of this source is related to recycling of subducted oceanic crust and associated sediments into the deep upper mantle.

Abstract A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province (LIP), SW China was investigated for laser microprobe 40Ar/39Ar dating. There are two 40Ar/39Ar age groups for these basalts, corresponding to 259–246 Ma and 177–137 Ma, respectively. A well‐defined isochron gives an eruption age of huge quantities of mafic magmas at 258.9±3.4 Ma, which is identical to previous dating and paleontological data. Much younger 40Ar/39Ar ages for some basalts with low‐greenschist metamorphic facies probably recorded a late thermo‐tectonic event caused by collision between the Yangtze and Qiangtang continental blocks during the Mesozoic, which resulted in the reset of argon isotope system. The 40Ar/39Ar age data, we present here, combined with previous dating and paleontological data, suggest relatively short duration (about 3 Ma) of mafic volcanism, which have important implication on mantle plume genesis of the Emeishan continental flood basalts in the LIP.

The Okinawa trough is an active, backarc-spreading basin in which hydrothermal fluids are venting from black and white smoker chimneys along a felsic volcanic ridge. The Okinawa seafloor hydrothermal precipitates are comparable to Kuroko-type massive sulfide deposits in many respects. Both systems occur in backarc settings and are hosted by a suite of bimodal volcanic rocks. They show mound-like features and contain predominantly Zn-Pb-Cu metal associations. Aqueous and CO2-rich hydrothermal fluids from the JADE field exhibit high trapping temperatures (up to 420°C), and moderate salinities (up to 8% NaCl equiv.). We provide evidence for the contribution of volatiles from a magmatic source to the actively forming submarine hydrothermal system. The following features in the JADE field support a magmatic component within this system: (1) the presence of a shallow-level felsic magma chamber 1-2 km beneath the seafloor; (2) anomalously high heat flow within the hydrothermal field; (3) a high content of CO2 and CH4 in the hydrothermal plume; (4) effervescence of volatile species (e.g., CO2, CH4, H2, N2,) in the hydrothermal fluid that forms independent discharges as CO2-rich fluid through CO2 hydrate pipes near black smoker chimneys; (5) helium isotope data demonstrating that these gases were derived from a mantle source; (6) high-temperatures and moderate to high fluid-inclusion salinities; (7) oxygen isotopic compositions of altered rocks and quartz indicating that mineralizing fluids have a δ18O composition consistent with a mixture of magmatic fluid and seawater.

Abstract Numerical simulation of fluid migration during the ore‐forming process of the Carboniferous exhalation‐sedimentary (Sedex) massive sulfide deposits in the Tongling district shows that fluid and thermal activities in lying‐wall rocks were limited to a small area around the main draining passage, which led to weak mineralization and alteration in the lying‐wall rock. Temperature and fluid fields indicate that mineralization and alteration in the lying‐wall rock of the Sedex‐type deposits are usually weaker than those of volcano‐hosted massive sulfide deposits. Fluid migration involves the following processes: seawater penetrating and leaching the lying‐wall rocks, then mixing with ascending hydrothermal fluids in the main draining passage, and finally jetting into seafloor. Although fluid activity‐influenced area is rather small, the content of metals leached out from the lying‐wall rocks is high enough to form large‐scale ore deposits. Tensional contemporaneous faults accompanied with strong heat flows controlled the formation and distribution of Sedex deposits. The tensional tectonic regime on the northern margin of the Yangtze block during the Hercynian provided Sedex deposits with a prerequisite geodynamic condition.

Abstract The Pulang porphyry copper deposit is located in the Zhongdian island are belt, NW Yunnan, in the central part of the Sanjiang area, SW China, belonging to the southern segment of the Yidun island arc belt on the western margin of the Yangtze Platform. In the Yidun island arc, there occur well‐known “Gacun‐style” massive sulfide deposits in the northern segment and plenty of porphyry copper deposits in the southern segment, of which the Pulang porphyry copper deposit is one of the representatives. Like the Yulong porphyry copper deposit, this porphyry copper deposit is also one of the most important porphyry copper deposits in the eastern Qinghai‐Tibet Plateau. But it is different from other porphyry copper deposits in the eastern Qinghai‐Tibet Plateau (e.g. those in the Gangdise porphyry copper belt and Yulong porphyry copper belt) in that it formed in the Indosinian period, while others in the Himalayan period. Because of its particularity among the porphyry copper deposits of China, this porphyry copper deposit is of great significance for the study of the basic geology and the evaluation and prediction of mineral resources in the Zhongdian island arc belt. However, no accurate chronological data are available for determining the timing of mineralization of the porphyry copper deposit. By field observation in the study area and Re‐Os dating of molybdenite and K‐Ar dating of hydrothermal minerals and whole rock from the typical geological bodies, the timing of mineralization of the porphyry copper deposit has systematically been determined for the first time. The K‐Ar age for the hydrothermal mineralization of biotite‐quartz monzonitic porphyry that has undergone patassic silicate (biotite and K‐feldspar) alteration ranges from 235.4±2.4 to 221.5±2.0 Ma and the Re‐Os age for molybdenite in the quartz‐molybdenite stage is ∼213±3.8 Ma. These data are very close to each other, suggesting that the ore‐forming processes of the Pulang porphyry copper deposit was completed in the Indosinian. But the K‐feldspar K‐Ar age of the main orebodies suggests that the hydrothermal activity related to porphyry copper mineralization continued till ∼182.5±1.8 Ma. This indicates that the lifespan of the hydrotthermal system related to porphyry copper mineralization may have lasted at least 40 Ma. This hydrothermal thermal system with such a long lifespan may be one of the necessary conditions for forming large porphyry copper deposits with a high grade. No late Yanshanian and/or Himalayan magmatism (mineralization) were superimposed in the Pulang porphyry copper deposit.

AbstractThe middle‐lower Yangtze area underwent a series of complex tectonic evolution, such as Hercynian extensional rifting, Indosinian foreland basining, and Yanshanian transpression‐transtension, resulting in a large distinctive Cu‐Fe‐Au metallogenic belt. In the tectonic evolution, large‐scale migration and convergence of fluids toward foreland basins induced during the collisional orogeny of the Yangtze and North China continental blocks were of vital importance for the formation of the metallogenic belt. Through geological surveys of the middle‐lower Yangtze area, three lines of evidence of large‐scale fluid migration are proposed: (1) The extensive dolomitic and silicic alteration penetrating Cambrian‐Triassic strata generally occurs in a region sandwiched between the metallogenic belt along the Yangtze River and the Dabie orogenic belt, and in the alteration domain alternately strong and weak alteration zones extend in a NW direction and are controlled by the fault system of the Dabie orogenic belt; it might record the locus of the activities of long‐distance migrating fluids. (2) The textures and structures of very thick Middle‐Lower Triassic anhydrock sequences in restricted basins along the river reveal the important contribution of the convergence of regional hot brine in restricted basins and the chemical deposition or their formation. (3) Early‐Middle Triassic syndepositional iron carbonate sequences and Fe‐Cu‐Pb‐Zn massive sulfide deposits alternate with anhydrock sequences or are separated from the latter, but all of them occur in the same stratigraphic horizon and are intimately associated with each other, being the product of syndeposition of high‐salinity hot brine. According to the geological surveys, combined with previous data, the authors propose a conceptual model of fluid migration‐convergence and mineralization during the Dabie collisional orogeny.

AbstractAlmost all intraplate caprocks experienced strong deformation during the convergence of microplates, and then disintegrated into many secondary geologic units with the special characters, such as irregular boundaries and particular structural assemblages. In order to understand the formation mechanism of these special phenomena, a rheological experiment on the structural scenery of the Tongling area is carried out. The result shows that the primary regular and uniform boundaries of the Tongling area becomes irregular because of the enclosing and confinement of surrounding geological units in the process of “compression‐shearing‐rotation‐drag”; simultaneously, two specific “drag depressions” developed at two opposite corners of the block. The former and the later phenomena can be regarded as a typical regional‐scale rheological effect and necessary outcome of intraplate deformation respectively.

Abstract Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen‐family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron‐family and platinum‐family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle‐core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep‐seated ore‐forming material, and thus elements such as gold and silver concentrated in the core and on the core‐mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas‐liquid state to the near‐surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE‐plunging crown of the Fuping mantle‐branch structure, the paper analyzes ductile‐brittle shear zone‐type gold fields (Weijiayu) at the core of the magmatic‐metamorphic complex, principal detachment‐type gold fields (Shangmingyu) and hanging‐wall cover fissure‐vein‐type lead‐zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore‐forming material and constructs an ore‐forming and ‐controlling model.

AbstractThe distribution of Neogene felsic porphyries intruding in earlier granitic batholiths was mainly controlled by north‐south‐tending rifting zones and normal faults. The main rock types of the felsic porphyries include granodiorite‐porphyry, monzonitic granite‐porphyry and quartz monzonitic porphyry. The porphyries are characterized by high SiO2(≥64.26%) and Al2O3(>15% at 70% SiO2), low Y and HREE (Yb) contents, strong enrichment of LILE and LERR, especially K and Sr. Geochemical features of the porphyries show distinct adakitic magma affinity. Nd, Sr and Pb isotopic compositions of the porphyries form a linear alignment from MORB to EM2, suggesting a mixing of the MORB reservoir with the metasomatized mantle reservoir. Considering also the geochemical characteristics of the porphyries and the sequence of observable structural‐thermal‐magmatic events at Gangdise, it is thought that the Neogene porphyries were formed by partial melting of dead subducted oceanic crust in a post‐collision setting. K‐enrichment in the porphyries is attributed to the interaction of slab‐derived melts, i.e., adakites, with the metasomatized mantle during the ascent There might be a delamination of residual eclogites or amphibole eclogites before the eruption of potassic lava on the Tibetan plateau since 13 Ma.

Abstract Geochronology of continental flood basalts sampled from the Emei large igneous province (LIP) on the western margin of the Yangtze platform was investigated by the laser microprobe 40Ar/39Ar dating technique. These basalts yield a fairly wide range of 40Ar/39Ar ages, varying from 259 to 135 Ma. One basalt sample, at least altered, recorded the oldest 40Ar/39Ar age of about 259 Ma, corresponding to a peak eruption age of the Emei LIP continental flood basalts. Most of the samples yield much younger ages from 135 to 177 Ma, which are consistent with the K‐Ar ages for the same samples (122.8–172.1 Ma). The dating data suggest that these Permian basalts had been widely affected by the regional tectonothermal event at 177–135 Ma. The event was probably caused by the convergence and collision among the Laurasia, Yangtze and Qiangtang‐Qamdo continental blocks on the eastern margin of the Qinghai‐Tibet plateau after the late Triassic. The age of the event reflects the timing of the peak collisional orogeny.

A preliminary organic geochemical study shows that the sulphide ores from the hydrothermal deposit of the Okinawa Trough are generally low in the total organic carbon and extremely low in the soluble organic matter. In the aliphatic hydrocarbon fraction, the n‐alkanes range from C15to C35, with usual maxima in the middle n‐C20region and strong odd‐carbon number predominance when n> C25(CPI = 1.2). The dominant analog in the aromatic fraction is phenanthrene, a polynuclear aromatic hydrocarbon, which provides evidence for hydrothermal activity. The organic matter derived mainly from marine planktonic and terrigenous vascular plants is entrapped in a high‐temperature regime such as an active chimney and cooled quickly in the sulphide ores on the seafloor. Organic matter and sulphides are definitely products of a high‐temperature alteration. The biomarker compounds indicate that the ores are formed under low Eh and pH conditions—a reducing to anoxic environment, which is favourable for sulphates to be reduced into sulphides by biogenic (bacterial) or abiogenic activity.

Boninitic rocks and associated high‐magnesian basalt and high‐iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island‐Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well‐developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low‐Ca pyroxenes and by low CaO/Al2O3ratios (<0.67) and high Cr (>1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low‐Ca modern boninites and SHMB in the Archaean and Proterozoic.