Middle-Lower Yangtze River Belt Research Articles

Rb–Sr dating and S–Sr–Nd isotopic constraints on the genesis of the Hehuashan Pb–Zn deposit in the Middle–Lower Yangtze River Metallogenic belt, China

The Hehuashan sediment-hosted Pb–Zn deposit is a large-scale (Pb + Zn＞1 Mt) deposit hosted in the Tongling mining district of the Middle-Lower Yangtze River belt (MLYB). The Pb–Zn ore bodies are composed of two main mineralization types, namely breccia type and massive type. The breccia type ore bodies are hosted by the Triassic limestone and dolostone, while the massive ore bodies are hosted by marble dolostone which are close to the diorite intrusions. The previous research showed that the Hehuashan Pb–Zn deposit is a Mississippi Valley-type (MVT) deposit formed in Middle Triassic and overprinted by late mineralization of magmatic-hydrothermal fluids in Yanshanian period. In this research, we aimed to declare the age of the late mineralization and it's relationship with diorite intrusions. The mineralization age (132.8 ± 3.1 Ma) of the massive ore rocks (late mineralization) is similar to the zircon U–Pb age of the diorite (133–130 Ma), showing that this type mineralization is contemporaneous to the Yanshanian intrusive events. Furthermore, similar initial 87Sr/86Sr values between sphalerite and diorite indicating a magmatic fluid was involved during the mineralization process and the emplacement of diorite also might have provided ore-forming materials. The heavy sulfur compositions (δ34S = +8.6‰ to +12.8‰) of the sphalerite in massive ore rocks indicate that the sedimentary sulfate may have provided reduced sulfur for sulfides precipitation by sulfate thermochemical reduction process. Sr–Nd isotopic compositions of the diorite in the Hehuashan deposit area showed that the massive Pb–Zn mineralization was related to the intrusion of diorite in an extensional tectonic setting. In summary, the Hehuashan Pb–Zn deposit composes a late Yanshanian Pb–Zn mineralization event and represents a younger Pb–Zn mineralization in the Tongling district and MLYB. The Triassic carbonates have the potential for Pb–Zn deposit exploration in the Tongling district and Middle–Lower Yangtze River belt.

Genesis of the Donggushan tungsten polymetallic deposit, central Anhui Province: A clue of diagenetic and metallogenic system of a crustal source

• The W mineralization in the Donggushan was caused by the Late Cretaceous magmatism . • Diagenetic and metallogenic system was likely to be originated from a crustal source dominated by the Northern Dabie Terrane . • The REEs of scheelite are mainly controlled by the substitution mechanism Ca 2+ + W 6+ = REE 3+ +Nb 5+ . • The ore-forming fluids were modified by the intense fluid-rock interaction. The newly discovered large-scale Donggushan tungsten polymetallic deposit with resources of 70,000 t WO 3 and 38,000 t Mo, located at the Lujiang county, center of Anhui Province, East China. The deposit is characterized by skarn W-Mo mineralization, which is developed along the external contact zone between the biotite granites and carbonate rocks. Zircon U-Pb dating yields a Late Cretaceous age of 98.3 ± 1.6 Ma for the Donggushan biotite granite. The hidden biotite granites of Donggushan is characterized by high silica and alkali but low Mg, Fe. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta and Ti), and Sr. This high-K granite has medium initial 87 Sr/ 86 Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [( 206 Pb/ 204 Pb)i, 16.452–16.533; (207Pb/204Pb)i, 15.449–15.463; ( 208 Pb/ 204 Pb)i, 36.946.335–37.097], and is characterized by low εNd(t) and εHf(t) values (−22.1 to −16.1 and −21.3 to −15.1, respectively). All these data indicate that the Donggushan biotite granite is a high-K calc-alkaline fractionated I-type granitite. This granite may have derived from a crustal source, which is dominated by the Northern Dabie Complex (NDC) mixed with the basement materials of the Taihua Group. The magmatism in the Donggushan polymetallic deposit is quite different from those in the metallogenic belts of the Qinling-Dabie Mo belt (QDMB) and Middle-Lower Yangtze River Belt (MLYB). Based on the geochemical study of REEs of scheelite, it is proposed that the substitution mechanism of Ca2+ + W6+ = REE3+ +Nb5 + occurred during the formation of scheelite. Concentrations of Eu indicate that scheelite precipitated under the oxide conditions. The variations of the Mo concentrations might be caused by the changing of oxide reduction conditions. The Sr of the scheelite and S isotopes of pyrite in the Donggushan deposit reflect a complex magmatic-hydrothermal mineralization process within the intrusion and the country rocks.

Important role of magma mixing in generating the Late Cretaceous Shima intrusion along the Middle-Lower Yangtze River belt: Evidence from petrology, geochemistry, and zircon U-Pb-Hf isotopes

Mafic microgranular enclaves (MMEs) are common in the granodiorites from the Shima intrusion in the Ningzhen region of the Middle-Lower Yangtze River belt (MLYRB). In this paper, we report new zircon U-Pb ages, mineral and whole rock geochemical and Sr–Nd–Hf isotopic data for the Shima MMEs and their host granodiorites to constrain their petrogenesis and tectonic implication. Zircon LA-ICP-MS U-Pb dating yields ages of 101.6 ± 1.1 Ma for the host granodiorites, and 101.8 ± 1.0 Ma for the MMEs, indicating formation from coeval magmas. This magmatism was contemporaneous with the latest stage (109–100 Ma) of magmatic activity within the MLYRB. Geochemically, the Shima granitoids have geochemical signatures resembling adakites, such as high Al2O3 (14.78–16.48 wt%), Sr (442–685 ppm), Na2O (>3.5 wt%), negative Nb–Ta–Ti anomalies, low Y (10.9–18.0 ppm), Yb (0.95–1.72 ppm), Sc (6.7–11.5 ppm), and resultant high Sr/Y (24.6–57.6) and La/Yb (28.3–46.6) ratios. The Shima host granodiorites are sodic, metaluminous, high-K calc-alkaline, enriched in large ion lithophile elements (LILEs; e.g., Rb, Sr, and Ba), but depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), with slightly negative to positive Eu anomalies of 0.99–1.12, (87Sr/86Sr)i of 0.7060 to 0.7061, εNd(t) values of −10.2 to −11.7 and εHf(t) of −14.1 to −16.0. The Shima MMEs have lower SiO2 (59.81–63.81 wt%), and they are also enriched in large ion lithophile elements, depleted in high field strength elements, with slightly negative to positive Eu anomalies of 0.91–1.16, (87Sr/86Sr)i of 0.7050 to 0.7061, εNd(t) values of −3.9 to −10.6 and εHf(t) of −13.0 to −15.7. Hornblende thermobarometry show that the Shima intrusion crystallised at temperatures of 769–832 °C and depths less than 11 km. All these petrographical, geochronological and geochemical results demonstrate that the Shima intrusion was likely formed through mixing of felsic melts derived from an ancient lower crust with mafic magmas derived from a metasomatized lithospheric mantle, coupled with fractional crystallization and minor wall-rock contamination. Our new data, combined with the regional tectonics and the temporal-spatial variation of the Mesozoic magmatism in the MLYRB, indicate that the Shima intrusion could be related with the back-arc extensional regime triggered by slab rollback of the paleo-Pacific plate.

Petrogenesis of Early Cretaceous granitoids and mafic microgranular enclaves from the giant Tonglushan Cu–Au–Fe skarn orefield, Eastern China

Late Mesozoic high-K calc-alkaline and high Sr/Y granitoids related to the skarn–porphyry–stratabound Cu–Au polymetallic deposits are widespread in the Middle–Lower Yangtze River Belt (MLYRB), Eastern China. However, the role of mantle-derived magmas in the petrogenesis of these granitoids remains controversial. In this study, we present new zircon U–Pb–Hf isotopes, and whole-rock geochemical and Sr–Nd isotopes data for quartz monzodiorites (porphyry), their hosting mafic microgranular enclaves (MMEs) and associated dykes from Tonglushan orefield in the MLYRB. Field relationships and geochronological data show that these intrusive rocks cluster around 141–139 Ma, indicating a short duration of magmatism, rather than a prolonged magmatism (~30 My) as previously thought. Crystallization age of the MMEs is identical to that of their quartz monzodiorite host. Petrographical and geochemical observations suggest that the MMEs represent mafic melts that injected into the quartz monzodioritic magmas, and magma mixing and (previously) fractional crystallization were involved in producing their compositional diversity. All the Tonglushan granitoids and MMEs show trace element geochemical and Sr–Nd–Hf isotope compositions similar to the coeval K-rich mafic rocks in the MLYRB. This indicates that these granitoids and MMEs were mainly sourced from the enriched subcontinental lithospheric mantle (SCLM) that metasomatized by slab derived fluids/melts, and had experienced significant fractional crystallization. The high oxygen fugacity and water content of the early Tonglushan quartz monzodiorite (porphyry) indicate melting of metasomatized SCLM and subsequently fractional crystallization and recharging/mixing in magmatic system have the potential to Cu–Au polymetallic mineralization. This study also highlights that the SCLM beneath the eastern Yangtze plate is one of the likely sources for Late Mesozoic magmatic rocks in the MLYRB.

Mineral and whole-rock chemistry of the Chating porphyry Cu--Au deposit related intrusions in the Middle-Lower Yangtze River Belt, Eastern China: Implications for magma evolution and mineralization

The Chating deposit is the largest Cu--Au porphyry deposit in the Xuancheng district of the Middle-Lower Yangtze River Metallogenic Belt. It is associated with three intrusive phases, an amphibole diorite porphyry, an ore-bearing quartz diorite porphyry and a late diorite porphyry. The amphibole diorite porphyry and quartz diorite porphyry are characterized by large ion lithophile element enrichment, depleted high field strength elements, low Yb/Lu and Y/Yb ratios, low εHf(t) (−8.29 to −12.02), εNd(t) (−6.93 to −7.42), and high 87Sr/86Sr(i) (0.705723 to 0.705802), suggesting a source comprised of both subduction-modified mantle- and crust-derived materials. The zircon U--Pb ages of the amphibole diorite porphyry (138.8 ± 3.0 Ma) and quartz diorite porphyry (137.6 ± 3.0 Ma) are consistent with their cross-cutting relationships and within error of the average molybdenite Re--Os age of 136.0 ± 1.3 Ma, suggesting that the Chating porphyry mineralization belongs to the early metallogenic event in the Middle-Lower Yangtze River Metallogenic Belt. Both the amphibole diorite porphyry and quartz diorite porphyry contain high and low Al amphiboles. The high Al amphiboles from the two intrusions show similar ranges of calculated temperatures (842 to 908 °C), pressures (143 to 229 MPa; corresponding to depths of 5.2 to 8.6 km), melt H2O contents (2 to 4 wt%), ΔNNO values (0.12 to 0.99), and Mg# (57 to 65), suggesting coeval crystallization in the same magma chamber. The low Al amphiboles with higher Mg# (68 to 75) formed at lower temperatures (711 to 812 °C) and pressures (49 to 89.3 MPa; corresponding depth of 1.9 to 3.4 km). The core-rim textures and abrupt compositional changes of amphibole and plagioclase from the amphibole diorite porphyry suggest that mafic magma was repeatedly injected into the magma chamber. In contrast, the patchy amphiboles and oscillatory zoned plagioclases in the quartz diorite porphyry may result from continuous fractional crystallization of biotite, amphibole, and plagioclase which would have increased the metal content and fO2 of the residual magma, and resulted in the exsolution of ore-forming fluids.

Genesis of Cretaceous igneous rocks and its related large scale porphyry Cu-Au mineralization in Chating, the Middle-Lower Yangtze River Metallogenic Belt: The geochemical constrains

The newly discovered large Chating porphyry Cu–Au deposit is associated with early Cretaceous intrusive rocks in the Middle-Lower Yangtze River Belt (MLYRB), eastern China. Two types of intrusive rocks in the Chating area have been identified, i.e., the quartz-diorite porphyry, related to the Cu–Au mineralization, and the diorite porphyry that is ore-barren. Zircon LA–ICP–MS U–Pb dating yields 145–136 Ma for the Chating intrusions. They both belong to High-K calc-alkaline series, with enrichments of large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletions of high field-strength elements (HFSEs) and heavy rare earth elements (HREEs), and no or slightly negative Eu anomalies. The quartz-diorite porphyry shows high Sr contents and Sr/Y ratios; low MgO, Cr and Ni contents; medium (La/Yb)N and Mg# (34.6–54.6) and low K2O/Na2O (<1) values; decoupling of Sr/Y and (La/Yb)N; and low Th/U (3.49–6.08) values, thus exhibiting characteristics of slab-derived adakitic rocks. In addition, it has slightly enriched Sr–Nd–Hf isotopes ((87Sr/86Sr)i = 0.70655–0.70717, εNd(t) = −6.9 to −8.8, and εHf(t) = −7.6 to −10.6) and high radiogenic Pb isotopes ((206Pb/204Pb)i = 18.22–18.70, (207Pb/204Pb)i = 15.63–15.66 and (208Pb/204Pb)i = 38.49–38.97), reflecting the involvement of subducted sediments in the magma source. Therefore, the fertile quartz-diorite porphyry was most likely generated by the partial melting of the slab-derived, subducted sediments and a partial degree of metasomatized mantle-derived magma with crustal assimilation. As to the barren diorite porphyry, it has similar Sr–Nd–Pb isotope and trace element features as the fertile adakitic samples. However, it shows relatively lower SiO2 contents; high contents of MgO (3.89–4.06 wt%), Cr and Ni (avg. 47.6 ppm and avg. 15.01 ppm); high Mg# (51.2–69.8); and more enriched Hf isotope characteristics (−8.5 to −12.9), which imply that this barren diorite porphyry could be generated from the partial melting of enriched metasomatised lithospheric mantle assimilated with old continental crust materials. The δ34S values of the pyrite and chalcopyrite of the ores in Chating indicate a magmatic-derived source, resembling other porphyry-skarn Cu–Au deposits in the MLYRB. The fertile Qtz-diorite porphyry adakitic rocks are characterized by higher oxygen fugacities than the barren diorite porphyry, which are closely related with the partial melting of the subducted oceanic slab in an oxidizing environment, thus making them favorable for Cu–Au mineralization.

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.

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.

Diverse lamprophyres origins corresponding to lithospheric thinning: a case study in the Jiurui district of Middle-Lower Yangtze River Belt, South China Craton

Late Mesozoic magmatic rocks that range in composition from mafic to felsic are widespread in the Jiurui district of the Middle-Lower Yangtze River belt in eastern Yangtze Craton of southeastern China. Among which the lamprophyre dikes represent mantle-derived magma and record deep mantle magmatic processes in the region. In this paper, we report a detailed study of geochronology, mineral chemistry, petrochemistry and Sr-Nd-Pb isotopes on the lamprophyres from the Nangang area in the Jiurui district, in an attempt to provide a comprehensive understanding in their petrogenesis, as well as the Mesozoic lithospheric mantle characteristics, and geodynamical control of the extensive Mesozoic magmatism in the Jiurui district. The Nangang lamprophyres belong to alkaline lamprophyre. They are characterized by low contents of SiO2 and TiO2, high Mg# values and high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE (with Nb-Ta-Ti negative anomalies). They show moderate enriched Sr-Nd isotopic compositions with initial 87Sr/86Sr values of 0.70598 to 0.70715 and εNd(t) values of −2.2 to −1.6. They also show radiogenic Pb isotopic compositions with (206Pb/204Pb)i values of 17.678 to 18.558, (207Pb/204Pb)i values of 15.544 to 15.591 and (208Pb/204Pb)i values of 38.349 to 38.664. Combining new data from the Nangang lamprophyres with those of previously published data for lamprophyres in the Jiurui (i.e. Wushan I and II lamprophyres) and Edong districts (i.e. Ruanjiawan lamprophyres), we suggest that the Jiurui lamprophyres were likely derived from partial melting of the enriched lithospheric mantle characterized by phlogopite-bearing lherzolite in spinel-garnet transition zone at 75–85km depth. The feature of enriched-mantle source region was formed by metasomatism of subducted slab-derived fluids and melts, which is likely related to the Mesozoic subduction of the paleo-Pacific plate underneath the eastern China continent and the Neoproterozoic subduction of Cathaysia Block towards the Yangtze Craton. In contrast, the Ruanjiawan lamprophyres from the Edong district have the geochemical characteristics (such as the Nb-Ta positive anomalies) which are obviously different from the Jiurui lamprophyres, and we conclude that the Ruanjiawan lamprophyres, which are located more inland than the Jiurui district, were likely derived from the depleted asthenospheric mantle that show no significant influence by the subduction-related metasomatism. Furthermore, interpretation of the Sr-Nd-Pb isotope data for the Jiurui lamprophyres suggests slightly different petrogenesis for the various lamprophyre dikes, namely, the Nangang and Wushan–I lamprophyres were derived mainly from the enriched lithospheric mantle, but with addition of depleted asthenospheric mantle materials, whereas the Wushan–II lamprophyre dikes were product of the enriched lithospheric mantle without any signature for addition of depleted asthenospheric mantle materials. Given that these lamprophyres with distinct different isotopic compositions are sympatric and coeval, we consider that in the Late Jurassic to Early Cretaceous period (ca. 155–125Ma), the lithosphere was thinned to about 75–85km depth. The enriched lithospheric mantle was heated by the underlying convective asthenosphere and underwent partial melting to generate the Wushan–II lamprophyres. Subsequently, the enriched lithospheric mantle delaminated into depleted asthenospheric mantle, followed by partial melting coupled with an intensive interaction with the asthenospheric mantle to generate the Nangang and Wushan–I lamprophyres, respectively. Towards more inland, the Ruanjiawan lamprophyres were derived from the depleted asthenospheric mantle.

Magnetite geochemistry of the Longqiao and Tieshan Fe–(Cu) deposits in the Middle-Lower Yangtze River Belt: Implications for deposit type and ore genesis

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China.Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate).Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO2, may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO2, but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO2–Al2O3–(MgO+MnO) and (Ca+Al+Mn) vs. (Ti+V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed.

Origin of andesitic rocks: Geochemical constraints from Mesozoic volcanics in the Luzong basin, South China

A combined study of whole-rock major-trace elements and Sr–Nd–Pb–Hf isotopes as well as zircon U–Pb ages and Hf–O isotopes was carried out for Mesozoic andesitic–basaltic volcanics from the Luzong basin in the Middle–Lower Yangtze River Belt, South China. The results provide insights into the origin of mantle sources above fossil Andes-type oceanic subduction zone and thus into the petrogenesis of andesitic rocks on fossil and modern continental margins. These volcanics are primarily composed of basaltic trachyandesite and trachyandesite, with small amounts of trachybasalt and trachyte. They exhibit variable contents of SiO2 (48.66–63.43wt.%), MgO (0.39–4.85wt.%), Na2O (1.22–6.07wt.%) and K2O (2.53–10.10wt.%), with highly variable K2O/Na2O ratios from 0.45 to 7.39. They are characterized by arc-like trace element distribution patterns, with significant enrichment of LILE, Pb and LREE but depletion of HFSE. They exhibit relatively enriched Sr–Nd–Pb–Hf isotope compositions, with initial 87Sr/86Sr ratios of 0.7050 to 0.7066, negative εNd(t) values of −8.0 to −3.1, negative εHf(t) values of −11.1 to −1.1, and elevated 207Pb/204Pb and 208Pb/204Pb ratios at given 206Pb/204Pb ratios. Zircon U–Pb dating yields consistent ages of 127±2 to 137±1Ma for magma emplacement through volcanic eruption. The zircon exhibits slightly high δ18O values of 5.3 to 7.6‰ and variable εHf(t) values of −13.1 to 2.6. An integrated interpretation of all these geochemical data leads to the conclusion that the Luzong andesitic–basaltic volcanics were primarily derived from partial melting of fertile and enriched, mafic–ultramafic mantle sources that are similar to those of continental arc andesites. Such mantle sources are hypothesized to form by reaction of the mantle wedge peridotite not only with hydrous felsic melts derived from partial melting of seafloor sediment but also with aqueous fluid derived from metamorphic dehydration of altered oceanic basalt during subduction of the fossil Andes-type oceanic crust beneath continental margin. As a consequence, the mantle wedge would be metasomatized by larger amounts of the felsic melts than the case for oceanic arc basalts, yielding less ultramafic lithologies for the andesitic to basaltic magmatism. Therefore, the significant incorporation of sediment-derived felsic melts into the mantle wedge is likely a key premise to the origin of andesitic rocks in fossil and modern continental margins.

The latest Yanshanian magmatic and metallogenic events in the middle-lower Yangtze River belt: Evidence from the Ningzhen region

The Ningzhen region in Jiangsu Province represents the easternmost magmatic region in the middle-lower Yangtze River belt. The formation of the polymetallic deposits has close genetic relationships with Early Cretaceous intermediate-acid intrusions. In this study, LA-ICP-MS zircon geochronology of two Mesozoic intermediate-acid intrusive rocks (including the Shima porphyritic granodiorite and Gaozi quartz diorite porphyry) in the Ningzhen region were systematically investigated. These new geochronological data demonstrate that the intermediate-acid magmatism in the Ningzhen region dates to approximately between 109 and 101 Ma. We present new 40Ar-39Ar phlogopite ages for the Cishantou skarn iron deposits that constrain the timing of the mineralisation in the Ningzhen region. The phlogopite in the Cishantou skarn deposits yielded a 40Ar-39Ar plateau age of 104±1 Ma. This result coincides with the ages of the Anjishan and Tongshan Cu (Mo) deposits in the Ningzhen region. Our high-precision geochronological data together with recent high-precision geochronological studies (such as zircon LA-ICP-MS U-Pb, zircon SHRIMP U-Pb, molybdenite Re-Os and single-mineral 40Ar-39Ar dates) reveal that there were four periods (152–135 Ma, 135–127 Ma, 127–121 Ma, 109–101 Ma) of magmatism and ore formation in the middle-lower Yangtze River metallogenic belt. The Mesozoic intermediate-acid magmatism and mineralisation in the Ningzhen region belong to the latest episode in the middle-lower Yangtze River metallogenic belt.

Late Mesozoic bimodal volcanic rocks in the Jinniu basin, Middle–Lower Yangtze River Belt (YRB), East China: Age, petrogenesis and tectonic implications

Late Mesozoic intrusive and volcanic rocks are widespread in the southeast Hubei Province, Middle–Lower Yangtze River Belt (YRB), East China. Detailed in situ zircon U–Pb and Hf isotope, elemental and Sr–Nd–Pb isotopic data are presented in this paper for Late Mesozoic volcanic rocks from the Jinniu Basin, YRB, aiming to constrain their age, petrogenesis, and tectonic implications. The Jinniu volcanic rocks show a bimodal distribution in composition, with dominant rhyolite and dacite, and subordinate basalt and basaltic andesite. New SHRIMP and LA-ICPMS zircon U–Pb ages indicate that the volcanic rocks of three Formations in the Jinniu basin were erupted at quite a short age range of about 5Ma during the Early Cretaceous (130–125Ma). The mafic rocks are moderately enriched in large-ion-lithophile-elements (LILE) (e.g., Ba, Th, U, and Pb) and light rare-earth-elements (LREE), and are characterized by negative Nb, Ta, and Ti anomalies, and relatively high TiO2 (0.72–2.06%) and Nb (9.20–26.5ppm) contents. These analyses indicate that the geochemical characteristics of the mafic rocks in the Jinniu basin are similar to worldwide Phanerozoic Nb-enriched basalt and andesites (NEBA). New in situ zircon U–Pb ages and field geological relationships demonstrate that NEBA in the southeast Hubei Province are not spatially or temporally associated with high-silica adakitic rocks, but were most likely derived from an enriched lithospheric mantle with assimilation of minor crustal materials, and then fractional crystallization during the evolution of the magma. Overall, the felsic rocks in the Jinniu basin have geochemical characteristics, and Sr–Nd–Pb signatures, and in situ zircon Hf isotopic compositions similar to those of the mafic rocks. Compared with the mafic rocks, the felsic rocks are characterized by enriched and variable concentrations of LILE and REE (e.g., Ba=33.3–1372ppm, Y=11.4–33.6ppm, YbC=5.07–18.7), and negative Eu anomalies (δEu=0.22–0.98), as well as a wide range of radiogenic Nd–Pb isotopic values with εNd (t)=−10.2 to −2.4, (206Pb/204Pb)i=17.659–18.705, (207Pb/204Pb)i=15.478–15.663, and (208Pb/204Pb)i=37.654–38.935, and in situ zircon Hf compositions of εHf (t)=−12.7 to −1.8. These features indicate that the genesis of felsic magma in the Jinniu basin is consistent with extensive fractional crystallization and large amounts of crustal contamination from an evolved mafic magma (SiO2=~55%). The bimodal volcanic rocks in this study provide convincing evidence that Early Cretaceous volcanic rocks in the YRB developed in a back-arc extensional tectonic regime.

Zircon U–Pb geochronological and Hf isotopic constraints on petrogenesis of Late Mesozoic intrusions in the southeast Hubei Province, Middle–Lower Yangtze River belt (MLYRB), East China

During the Late Mesozoic, extensive magmatism and associated ore deposits were developed in the southeast Hubei Province, Middle–Lower Yangtze River metallogenic belt (MLYRB), East China. To understand the petrogenesis of the intrusions in the area, we performed in situ zircon U–Pb and Hf isotopic analyses on 14 samples from the Fengshangdong stock, and from the Echeng, Tieshan, Wangbaoshan–Jinshandian and Yangxin batholiths. Three major suites of intrusive rocks are recognized in the southeast Hubei Province: (1) 141–146Ma granodiorite and granite porphyries (associated with 143–144Ma porphyry–skarn Cu–Mo deposits) have enriched radiogenic Hf isotopic compositions (εHf (t)=−9.5 to −1.6), comparable to those of Cretaceous pyroxene diorites, trachyandesites, and basalts (εHf (t)=−8.9 to −1.3) in the MLYRB, which were derived from an enriched lithospheric mantle. (2) Voluminous 136–143Ma gabbros, diorites, and quartz diorites (associated with 137–144Ma skarn Cu–Fe, Fe–Cu, and Au–Cu deposits) have variable Hf isotopic compositions (εHf (t)=−19.1 to −5.4), indicating an origin via the hybridization of enriched mantle-derived mafic magma and variable amounts of ancient lower-crustal components. (3) 127–133Ma diorites, quartz diorites, and granites (associated with 132–133Ma skarn Fe deposits) characterized by a wide range of εHf (t) values (−28.2 to −6.4), suggest the assimilation of various ancient lower-crustal materials by enriched mantle-derived basaltic magma. The intrusions of Suites 1 and 2 are characterized by high Sr contents (329–2087ppm), and high Sr/Yb (36–1710) and (La/Yb)N ratios(17.6–172), but low Yb contents (0.45–1.82ppm) and do not show negative Eu anomalies (δEu=0.74–1.4). The intrusions have radiogenic Sr–Nd isotopic compositions (εNd (t)=−10.0 to −3.4 and (87Sr/86Sr)i=0.7054–0.7084). Compared with the intrusions of Suites 1 and 2, rocks of Suite 3 have relatively low Sr contents (60.5–327ppm), and low Sr/Yb (33.0–315) and (La/Yb)N ratios (2.28–30.0), but relatively high Yb contents (1.04–5.17ppm) and significant negative Eu anomalies (δEu=0.22–0.73). The rocks of Suite 3 are characterized by a wide range of radiogenic Sr–Nd isotopes with εNd (t) values of −12.5 to −4.9 and (87Sr/86Sr)i=0.7057–0.7085. The proposed magma sources, combined with the geochemical and Sr–Nd isotopic differences between these three suites of intrusive rocks, indicate that Late Mesozoic magmatic activity in the southeast Hubei Province, MLYRB was associated with lithospheric thinning induced by asthenospheric upwelling at that time.

Geochemistry of Late Mesozoic dioritic porphyries associated with Kiruna-style and stratabound carbonate-hosted Zhonggu iron ores, Middle–Lower Yangtze Valley, Eastern China: Constraints on petrogenesis and iron sources

Several small Mesozoic sodium-rich dioritic porphyries associated with huge iron oxide deposits occur in the Zhonggu iron ore field, in the eastern part of the Middle–Lower Yangtze River Belt (MLYRB) in the Yangtze craton. We present bulk-rock major and trace element and Sr and Nd isotopic compositions of the three representative dioritic porphyries: the Gushan, Hemushan and Baixiangshan dioritic intrusions. These porphyries are significantly enriched in Pb and light rare earth elements (LREE), relative to high field strength elements (HFSE; Nb, Ta and Ti), coupled with the absence of significant Eu anomalies. They exhibit negative ε Nd( t) (− 5.2 to − 6.8), and highly radiogenic Pb ( 206Pb/ 204Pb = 18.27–18.45). The similar geochemical characteristics of these iron ore-bearing dioritic stocks suggest that they were derived from a common parent basaltic melt, which was produced by partial melting of the enriched lithospheric mantle. However, the parental melt experienced assimilation of Yangtze Block upper crust, accompanying the fractionation of plagioclase and clinopyroxene during ascent to the surface, which led to the extreme enrichment of iron in a highly evolved magma. The contribution of phosphorus and potential CO 2 from the country rocks might have been the crucial factor that led to liquid immiscibility and formation of the unique ore-magma type mineralization.

Geochemistry and Nd–Sr isotopic studies of Late Mesozoic granitoids in the southeastern Hubei Province, Middle–Lower Yangtze River belt, Eastern China: Petrogenesis and tectonic setting

A geochemical and isotopic study was carried out for the Mesozoic Yangxin, Tieshan and Echeng granitoid batholiths in the southeastern Hubei Province, eastern China, in order to constrain their petrogenesis and tectonic setting. These granitoids dominantly consist of quartz diorite, monzonite and granite. They are characterized by SiO 2 and Na 2O compositions of between 54.6 and 76.6 wt.%, and 2.9 to 5.6 wt.%, respectively, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), and relative depletion in Y (concentrations ranging from 5.17 to 29.3 ppm) and Yb (0.34–2.83 ppm), with the majority of the granitoids being geochemically similar to high-SiO 2 adakites (HSA). Their initial Nd ( ε Nd = − 12.5 to − 6.1) and Sr (( 87Sr/ 86Sr) i = 0.7054–0.7085) isotopic compositions, however, distinguish them from adakites produced by partial melting of subducted slab and those produced by partial melting of the lower crust of the Yangtze Craton in the Late Mesozoic. The granitoid batholiths in the southeastern Hubei Province exhibit very low MgO ranging from 0.09 to 2.19 wt.% with an average of 0.96 wt.%, and large variations in negative to positive Eu anomalies (Eu/Eu ⁎ = 0.22–1.4), especially the Tieshan granites and Yangxin granite porphyry (Eu/Eu ⁎ = 0.22–0.73). Geochemical and Nd–Sr isotopic data demonstrate that these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent. Late Mesozoic granitoids in the southeastern Hubei Province of the Middle–Lower Yangtze River belt were dominantly emplaced in an extensional tectonic regime, in response to basaltic underplating, which was followed by lithospheric thinning during the early Cretaceous.

Re–Os molybdenite and Ar–Ar phlogopite dating of Cu–Fe–Au–Mo (W) deposits in southeastern Hubei, China

The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglushan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.