Middle Lower Yangtze River Research Articles

The world-class Jiangnan tungsten belt: Geologicalcharacteristics, metallogeny, and ore deposit model

The Jiangnan tungsten belt (JNB), a newly identified in the past decade, has a total resource of more than 6 Mt WO3 and still has a good potential for further prospecting. The JNB, located along the Jiangnan Massif (JM) and its eastern extensional areas, is adjacent to and parallel with the Middle-Lower Yangtze River porphyry-skarn Cu-Mo-Au-Fe belt (MLYRB) at north. Both JNB and MLYRB have the same mineralization periods, i.e., 150–135 and 130–125 Ma. The tungsten mineralization in JNB developed at the proximal contact of granite plutons, whereas the Pb-Zn±Cu veins occurs at the distal areas, exhibiting an obvious zoning in space. Apart from the Dongping quartz vein wolframite deposit, the other W deposits in the JNB belong to porphyry and skarn types. The Zhuxi scheelite skarn deposit with 3.44 Mt of WO3 is the largest one over the world. Meanwhile, the exploration of the Dahutang super-large, and Dongyuan and Yangchuling large porphyry W deposits has proven the porphyry is a new major W type except for both skarn and quartz vein types which were recognized before. Moreover, it is interesting to find unusual scheelite-bearing anorthosite and albitite dikes, which cut through the skarn ores in the Zhuxi deposit area. The scheelite-bearing albitite is proposed to crystallize from Al-, Si-, P-, W-, and F-rich residual magma whereas the scheelite-bearing anorthosite formed when the residual magma was contaminated by pure limestone in a reducing environment. The granitoids associated with W deposits and W-Mo deposits in the JNB are biotite monzonite and granodiorite, respectively. According to the petrology, geochemistry and major accessory minerals, the ore-related granitoids can be recognized as S type (or ilmenite series) with peraluminous nature and I type (or magnetite series) with metaluminous nature. Geochemical and Sr-Nd-Hf isotopic data indicate the W deposits-related granitoids were derived from the remelting of the Neoproterozoic phyllite and slate and the W-Mo deposits-related granitoids were also derived from the same strata but with input of mantle materials. According to the sources of granitoids and the skarn mineral assemblages as well as mineral chemistry it can be recognized as reduced W and the oxidized W-Mo deposits. Usually the reduced W deposit appears as large and super-large scale, such as the Zhuxi and Dahutang whereas the oxidized W-Mo as relatively smaller. A tectonic model is suggested to explain the two periods of mineralization in both JNB and MLYRB, which are corresponding to oblique subduction of Izanagi plate in 150–135 Ma at quite low angle and the extension tectonic regime of post-subduction at 130–125 Ma, respectively. The porphyry-skarn Cu-Mo-Au-Fe system in early period and apatite-magnetite system in late period along MLYRB are related to the granitoids derived from the slab subducted slab and the stagnant slab whereas tow periods of porphyry-skarn as well as quartz vein type W(Sn) deposits are associated with the granitoids which were remelted from the Neoproterozoic phyllite deduced from mantle underplated. Moreover, a deposit model is set up for the relationship among the porphyry-skarn W and W-Mo, and distal Pb-Zn-Ag±Cu veins, which can be referenced for the further prospecting in JNB and the regions with similar tectonic setting.

Ore genesis and hydrothermal evolution of the Shaxi porphyry Cu–Au deposit, Anhui province, Eastern China: evidence from isotopes (S–Sr–H–O), pyrite, and fluid inclusions

The Shaxi porphyry Cu–Au deposit is located in the northern part of the Luzong Basin on the outer edge of the southern Middle-Lower Yangtze River metallogenic belt, China. It is typical of the porphyry Cu–Au deposits in the metallogenic belt, with more than 1 Mt Cu at 0.55 wt% and 45 tons Au at 0.47 g/t. Hydrothermal alteration consists of a core of potassic alteration overprinted by a phyllic alteration zone. Propylitic alteration occurs peripheral to the potassic zone, but can also be recognized in the core of the deposit, where vein density is low. The main mineralization occurs as sulfide veinlets in the potassic zone where it is superposed by phyllic alteration. The paragenetic sequence show that chalcopyrite began to precipitate late in stage 1, associated with potassic alteration, forming quartz-sulfide veins with potassium feldspar halos, and reached a peak in stage 3, forming chalcopyrite-pyrite ± quartz ± anhydrite ± chlorite ± illite veins that accompanied phyllic alteration. Sulfur, hydrogen-oxygen and strontium isotopes, fluid inclusions, and pyrite trace element data indicate that the stage 1 assemblage associated with potassic alteration were deposited from a magmatic brine. With the change from lithostatic to hydrostatic pressure late in stage 1, the brine generated stage 1 g quartz-pyrite-chalcopyrite ± anhydrite ± bornite ± molybdenite ± potassium feldspar veins with minor copper and gold. Mixing with minor external fluids (meteoric water or gypsum-saturated groundwater) in stage 2 triggered the peripheral propylitic alteration. As the proportion of external fluid increased with the onset of hydrostatic conditions, it changed the redox state and composition of the hydrothermal system, resulting in extensive stage 3 Cu and Au precipitation with phyllic alteration. Argillic alteration associated with stage 4 veins was generated by external fluids mixed with minor hydrothermal fluid, at shallow depths.

Geochemical characteristics of pyrite in the Dabaozhuang deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China

Dabaozhuang is a pyrite deposit in the Luzong Volcanic Basin, Eastern China, and has similar exhalation-sedimentary features to volcanic massive sulfide deposits (VMS), which commonly form in seawater. To better understand the ore-forming process of this special type of deposit, we employed SHRIMP-SI and LA-ICP MS to measure sulfur isotope and trace element compositions of anhydrite and four types of pyrite from the Dabaozhuang deposit. SHRIMP in situ sulfur isotope analysis indicates a narrow range in δ34S of anhydrite, 21.0–21.7‰, and variable ranges for pyrite, 9.9–10.7‰, for pyrite vein in the deep (Py I); −9.2 to 2.0‰, for cyclic annular and oval-shaped pyrite in massive ore (Py II); 3.1–5.3‰, for massive or disseminated pyrite in the footwall tuff and hematite (Py III); and −29.7 to 30.4‰, for euhedral and coarse pyrite in the carbonate cement (Py IV). δ33S and δ36S in four types of pyrite have no abnormal values, indicating that sulfur isotope fractionation is mainly controlled by thermochemical sulfate reduction (TSR). The higher δ34S values in type I pyrite and anhydrite indicate a mixing process of magmatic fluid and evaporates at depth. Py II and IV have negative δ34S data, indicating the formation temperature of pyrite decreases because of the mixing of lake water. δ34S values in Py III are close to magmatic sulfur, which shows the igneous sulfur (tuff) is an important sulfur source for the disseminated mineralization. Cobalt and Ni content also show that the formation temperature of Py I is highest, and Py IV is lowest. This research indicates that the “VMS-like” deposits could be formed in continental volcanic lakes and are genetically related to SO42−-rich IOA (iron oxide-apatite) deposits.

Factors controlling Pt–Pd enrichments in intracontinental extensional environment: Implications from Tongshankou deposit in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China

The Tongshankou deposit is located in the southern part of the Edong district in the late Mesozoic Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Alterations related to the porphyry and skarn mineralization are pervasive and intensive. Based on the ore metal contents, four groups of ores/mineralized-rocks are divided: Cu–Mo mineralized rock, Cu–Mo ore, Cu–Mo–W ore and Cu ore. The former two groups are porphyry related, and the latter two groups are skarn related. The average grades of Au, Pt and Pd in the ores are hundreds ppb, ~2.3 ppb, and ~10 ppb, respectively. While they are ~340 ppb, ~29.3 ppb, and ~14.4 ppb in the flotation concentrations, respectively. Considering the similar geological characteristics and tectonic setting (intracontinental extensional environment (IEE)) for the Tongshankou and Fengshan PCDs, they are compared with the PC]Ds that formed in an island arc environment (IAE). Our data show that: (1) Pd and Pt contents of PCDs in IEE are much lower than those of PCDs in IAE; (2) Pd is more abundant than Pt in PCDs. Critical controlling factors for Pt–Pd enrichments in PCDs include: (1) Oxidized, mantle–derived parental magmas, which also explain why PCDs in IAE have higher Pt–Pd contents than PCDs in IEE; (2) Modes of PGE transport and precipitation (as chloride- or bisulfide- complexes) in late-stage hydrothermal fluids; (3) Behavior of sulfur during the magmatic evolution, since PGE and Au could be captured and preserved in magma due to sulfur undersaturation.

The change of cloud top height over East Asia during 2000–2018

In order to know how regional averaged cloud top height (CTH) responded to the past climatic change, the spatial and temporal variations of CTH based on MODIS data (MOD03_08_v6.0) from March 2000 to February 2018 are analyzed. The results show that the CTH in East Asia was higher in the southwest and lower in the northeast. The annual mean CTH was found to increase in East Asia at the rate of 0.020 km per year, of which, 0.035 km per year over the eastern land and 0.034 km per year over the eastern sea. The CTH changes statistically correlated with the sea surface temperature changes over the eastern sea (r = 0.68), which indicates that the CTH changes may be affected by the underlying surface. Statistically significant increasing trend of annual mean CTH was found in the latitude zone of 30°–40°N. Furthermore, CTH showed decreasing trends of about −0.030 km per year in the Middle-Lower Yangtze River Basin, Tarim Basin, Turpan Basin and northeastern Sichuan Basin in summer since more low cloud formations benefited to the decrease of CTH. In winter, the decreasing trend of CTH was found over the north of 40°N, whereas the increasing trend was found over the south of 40°N in East Asia.

Critical elements in porphyry copper deposits of China

As the world’s major source of Cu, Mo, and Au, porphyry copper deposits are magmatic-hydrothermal systems in which base and precious metals are deposited from aqueous solutions at temperatures generally >300°C. During formation of the deposits, metal-transporting fluids typically affected large volumes (up to ~100 km3) of upper crustal rocks, which has led to enormous mass redistribution and local concentration of many elements. Several critical elements, including Re, Se, and Te that are typically not found as primary ores, are locally concentrated in some porphyry copper deposits. Presently, mining and milling of porphyry copper deposits supply ~80% of the world’s Re and nearly all of the Se and Te. China has about 70 economic porphyry copper deposits, including 11 giant and 16 large deposits, with total pre-mining resources of ~78 million tonnes (Mt) Cu averaging 0.2% to 1% Cu, ~4.7 Mt Mo averaging 0.01% to 0.08% Mo, and 1400 tonnes (t) Au averaging 0.5 g/t Au. Rhenium, Se, Te, and PGE (platinum group elements) have been reported to be enriched in some porphyry copper deposits in China, but their tonnage, grade, occurrence, and resource potential remain unclear. In this study, based on a simple synthesis of critical elements in the porphyry copper deposits worldwide and geological characteristics of Chinese porphyry copper deposits, we systematically summarize these attributes of critical elements, particularly Re, in the porphyry copper deposits of China. The porphyry copper deposits in China are mainly concentrated in the following belts or districts: The Gangdese belt in southern Tibet, the Yulong belt in eastern Tibet, the Duolong district in central Tibet, the Zhongdian belt in northwestern Yunnan Province, the Central Asian orogenic belt across northern China, the Zhongtiaoshan belt in Shanxi Province, the Middle-Lower Yangtze River Valley belt, and the Dexing district in Jiangxi Province. Chinese porphyry copper deposits were formed during Paleoproterozoic, Ordovician, Carboniferous, Late Triassic to Early Cretaceous, and Eocene to Miocene, with the majority forming during the latter two time periods. Approximately 45% of the giant and ~30% of the large porphyry copper deposits in China formed in arc settings, whereas at least 35% of the giant and ~45% of the large porphyry copper deposits in China occured in post-collisional settings. The porphyry copper deposits in China typically contain ~3−313 t of Re at average grades ranging from 0.03 to 0.5 g/t Re, with ten deposits containing >50 t Re. The Re-rich porphyry copper deposits in China were mainly formed during Jurassic and Eocene to Miocene. The three largest deposits (Yulong, Jiama, and Qulong), in terms of contained Re, were formed during Eocene to Miocene and in a postcollisional setting. Rhenium in these porphyry copper deposits mainly occurs in molybdenite, and is associated with potassic and/or phyllic alteration. Average Re content in molybdenite from these deposits ranges from 30 to 1000 ppm, but shows a negative correlation with the Mo grade of the corresponding deposit. In contrast, there are only limited data on the endowment of Se, Te, and PGE for Chinese porphyry copper deposits. Similar to porphyry copper deposits worldwide, Se, Te, and PGE in Chinese porphyry copper deposits are concentrated in the sulfide minerals. The contents of Se and Te in sulfide minerals from several deposits (e.g., Bolong, Shaxi) range from ~3 to 700 ppm and are typically highest (generally >300 ppm) in Cu-bearing sulfides (e.g., bornite, chalcopyrite). Concentrations of PGE in ores of Chinese porphyry copper deposits are highly variable, with Pd+Pt contents ranging from 0.2 to 450 ppb. In summary, Chinese porphyry copper deposits, particularly those in postcollisional settings, show similar grades of Re, Se, Te, and PGE to porphyry copper deposits worldwide, indicating a large potential of these critical elements in Chinese porphyry copper deposits to meet the nation’s economic needs. To better understand the occurrence, resource potential, and enrichment processes of critical elements in the porphyry copper deposits of China, detailed case studies and regional comparisons, as well as improvements in analytical techniques, are a pressing need.

Spatial Patterns and Spatial Autocorrelations of Wetland Changes in China During 2003-2013

Wetlands play an important role in maintaining ecosystem functions. Wetlands in China have suffered intensive human disturbance, especially before 2000, resulting in great losses and degradation. Therefore, two national wetland resource surveys were carried out by the Chinese government during 1998-2003 and 2008-2013 to determine the status of wetlands, understand their dynamics, and provide substantial data that can aid scientific wetland conservation. Based on the survey data, the spatial pattern and spatial autocorrelation were explored using the standard deviation ellipse as well as global and local spatial autocorrelation statistics. GIS mapping was employed to display the results via the visualization of the spatial patterns and relationships. Results indicate that:① Changes in the wetlands of China are significant and exhibit obvious regional differences. The center of the ellipse of the total wetlands has moved to the west, and the degree of spatial differentiation between natural wetlands and artificial wetlands is increasing. There is no significant spatial autocorrelation for changes in artificial wetlands. ② The changes in natural wetlands are significantly spatially autocorrelated and clustered, which are identified by global Moran's I and local Moran's I. The hotspots of natural wetland change are concentrated primarily in Qinghai, Tibet, and Sichuan. The individual hotspot is in Inner Mongolia and the cold spot is in Henan. The difference in spatial autocorrelation between natural and artificial wetland changes indicates that natural wetland changes have shown spatial continuity, while artificial wetland changes have shown strong spatial randomness. ③ Some useful spatial associations are used to delineate wetland conservation effects. Then, three major or five minor effective protection management regions are identified. Wetland conservation efforts should be continuously strengthened and improved, especially in the middle-lower Yangtze River region of central China. The use of Moran statistics helps to reveal spatial autocorrelation and identify the conservation effects in wetland changes, which can provide a basis for decision-making in regional wetland conservation and management systems.

Theoretical performance analysis of a new hybrid air conditioning system with two-stage energy recovery in cold winter

Abstract Energy recovery technologies can effectively improve the energy efficiency of air-conditioning systems and significantly reduce building energy consumption. In this paper, a parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) is carried out theoretically based on developed models. The proposed HAC incorporates into a conventional mechanical vapor compression air conditioning system with an independent fresh air conditioner which is composed of a network of heat exchangers, including a packed bed and three air-water finned coils. Under cold winter climate, in the fresh air conditioner, a packed bed is coupled with a water-air heat exchange coil to form a total energy recovery loop. A run-around sensible energy recovery loop is also integrated in the system to produce a two-stage energy recovery effect. Moreover, a sprayer is installed upstream of the two-stage energy recovery process for fresh air humidification, and a fresh air recirculation duct is equipped for frost-free operation. In the parametric analysis, four independent affecting parameters are included: the air-to-water heat capacity ratio, the indoor temperature, the ambient temperature, and the ratio of recirculation fresh air. The energy-saving potential of the HAC is also evaluated for applications in seven typical cities located in middle-lower Yangtze River region of China over the winter period (December, January and February). The results show that compared with the conventional system with electric humidification, the HAC has an average energy saving rate of 44.0%, and its average power saving per hour is 13.41 W m−2.

Chlorite chemistry of Tongshankou porphyry-related Cu–Mo–W skarn deposit, Eastern China: Implications for hydrothermal fluid evolution and exploration vectoring to concealed orebodies

Recent years, the depletion of shallow mineral resources has drawn increasing attention to the exploration of hidden ore bodies in deep of skarn type deposits. Chemical composition of chlorite is an effective tool for tracing the hydrothermal fluid evolution, and has been increasingly used for deep-level exploration of porphyry Cu (–Au) deposits (PCDs). However, the technique was rarely applied onto (porphyry-related)-skarn deposits. The Tongshankou Cu–Mo–W deposit (0.55 Mt Cu @ 0.86%, 0.01 Mt Mo @ 0.10% and 0.12 Mt WO3 @ 0.19%) is one of the largest skarn–porphyry deposits in the Middle–Lower Yangtze River Metallogenic Belt (MLYRB) in Eastern China. In this study, new petrographic and trace element data of the hydrothermal chlorites from Tongshankou were presented to constrain the ore-fluid evolution, and to explore the vectoring potential of the concealed orebodies at Tongshankou. Four types of chlorite have been identified, i.e., G-type chlorite that replaced the original magmatic biotite or hornblende, V-type chlorite in chlorite–quartz–sulfides veins in the granodiorite porphyry (alteration zones I and II), S-type chlorite that replaced garnet in the intensive skarn alteration zone (III) and M-type chlorite–quartz–calcite–sulfides veins that cut the (dolomitic)-marble in the distal alteration zones IV and V.All the four types of chlorites are typically trioctahedral chlorite. The Fe-Mg, Tschermark and di-trioctahedral substitution mechanisms likely control the geochemical variations of the Tongshankou chlorites. Empirical thermometer indicates that the Tongshankou chlorites were crystallized at 169–322 ℃. Compared with typical metamorphic chlorites, the higher Zn and Sr contents but lower Al content in the Tongshankou chlorites can potentially distinguish the skarn-type hydrothermal chlorites from typical metamorphic ones. Compared with the chlorites in the typical PCDs, the Tongshankou G-type chlorite has higher Fe, Zn, As and Sn contents, but lower Al, Mg, Co and Cu contents, which likely reflect its protolithic and/or fluid geochemical inheritance. The Tongshankou V-, M- and S-type chlorites have high contents of mobile elements (such as Sr, Ca, Sn and B) and metals (such as Fe, Cu, As, Zn and Pb), indicating that they were directly precipitated from the hydrothermal fluids. From the granodiorite porphyry to the marble wallrocks, the spatial chlorite geochemical variations at Tongshankou indicate that the increasing Zn, Mn, Ga, Ge and Pb contents, and decreasing V, Sc and Ti contents are potential vectors toward concealed mineralized porphyries at Tongshankou. Our study highlights that the chlorite geochemistry is a potential tool for ore-fluid tracer and vectoring tool toward concealed skarn–porphyry orebodies in the MLYRB.

Short wavelength infrared (SWIR) spectroscopy of phyllosilicate minerals from the Tonglushan Cu-Au-Fe deposit, Eastern China: New exploration indicators for concealed skarn orebodies

The Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is one of the most important Cu–Au–Fe–Mo skarn–porphyry metallogenic belts in Eastern China. After several decades of mining, the shallow-level mineral resources have been gradually exhausted, which call for new exploration tools for concealed orebodies. The Tonglushan Cu–Au–Fe skarn deposit (86.3 Mt @ 1.66% Cu, 0.94 g/t Au and 39.4% Fe) is located in the western MLYRB. Skarn alteration/mineralization are mainly hosted in the contact zone between Cretaceous (~141 Ma) quartz monzodiorite (and its porphyry) and the Lower Triassic carbonate rocks. Based on the mineral assemblages and their macro/microscopic textural relationships, the Tonglushan Cu–Au–Fe mineralization/alteration can be divided into five stages: pre-ore (S1: skarn–potassic alteration), Fe ore (S2: retrograde alteration and Fe-oxides), Cu–Au ore (S3: quartz–sulfides), carbonate alteration (S4) and supergene alteration (S5). Apart from the major skarn and retrograde alteration and carbonate minerals, abundant fine-grained phyllosilicate minerals, including chlorite, white mica (illite, muscovite and phengite), smectite (montmorillonite and saponite) and kandite (kaolinite, dickite and halloysite) group minerals have been identified at Tonglushan by SWIR spectrometry. Integrating petrographic observations and SWIR spectral analysis, four alteration zones (with distinct phyllosilicate assemblages) have been distinguished from the intrusion outward: (I) ore-barren quartz monzodiorite and its porphyry (montmorillonite–illite–chlorite), (II) endoskarn close to the skarn–hydrothermal mineralization center (montmorillonite–illite–chlorite–kaolinite–dickite), (III) skarn–hydrothermal mineralization center (saponite–chlorite), and (IV) the external contact zone in (dolomitic) marble (montmorillonite–chlorite ± kaolinite ± dickite).For the Tonglushan altered rock samples, SWIR spectrometry has identified wavelength shifts in the Fe–OH, Al–OH and sub-Al–OH absorption features of chlorite, white mica–montmorillonite and kandite, respectively. Chlorite Fe–OH absorption occurs at longer wavelengths (>2,250 nm), white mica–montmorillonite Al–OH absorption occurs at unusually long (>2,212 nm) and short (<2,202 nm) wavelengths, and kandite sub-Al–OH absorption occurs at longer wavelengths (>2,170 nm) in strongly-altered skarn proximal samples. Moreover, the presence of kaolinite, dickite, saponite, actinolite, phlogopite and/or chlorite–quartz–sulfides veins in these samples can be used as new vectors to explore deep-level mineralization centers at Tonglushan. The distribution of various kinds of phyllosilicate alteration minerals at Tonglushan, especially the white mica and kandites (with higher crystallinity) in the deep contact zones, indicates that the neutral to acidic hydrothermal fluids may have been generated with the precipitation of Fe-oxides and sulfides. This study also highlights the potential of SWIR spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the MLYRB.

Processes shaping wintering waterbird communities in an intensive modified landscape: Neutral assembly with dispersal limitation and localized competition

• Processes structuring wintering waterbird communities use 2 complementary approaches. • Dispersal limitation maybe the main force shaping wintering waterbird community. • Dispersal constraints lead to competitive exclusion in isolated communities. Better understanding of the mechanisms structuring ecological communities is not only a long-term theoretical pursuit in ecology but also critical for biodiversity conservation. Here, we used two complementary approaches (β-diversity partitioning, and phylogenetic and functional null models) to explore the processes structuring wintering waterbird communities in the floodplain lakes of middle-lower Yangtze River (MLYR), China. We found that 1) neutral assembly might be the predominant process shaping the composition of wintering waterbird communities in MLYR; 2) compared to environmental factors, spatial variables, in particular those describing the large scale spatial structure among lakes, contributed more in explaining the functional and phylogenetic composition variations across the region, indicating dispersal constraints might strongly mediate neutral processes. The dispersal constraint could be imposed by movement barriers caused by anthropogenic landscape modification, site fidelity, or both; and 3) strong dispersal constraints could lead to competitive exclusion superimposed over neutrally assembly isolated communities, a hypothesis confirmed by the α- and β-null models. These findings provide strong support for the importance of conserving and improving ecological connectivity at the regional scale as well as habitat quality enhancement at lake scale.

Early Cretaceous mantle upwelling and melting of juvenile lower crust in the Middle-Lower Yangtze River Metallogenic Belt: Example from Tongshankou Cu-(Mo[sbnd]W) ore deposit

The linkage between intracontinental extension and the Early Cretaceous Cu-Mo-W polymetallic metallogenesis in the Middle-Lower Yangtze River Belt (MLYRB) has long been a subject of controversy due to the lack of convincing petrogenetic evidence to identify the nature of magmatic sources and their geological histories during extensional mantle upwelling. Here we present new zircon UPb ages, isotopic and geochemical data for granodiorites, quartz diorites and mafic microgranular enclaves (MMEs) in the Tongshankou area. Comparing the MMEs with their host porphyries, the different ratios of incompatible elements and the similar formation ages, coupled with quenched margins and the xenocrysts in the MMEs, indicate that the MMEs was most likely formed by mixing between mafic magma and their host felsic magma. The MMEs share similar geochemical and isotopic characteristics with the Cretaceous mafic rocks from MLYRB, indicating that MMEs were mostly derived from an enriched lithospheric mantle source without adakitic characteristics. Mixing of a crustal melt derived by melting of an amphibolite bearing juvenile lower crust with a mantle melt derived from melting of enriched lithospheric mantle can account for the generation of the Tongshankou prophyries. The melting of juvenile mafic lower crust and enriched lithospheric mantle is suggested to be caused by upwelling of asthenospheric mantle and the reactivity of trans-lithospheric faults in the intracontinental extensional environment. Our results therefore highlight that juvenile mafic lower crust beneath the Yangtze plate is one of the likely source for ore-forming magmatic rocks in the Early Cretaceous.

Chronology and provenance of the Yichang Gravel Layer deposits in the Jianghan Basin, middle Yangtze River Valley, China: Implications for the timing of channelization of the Three Gorges Valley

The Three Gorges Valley, linking the upper and the middle-lower Yangtze River areas is a key area for understanding the geomorphological evolution of the Yangtze River valley, especially the timing of its formation, which remains controversial and occurred following the authors to from the pre-Miocene to Late Pleistocene periods. The 100 m thick Yichang Gravel Layer (YGL), extending over an area >100 km2, is immediately observed downstream of the Three Gorges Valley in the middle Yangtze River Basin also named Jianghan Basin. Studying heavy minerals assemblage and chronology of the YGL deposits can shed lights not only on the geological origin of the sediments and the morphological evolution of the Three Gorges Valley, but also the formation of the Yangtze River Valley. In this study, 18 sediment samples carried out from six representative sections of the unconsolidated YGL and 2 samples from the underlying Neogene and Paleogene bedrocks were analyzed in order to examine their heavy mineral assemblage compositions. These assemblages were compared with modern Yangtze River sediments sampled in Yichang area (n = 5) and present-day sediments from other rivers of the Jianghan Basin (n = 6) to further identify the sediment provenance of the YGL. The statistic results indicate that the heavy minerals identified the YGL dominated by zircon, epidote, titanite, hematite, limonite and ilmenite, are similar to the assemblages observed in the 5 modern Yangtze River sediment samples but differ obviously from both underlying bedrock assemblages, containing kyanite, garnet, rutile and monazite, and other modern river sediments (Jianghan Basin), including hornblende, chlorite, tourmaline, rutile, anatase, spinel and garnet). In addition, 8 sandy samples from the YGL were dated by Electron Spin Resonance (ESR) method using Ti–Li center, showing a deposition age ranging between 1123 ± 139 and 734 ± 183 ka. Based on these observations, we propose that the YGL sediments derived from the upper Yangtze River Basin above the Three Gorges Valley, indicating that the Three Gorges Valley was channelized before 1.12 Ma ago. This result is consistent with previous provenance tracing studies of continuous deposited late Cenozoic sediment from central Jianghan Basin (since 3.0 Ma), which also constrains the incision time of the Three Gorges to ~1.1 Ma.

Geochemistry of pyrite from stratabound massive sulfide deposits, Tongling region, China: Implication for their genesis

Stratabound massive sulfide deposits are widely distributed along Middle-Lower Yangtze River metallogenic belt, in eastern China. There has much debate as to whether these deposits were associated with Late Mesozoic igneous or Carboniferous sedimentary exhalative (SEDEX). Three-type pyrites, i.e., colloform (Py1), fine-grained (Py2) and medium- to coarse-grained (Py3), from Xinqiao and Taoyuan stratabound massive sulfide deposits in Tongling region were investigated using electron probe microanalysis (EPMA), in-situ laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) and sulfur isotopic analysis. The analytic data indicate that the three-type pyrites have high S and As, and relatively consistent Au contents. The Au, Ag, Bi, Sb and Pb elements are mainly of lattice bound appearance in the Xinqiao and Taoyuan pyrites. Low Au (mainly < 5 ppm) and Ni (commonly < 10 ppm) contents, high Co/Ni (mainly > 1), Se/Tl (mainly > 1) and δ34SCDT (4.0‰ to 5.9‰) values of the studied Xinqiao and Taoyuan pyrites imply a magmatic-hydrothermal origin. High Bi (>1 ppm) and Mo contents, and low Co/Ni ratios (<0.1) of the studied Xinqiao and Taoyuan pyrites reflect a sedimentary contribution to the magmatic-hydrothermal system. Combined with previous results, the Xinqiao stratabound mineralization is most likely to be genetically with the magmatic-hydrothermal fluids by the addition of a sedimentary component.

The Role of Magma Mixing in Generating Granodioritic Intrusions Related to Cu–W Mineralization: A Case Study from Qiaomaishan Deposit, Eastern China

The newly exploited Qiaomaishan Cu−W deposit, located in the Xuancheng ore district in the MLYRB, is a middle-sized Cu–W skarn-type polymetallic deposit. As Cu–W mineralization is a rare and uncommon type in the Middle-Lower Yangtze River Belt (MLYRB), few studies have been carried out, and the geochemical characteristics and petrogenesis of Qiaomaishan intrusive rocks related to Cu–W mineralization are not well documented. We studied two types of ore-bearing intrusive rocks in the Qiaomaishan region, i.e., pure granodiorite porphyry and granodiorite porphyry with mafic microgranular enclaves (MMEs). Age characterization using zircon LA–ICP–MS showed that they were formed almost simultaneously, around 134.9 to 135.1 Ma. Granodiorite porphyries are high Mg# adakites, characterized by high-K calc-alkaline and metaluminous features that are enriched in LILEs (e.g., Sr and Ba) and LREEs, but depleted in HFSEs (e.g., Nb, Ta, and Ti) and HREEs. Moreover, they have enriched Sr–Nd–Hf isotopic compositions (with whole-rock (87Sr/86Sr)i ratios (0.706666−0.706714), negative εNd(t) values of −9.1 to −8.6, negative zircon εHf(t) values of −12.2 to −6.7, and two-stage Hf model ages (TDM2) between 1.5 and 2.0 Ga). However, compared to host rocks, the granodiorite porphyry with MMEs shows variable geochemical compositions, e.g., high Mg#, Cr, Ni, and V contents and enriched with LILEs. In addition, they have more depleted ISr, εNd(t), and εHf(t) values (0.706025 to 0.706269, −6.4 to −7.4, and −10.6 to −5.7, respectively), overlapping with regions of Early Cretaceous mafic rocks derived from enriched lithospheric mantle in the MLYRB. Coupled with significant disequilibrium textures and geochemical features of host rocks and MMEs, we propose that those rocks have resulted from mixing the felsic lower crust-derived magma and the mafic magma generated from the enriched mantle. The mixed magmas subsequently rose to shallow crust to form the ore-bearing rocks and facilitate Cu–W mineralization.

Genesis of the Baoshujian Cu-polymetal deposit in Anqing-Guichi ore-cluster area: Constraints from petrogeochemistry and geochronology

The Middle-Lower Yangtze River Valley Metallogenic Belt（ MLYB） is one of the most important metallogenic belts in China. It has long been a hot area for research. The Baoshujian Cu-polymetal deposit,as a newly discovered skarn-type deposit,is located in Anqing-Guichi ore-cluster area,Middle-Lower Yangtze River Metallogenic Belt. It has not been taken research. This paper focuses on petrogeochemistry and geochronology to explain the geneses of igneous intrusion and related Cu-Au polymetallic deposit.Results of the zircon U-Pb geochronology show that the Baoshujian intrusion was formed at ca. 148. 6 ± 3. 2 Ma,which is one of the earliest intermediate-acid ore-bearing intrusions in MLYB. The further study of this metallogenic intrusion and ore deposit will provide a rare example for magmatic activity and mineralization in Yanshanian Period in MLYB. Sulfides of ores in Baoshujian are mainly composed of galena,sphalerite,chalcopyrite and pyrite respectively. Non-metallic minerals include diopside,garnet,tremolite,quartz,albite,calcite,chlorite and epidote. The regional igneous intrusions are mainly composed of diorite and diorite porphyrite.Chemical affinity of the Baoshujian intrusion has high total K2O + Na2O contents,low Al2O3,TiO2,Fe2OT3,P2O5 contents,with enrichments of large ion lithophile elements（ U,Rb,Sr）,high field strength elements（ Nb,Ta,Ti） and light rare earths,and depletion in heavy rare earths. The intrusion has high La/Yb and Sr/Y ratios with low Yb and Y contents,belonging to adakitic affinity. All REE distribution patterns of zircon show a typical light rare earth depletion and heavy rare earth enrichment. The zircon Ti thermometer indicates that the average temperature of rock formation was 674. 3℃. The Sr-Nd-Pb isotopic characteristics of the whole rock indicate that intrusions originated from partial melting of the subducting oceanic crust,related to the far stress field of the PaleoPacific plate subduction. The δ34S values pyrite in ore range from 7. 6‰ ～ 9. 6‰,indicating that the ore-forming materials are derived from magmatic hydrothermal fluids mixed with strata. Their interaction led to the formation of minerals. The Eu anomaly characteristics and Ce4+/Ce3+ ratios of zircon indicate that the magma forming rock had high oxygen fugacity,which was beneficial to the migration of ore-forming materials such as Cu,Au and Zn,and eventually form the deposit. Conjectured from regional geological background,we suggest that the genesis of the Baoshujian intrusion was formed during the subduction of the Pacific plate,resulting in the enriched Cupolymetal adakitic magmas. The hydrothermal fluids produced by the adakitic magmas through differentiation had metasomatism with the overlying Cambrian limestone in the shallow crust,finally formed this typical Cu-polymetal skarn deposit.

Linkage of distal vein–type Au mineralization in carbonate rocks with Cu–Au skarn mineralization in the Fengshan area, Eastern China: Mineralogy and stable isotope geochemistry

Numerous limestone–hosted vein–type Au deposits (12 million tonnes at 5.0 g/t Au) are located peripheral to Cu–Au skarn deposits around the Late Jurassic granodiorite intrusions in the Fengshan area, Middle–Lower Yangtze River metallogenic belt, Eastern China. Both the Cu–Au skarn and distal vein–type Au deposits have a complex mineral assemblage, consisting of base metal sulfides, sulfosalts and Au–Ag–(Tl) telluride minerals. In the Cu–Au skarn deposits, grains of electrum, Au–Ag tellurides (hessite and petzite) coexist with Bi–Te minerals (native bismuth, tetradymite, Phase C, and aikinite), sulfides (chalcopyrite, sphalerite, and galena), occurring as grain aggregates or veinlets. In the distal vein–type Au deposits, fine–grained Au–Ag–Tl tellurides (calaverite, petzite, hessite, and Tl–bearing Au telluride) occur as ore minerals in assemblages of sulfides, and carbonate minerals. The mineralogical Bi–Te signature characterizes the skarn assemblages, while the Te–Tl signature is typical of the distal vein–type Au mineralization.Textural relations and mineral assemblages allow the recognition of five generations of hydrothermal carbonate: (1) Cu sulfides and tellurides–bearing calcite assemblages; (2) sphalerite, galena and tellurides–bearing dolomite assemblages; (3) sericite, quartz and tellurides–bearing carbonate veinlets; (4) realgar and fluorite–bearing carbonate veinlets; (5) pure calcite veinlets. Electron microprobe analysis indicates that the tellurides–bearing, ore–related carbonate contains variable Mn content (up to 80 mol.% MnCO3).The C–O isotope compositions of carbonate from the Cu–Au skarn mineralization, to the carbonate–replacement Pb–Zn and distal vein–type Au mineralization, and to the post–ore, realgar–bearing veinlets in the country rocks display a tendency towards heavier isotopic compositions with time, which could be best interpreted as the effect of fluid–rock interaction between magmatic fluid and the Triassic carbonate host rocks. New S isotope data on sulfate minerals (anhydrite, gypsum, and celestite), and C–O isotopic data suggest a common magmatic fluid source for both skarn and distal vein–type mineralization.

Numerical modeling of ore-forming processes within the Chating Cu-Au porphyry-type deposit, China: Implications for the longevity of hydrothermal systems and potential uses in mineral exploration

The Chating Cu–Au deposit is a newly discovered porphyry-type deposit within the Nanling–Xuancheng mining district of the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study uses numerical simulation to determine the key characteristics of the mineralizing system that formed the Chating deposit that traditional analysis cannot easily identify, including the duration of the mineralizing events that formed the deposit. We also outline the practical value of numerical simulation in determining the processes that operate during mineral deposit formation and how this knowledge can be used in further mineral exploration. Our simulation interlinks heat transfer, pressure, fluid-flow, chemical reaction, and material migration and indicates the presence of a temperature anomaly and modeled zones of mineralization that match the known distribution of mineralization. Our modeling further predicts a potentially mineralized zone at depths below the −1800 m level of the deposit. Combining our numerical modeling with average Cu grades and chemical reaction rates indicates that the Chating deposit formed over a period of 9600–75,000 years. These data can be used in future prospectivity modeling and mineral exploration as well as to gain insights into the genesis and duration of the system that formed the Chating porphyry Cu-Au deposit as well as porphyry mineralization in general.

3D Mineral Prospectivity Mapping with Random Forests: A Case Study of Tongling, Anhui, China

In the past few decades, a variety of data-driven predictive modeling techniques has led to a dramatic advancement in mineral prospectivity mapping (MPM). The random forests (RF) algorithm, a machine learning method, has been applied successfully to data-driven MPM. However, there are two main challenges that need to be examined. Firstly, whether RF modeling can be used for the 3D MPM. The voxel (in 3D) has replaced the pixel (in 2D) to represent geological features, and so the capability of the RF model should be tested. Secondly, when we conduct regional-scale MPM, building a suitable conceptual model has a significant influence on the results; however, mineral deposit models often focus on just deposit-scale features. These two challenges were encountered in the case study in the Tongling ore cluster, which is the most representative skarn ore-concentrated area in the Middle–Lower Yangtze River Valley Metallogenic Belt in Eastern China. Thus, 3D geological models of the Tongling ore cluster were constructed from the multiple geological datasets. Then, a conceptual model was translated into 3D predictor layers. Finally, we tested and compared the MPM capabilities of the RF and compared it with weights-of-evidence (WofE) modeling. The results indicate that RF modeling not only outperforms WofE modeling in 3D MPM, but it also has capability to assess the relative importance of different predictor layers. Further testing of this method is warranted in other areas with different scales or metallogenic model to investigate fully its efficiency.

Numerical Simulation Based Targeting of the Magushan Skarn Cu–Mo Deposit, Middle-Lower Yangtze Metallogenic Belt, China

The Magushan Cu–Mo deposit is a skarn deposit within the Nanling–Xuancheng mining district of the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study presents the results of a new numerical simulation that models the ore-forming processes that generated the Magushan deposit and enables the identification of unexplored areas that have significant exploration potential under areas covered by thick sedimentary sequences that cannot be easily explored using traditional methods. This study outlines the practical value of numerical simulation in determining the processes that operate during mineral deposit formation and how this knowledge can be used to enhance exploration targeting in areas of known mineralization. Our simulation also links multiple subdisciplines such as heat transfer, pressure, fluid flow, chemical reactions, and material migration. Our simulation allows the modeling of the formation and distribution of garnet, a gangue mineral commonly found within skarn deposits (including within the Magushan deposit). The modeled distribution of garnet matches the distribution of known mineralization as well as delineating areas that may well contain high garnet abundances within and around a concealed intrusion, indicating this area should be considered a prospective target during future mineral exploration. Overall, our study indicates that this type of numerical simulation-based approach to prospectivity modeling is both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences.