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Mechanisms for invisible gold enrichment hosted within Paleoproterozoic Fe-rich metamorphic rocks (marble, biotite schist, and quartz-feldspar schist) in the Liaodong Peninsula, NE China are still unclear. In this study, we choose the Xiaotongjiapuzi deposit as a case study, and present a detailed ore deposit geology and dataset of in situ chemical compositions of Fe-sulfides to address this issue. Fe-sulfides have the following paragenesis: metamorphic pyrite (Py0), first-ore stage pyrite (Py1, Py2), and a second-ore stage comprising arsenopyrite (Apy1, Apy2) and two phases of marcasite (Mas(a-b)). Early metamorphic pyrite (Py0) has relatively low concentrations of Au (

The uplift of the Tibetan Plateau significantly affected the global climate system. However, the timing of its uplift and the formation of its vast expanse are poorly understood. The occurrence of two types of leucogranites (the two-mica leucogranites and garnet-bearing leucogranites) identified in the Ailaoshan-Red River (ASRR) shear zone suggests an extension event in the southeastern Tibetan Plateau. The age of these leucogranites could be used to constrain the timing of uplift and southeastward expansion of the plateau. Petrography, geochronology and geochemistry investigations, including Sr–Nd isotope analysis, were conducted on the two-mica leucogranites and garnet-bearing leucogranites from the ASRR shear zone. LA-ICP-MS zircon U–Pb dating indicates that these rocks were emplaced at ~27 ​Ma, implying that the Tibetan Plateau had already achieved maximum uplift prior to the late Oligocene. It subsequently started to expand southeastward as a result of crustal flow. Compared to classic metapelite-derived leucogranites from Himalaya, the two-mica leucogranites show high K2O/Na2O (1.31–1.92), low Rb/Sr, CaO, lower 87Sr/86Sr ratios (0.7089–0.7164) and higher εNd(t) (−8.83 to −3.10). This whole-rock geochemical characteristics likely indicates a mixing source origin, composed predominantly of amphibolite with subordinated metapelite, which is also evidenced by 87Sr/86Sr vs. εNd(t) diagram. However, The garnet-bearing leucogranites with high SiO2 contents (72.25–74.12 ​wt.%) have high initial 87Sr/86Sr ratios (0.7332–0.7535) and low εNd(t) (−16.36 to −18.98), indicating that they are derived from the source comprised of metapelite and results of fluexed muscovite melting under lower crustal level, which is also evidenced by the Rb–Sr–Ba systematics. These leucogranites formed from partial melting of the thickened lower crust, which resulted in the formation of granitic melt that weakened the crust. The weakened crust aided the left-lateral strike-slip movement of the ASRR shear zone, triggering the escape of the Indochina terrane in the southeastern Tibetan Plateau during the late Oligocene. Keywords: Leucogranites, Crustal flow, Southeastward expansion, Ailaoshan-red river shear zone, Tibetan plateau

Unraveling the evolution of Mississippi Valley-type (MVT) hydrothermal system is crucial for understanding ore genesis and exploration. In this paper, we take the Wusihe Pb-Zn deposit in the western Yangtze Block (South China) as a case study, using detailed ore deposit geology, quartz in situ trace elements, and sulfides in situ S-Pb isotopes, to propose a new integrated model for the evolution of MVT hydrothermal system. Four hydrothermal stages were identified in the Wusihe ore district: (I) lamellar pyrite-sphalerite; (II) disseminated, stock-work, and brecciated sphalerite-galena; (III) massive galena, and (IV) veined calcite-bitumen. Within the most representative stage (stage II), Al concentrations in quartz (Q) increase from 8.46-354 ppm (mean 134 ppm) of Q1 to 171-3049 ppm (mean 1062 ppm) of Q2, and then decrease to 3.18-149 ppm (mean 25.4 ppm) of Q3. This trend indicates the role of acid-producing processes that resulted from sulfide precipitation and acid consumption by carbonate buffering. The occurrence of authigenic non-altered K-feldspar provides further evidence that the ore-forming fluids were weakly acidic with pH values of > similar to 5.5. Moreover, new bulk delta S-34 values of sulfides (+1.8 to +14.3 parts per thousand) are overall lower than those previously reported (+7.1 to +20.9 parts per thousand), implying that in addition to thermochemical sulfate reduction (TSR), bacterial sulfate reduction (BSR) may play an important role in the formation of S2-. In situ delta S-34 values show a larger range (-4.3 to +26.6 parts per thousand), and significantly, varies within single grains (up to +12.3 parts per thousand), suggesting mixing of two isotopically distinct S2- end-members produced by TSR and BSR. The diagenetic and hydrothermal early phase (stage I) sulfides were formed within a nearly closed system of BSR, whereas the formation of late phase (stage II and stage III) sulfides was caused by the input of hydrothermal fluids that promoted TSR. New galena in situ Pb isotopic ratios (Pb-206/Pb-204 = 18.02-18.19, Pb-207/Pb-204 = 15.66-15.69, and Pb-208/Pb-204 = 38.14-38.39) suggest that the sources of mineralizing metals in the Wusihe deposit are mainly Proterozoic basement rocks. Hence, a multi-process model (i.e., basin-mountain coupling, fluid mixing, local sulfate reduction, in situ acid-producing and involvement of black shales and carbonate sequences) was responsible for the formation of the Wusihe deposit, while S2- was produced by both TSR and BSR, providing new insights into the evolution of MVT hydrothermal system.

The Wufeng and Longmaxi organic-rich shales host the largest shale gas plays in China. This study examined the petrography, rare earth element (REE) and other trace-element geochemistry, Sm-Nd geochronology, and isotope geochemistry (87Sr/86Sr, δ18O, δ13C) of fracture-cementing minerals within core samples of the Wufeng and Longmaxi Formations from the Jiaoshiba shale gas field in order to (1) characterize the mineral phases occurring in the veins (mineralized fractures); (2) determine the ages of the calcite by the Sm-Nd isochron dating method; (3) understand the sources of calcite-precipitating fluids; and (4) explore the possible mechanisms responsible for calcite vein formation in shale gas systems. The fractures hosted in the Longmaxi Formation are mineralized with quartz as the predominant fracture cement, and calcite as an intracementation phase postdating the earlier quartz cement. In contrast, the fractures hosted in the Wufeng Formation are dominantly mineralized by calcite, which occurs either as the only cement present or as a cement phase predating later quartz cement. Calcite veins within the Longmaxi Formation have a Sm-Nd isochron age of 160 ± 13 Ma and δ13C values of –4.71‰ to –3.11‰, δ18O values of 17.1‰–17.4‰, and 87Sr/86Sr values of 0.72437–0.72869. Calcite veins within the Wufeng Formation yielded a Sm-Nd isochron age of 133 ± 15 Ma and are characterized by δ13C values of –2.29‰ to –1.03‰, δ18O values of 17.3‰–17.7‰, and 87Sr/86Sr values of 0.72202–0.72648. The similarity between 87Sr/86Sr values of the calcite and those of their respective surrounding host rocks (0.72670–0.72875 of the Longmaxi shales; 0.72030–0.72648 of the Wufeng shales), combined with relatively depleted δ13C and uniform fluid δ18O isotopic features, indicates that the calcite-precipitating fluids within the Wufeng and Longmaxi Formations were derived largely from their respective surrounding host-rock sources. REE data equally indicate that the distinguishable Eu anomalies (6.20–19.35; 4.45–11.91), Y anomalies (1.03–1.50; 1.44–1.70), and Y/Ho ratios (28.80–39.16; 38.86–45.18) of calcite veins within the Longmaxi and Wufeng Formations were controlled by their respective surrounding host rocks. The Sm-Nd isochron ages and fluid inclusion data of fracture cements suggest that fracture opening and calcite precipitation in composite veins within the Wufeng and Longmaxi Formations were triggered by gas generation overpressurization.

Background Cordyceps militaris is a fungus that parasitizes insects. Compounds from C. militaris are valuable in medicine and functional food. There are many kinds of bacteria in the natural sclerotia of C. militaris. However, the community structure of microorganisms in samples from different places may be different, and the corresponding ecological functions require experimental verification. Results We used high-throughput sequencing technology to analyze bacterial 16S rRNA gene sequences in sclerotia of three samples of C. militaris from Liaoning Province, China. Pseudomonas, Pedobacter, Sphingobacterium, and Serratia were the dominant bacterial genera in the sclerotia. Pseudomonas and Pedobacter are heterotrophic, Sphingobacterium decomposes urea, and Serratia reduce nitrate. Two strains of bacteria, N-2 and N-26, were isolated from the sclerotia of the C. militaris, cultured, biochemically characterized, and identified as Stenotrophomonas maltophilia and Pseudomonas baetica, respectively. When these isolated strains were respectively cocultured with C. militaris, the mycelium biomass, mycelium pellet diameter, and cordycepin content decreased. Conclusions Bacteria in sclerotia have an important effect on the growth of C. militaris and the production of its metabolites.

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province of southwest China is one of the most important Zn–Pb ore zones in China, with ~ 200 Mt Zn–Pb ores at mean grades of 10 wt.% Zn and 5 wt.% Pb. The source and mechanism of the regional Zn–Pb mineralization remain controversial despite many investigations that have been conducted. The Wusihe Zn–Pb deposit is a representative large-scale Zn–Pb deposit in the northern SYG, which mainly occurs in the Dengying Formation and yields Zn–Pb resources of ~ 3.7 Mt. In this paper, Zn and S isotopes, and Fe and Cd contents of sphalerite from the Wusihe deposit were investigated in an attempt to constrain the controls on Zn and S isotopic variations, the potential sources of ore-forming components, and the possible mineralization mechanisms. Both the δ66Zn and δ34S values in sphalerite from the Wusihe deposit increase systematically from the bottom to the top of the strata-bound orebodies. Such spatial evolution in δ66Zn and δ34S values of sphalerite can be attributed to isotopic Rayleigh fractionation during sphalerite precipitation with temperature variations. The strong correlations between the Zn–S isotopic compositions and Fe–Cd concentrations in sphalerite suggest that their variations were dominated by a similar mechanism. However, the Rayleigh fractionation mechanism cannot explain the spatial variations of Fe and Cd concentrations of sphalerite in this deposit. It is noted that the bottom and top sphalerites from the strata-bound orebodies document contrasting Zn and S isotopic compositions which correspond to the Zn and S isotopic characteristics of basement rocks and host rocks, respectively. Therefore, the mixing of two-source fluids with distinct Zn–S isotopic signatures was responsible for the spatial variations of Zn–S isotopic compositions of sphalerite from the Wusihe deposit. The fluids from basement rocks are characterized by relatively lighter Zn (~ 0.2 ‰) and S (~ 5 ‰) isotopic compositions while the fluids from host rocks are marked by relatively heavier Zn (~ 0.6 ‰) and S (~ 15 ‰) isotopic compositions.

The Sichuan-Yunnan-Guizhou (SYG) metallogenic province, southwestern Yangtze Block, is one of the most important Zn-Pb repositories in China, with more than 200 million tons (Mt) of Zn-Pb ores. The source regions for the regional Zn-Pb mineralization in the SYG are still controversial, mostly in regard to the Emeishan flood basalts, basement rocks and host rocks. The Maozu Zn-Pb deposit is geographically close to the SYG center, which could also indicate that it is closer to the regional Zn-bearing fluid center than those deposits along the SYG margin. However, the origin of the ore-forming Zn in the Maozu deposit has not been constrained until now. In this study, the Zn and S isotopic compositions and Fe and Cd concentrations of the sphalerite from the Maozu deposit are investigated to evaluate the Zn isotopic fractionation during sphalerite precipitation, the source regions of the ore-forming zinc and sulfur, and the center of the regional Zn-bearing fluid system. It is suggested that the Zn isotopic fractionation between the sphalerite and original fluid during sphalerite precipitation could be limited due to the striking decrease in the temperature of the incoming fluid. The Zn isotopic variation of the sphalerite from four mining levels in the Maozu deposit is really small (−0.06 to +0.23‰), which could be attributed to heterogeneous Zn isotopic compositions in original incoming fluid rather than Zn isotopic fractionation during sphalerite deposition. As such, in the Maozu deposit, the Zn isotopic compositions of original hydrothermal fluid could approximately be represented by the Zn isotopic signals documented in sphalerite (−0.06 to +0.23‰). We found that the Zn isotopic signatures of incoming fluid are largely overlapped with those of the basement rocks (+0.10 to +0.34‰), signifying that the ore-forming Zn could be predominantly sourced from the basement rocks. However, in the Maozu deposit, the ore-forming sulfur is most likely derived from the sulfur-bearing evaporates hosted in the country rocks via thermochemical sulfate reduction (TSR). The contrasting sources of ore-forming zinc and sulfur suggest the mixing of Zn-bearing fluid from the basement rocks and sulfur-bearing fluid from the host rocks, which could be responsible for the sharp decrease in the temperature of the incoming fluid in the Maozu deposit. Combined with the results of previous studies, the integrally lower Zn isotopic compositions of sphalerite in the Maozu deposit compared to those deposits along the SYG margin may demonstrate that the Maozu deposit is closer to the regional Zn-bearing fluid center. If this is the case, Zn isotopes could be an effective proxy to trace the Zn source of Zn-enriched ore deposits and to identify the regional Zn-bearing fluid center of Zn-enriched metallogenic provinces.

The western margin of the Yangtze Block hosts the giant Upper Yangtze Pb-Zn metallogenic province, with the occurrence of >400 carbonate-hosted Pb-Zn deposits. More than 50% of these deposits are hosted in carbonate rocks of late Ediacaran to early Cambrian age. Although they have attracted great attention over the past two decades, it is still unclear why such carbonate sequences host so many Pb-Zn deposits and the role that the country rocks played during mineralization. The newly-discovered Maliping Pb-Zn deposit (~6 Mt @ 4.18 wt% Pb and 9.18 wt% Zn) is hosted in early Cambrian strata composed of carbonate and phosphate rocks, black shales, as well as evaporite sulfates, of which the carbonate rocks are the direct ore-hosting rocks. Evidence from mineralogy and the concentrations of ore-forming metals indicate that the phosphate rocks played an important role in providing geochemical barriers during Pb-Zn ore formation. Homogenization temperatures of the primary fluid inclusions in sphalerite and quartz range from 185 to 282 °C, and their salinities vary from 3.39 to 17.17 wt% NaCl equiv. The REE and C-O isotopes imply that the hydrothermal carbonates were formed under relatively oxidizing conditions and that the wall rocks were involved in the Pb-Zn mineralization through dissolution. Sulfur isotopic compositions (δ34S = +7.60–+31.79‰) of sulfides reveal that S2− originated from evaporite sulfates within the ore-hosting strata, and that the black shales acted as an important reducing agent during thermo-chemical reduction (TSR). Pb isotopic ratios of galena (206Pb/204Pb = 17.856–17.973, 207Pb/204Pb = 15.668–15.689 and 208Pb/204Pb = 37.953–38.101) are similar to those of Proterozoic basement rocks in the region. This implies that the basement could be the key source of mineralizing metals. Hence, we propose that: (i) The favorable lithological combination of early Cambrian phosphate rocks, black shales, carbonates and evaporites, as well as Proterozoic basement in the area, were responsible for controlling the majority of Pb-Zn deposits in the late Ediacaran-early Cambrian carbonate sequences in the western Yangtze Block; and (ii) the Maliping Pb-Zn deposit resulted from a combination of mineralized fluids, various trap structures and favorable lithologies, of which the fluids were epigenetic with low to moderate temperatures and salinities.

The superlarge Luziyuan Zn-Pb-Fe(-Cu) polymetallic deposit is located in the southern Baoshan Block of western Yunnan (SW China). The deposit contains over 4.2 million tonnes (Mt) of contained Zn + Pb metal reserves at 5.09% Zn and 2.40% Pb, and 301 Mt of Fe ore resources at 30.02% TFe. The stratiform or vein-type orebodies are hosted in the Upper Cambrian Shahechang Formation. Similar to many major Zn skarn deposits worldwide, the Luziyuan deposit shows a distinct metal zonation pattern with depth, which correlates with the different calc-silicate mineral assemblages: From Zn-Pb (sphalerite + galena) ores in marble, through Zn-Pb-Fe-Cu (sphalerite + galena + magnetite ± pyrite + chalcopyrite) ores in pyroxenoid (± clinopyroxene)-bearing skarn, to Fe-Cu (magnetite ± pyrite + chalcopyrite) ores in garnet (± clinopyroxene ± pyroxenoid)-bearing skarn. The syn-ore calcite has δ13CPDB and δ18OSMOW values of −1.0 to +0.9‰ and +10.3 to +12.7‰, respectively, suggestive of isotopic affinities to both granite and marble. δDH2O values of the fluid inclusions in the pre-ore rhodonite and the syn-ore quartz range from −81.7 to −68.8‰ and −76.6 to −56.3‰, respectively; whilst the calculated δ18OH2O values of the rhodonite, syn-ore calcite, and quartz are of +5.4 to +6.1‰, +1.4 to +3.8‰, and −5.3 to −2.0‰, respectively. This indicates that the ore-forming fluids were sourced from both magmatic and meteoric waters. δ34S values of the syn-ore sulfides (+8.9 to +12.0‰) are slightly higher than those of typical crustal-derived granites (δ34S = −4.0 to +9.0‰), but are significantly lower than those of Cambrian seawater sulfates. This indicates that the source of S is correlated with both granite and seawater sulfates. We propose that the Luziyuan Zn-Pb-Fe(-Cu) polymetallic mineralization occurred in a distal skarn system, and was genetically linked to concealed Early Cretaceous granite intrusions.

Distal massive sulfide Ag-Pb-Zn mineralization is commonly associated with proximal porphyry Mo-(Cu) systems, but the vertical evolution of Ag-Pb-Zn-(Cu)-Mo distribution within porphyry systems remains poorly understood and documented. The Laochang deposit located in the southeastern Sanjiang metallogenic belt, SW China contains both the massive sulfide Ag-Pb-Zn-(Cu) and porphyry-skarn Mo-(Cu) mineralization (1737 t Ag@222 g/t, 0.51 Mt Pb@5.1 wt%, 0.34 Mt Zn@3.1 wt%, 117, 800 t Mo@0.15 wt%, and 0.1 Mt Cu@0.2 wt%), thus representing an excellent case study. The Laochang deposit is mainly hosted in early Carboniferous volcanic rocks, late Carboniferous to early Permian carbonate rocks, and links with Eocene granite porphyry. Here, we report Rb-Sr age of sphalerite and pyrite from the massive sulfide Ag-Pb-Zn-(Cu) ores, zircon U-Pb age for the granite porphyry, C-O isotopes of hydrothermal calcite, and S-Zn isotopes of sulfide minerals to reveal the vertical distribution of Ag-Pb-Zn-(Cu)-Mo mineralization in porphyry system. The sulfides Rb-Sr age (45.1 ± 3.6 Ma) is similar to the zircon U-Pb age (44.6 ± 0.2 Ma), indicating the Ag-Pb-Zn-(Cu) mineralization has a genetic link with the granite porphyry and formed in the same system as the porphyry-skarn Mo-(Cu) mineralization. Furthermore, the C-O isotopic compositions of the hydrothermal calcite suggest a diminishing contribution of the host rocks and an increasing input of the meteoric water in the hydrothermal fluids from deep to shallow. The S-Zn isotopic compositions of the sulfide minerals indicate a magmatic source of the ore-forming elements. The δ34S values decrease, and the δ66Zn values increase with elevated levels of sampling depth, implying a Rayleigh fractionation process. This means fluids and late-stage sulfides evolved toward isotopically lighter sulfur and heavier zinc isotopes. Hence, we propose that the Laochang deposit is a porphyry system comprising distal Ag-Pb-Zn-(Cu) and proximal Mo-(Cu) mineralization. In addition, the sulfur and zinc isotopic systematics observed in this study provides a new insight into the mineralization processes of the porphyry-distal systems.

Summary Accurately determining the age of hydrothermal ore deposits is difficult, because of lack of suitable mineral chronometers and techniques. Here we present the first LA-MC-ICPMS U-Pb age of carbonates from hydrothermal Sb deposits. Three stages of hydrothermal carbonates from the giant South China Sb metallogenic belt were identified: (1) pre-ore dolomite (Dol-I), (2) syn-ore calcite (Cal-II), and (3) post-ore calcite (Cal-III). The U and Pb isotopic data show that Cal-II yielded a lower intercept age of 115.3 ± 1.5 Ma (MSWD = 2.0), suggesting a Sb mineralization that corresponds to an extension event occurred during the early Cretaceous in South China. Although Cal-III yielded an age of 60.0 ± 0.9 Ma (MSWD = 1.5), indicating a potential tectonothermal event occurred in this belt during the early Cenozoic. Hence, in situ U-Pb dating of calcite offers a new way to determine the age of hydrothermal ore deposits., Graphical Abstract, Highlights • The syn-ore calcite yielded an in situ U-Pb age of 115.3 ± 1.5 Ma • The South China antimony mineralization occurred during the early Cretaceous • Calcite in situ U-Pb dating can determine the timing of hydrothermal mineralization, Thermochronology; Isotope Geochemistry; Geochemistry Methods; Ore Geochemistry

Micro-scale isotopic compositions determined by micro-beam in situ analysis techniques are expected to provide new information for the understanding of ore genesis. Here we use the Maozu (∼20 Mt of sulfide ore, grading 7.25 wt% Zn and 4.15 wt% Pb) Zn-Pb deposit in the Upper Yangtze Zn-Pb metallogenic province as a case study, utilizing NanoSIMS in situ S, femtosecond LA-MC-ICPMS in situ Pb and conventional bulk Sr isotopes, as well as field data, aimed to reveal its origin and ore formation process. NanoSIMS in situ δ34S values of sulfide minerals from the Maozu deposit have a wider range (+5.9–+20.7‰) than that of bulk δ34 S values (+9.9–+19.9‰). Such S isotope signatures reflect the enrichment of heavy S isotopes in ore-forming fluids , and further indicate the source of S is multiple reservoirs (e.g. marine evaporites , coeval seawater, and metamorphic rocks/fluids). Pb isotopic ratios of galena determined by LA-MC-ICPMS in situ techniques have a narrower range (206Pb/204Pb = 18.20–18.21, 207Pb/204Pb = 15.69–15.71 and 208Pb/204Pb = 38.40–38.43) than that of bulk Pb isotopic ratios (206Pb/204Pb = 18.13–18.38, 207Pb/204Pb = 15.64–15.69 and 208Pb/204Pb = 38.22–38.58). This implies that in situ Pb isotopes can truly reflect the source of Pb, which is due to impurities enclosed by sulfide crystals and pollutants introduced by chemical analysis could significantly affect the quality of the bulk Pb isotopic data. Compared with previously reported Pb isotopic data of potential source rocks (i.e. late Permian Emeishan basalts , Paleozoic ore-bearing sedimentary rocks and Proterozoic basement metamorphic rocks), the in situ Pb isotopic data are significantly different from those of basalts, but are similar to those of both basements and sediments. This means that metal-rich fluids were mainly derived from and/or flowed through basements and sediments. Sphalerite separates have initial Sr isotopic ratios (0.711–0.719) that are distinctly different from those of ore formation age-corrected basalts ( 87Sr/86Sr200 Ma = 0.704–0.708) and basements (87Sr/86Sr200 Ma = 0.724–0.729), whereas partly overlap with those of age-corrected sediments (87Sr/86Sr200 Ma = 0.707–0.714). Such Sr isotope signatures suggest that hydrothermal fluids were predominantly derived from and/or flowed through basements and sediments with a certain influence from basalts. Hence, the Maozu deposit has complex source rocks that are related to the local geological setting. The mixing of metal-rich fluids (related to basements and sediments, and even basalts) and S-bearing fluids (associated with multiple S reservoirs) plays a key role in the formation of sulfide ores. Therefore, the Maozu deposit, formed during Early Mesozoic (∼196 Ma), is an epigenetic Zn-Pb deposit that hosts in carbonate rocks , occurs along fault-fold structures, and has a mixed source of mineralizing elements and associated fluids.

Strongly peraluminous granites are characterized by high A/CNK values (>1.1) and are important for understanding the regional tectonic regime. Here, we present integrated studies of zircon U–Pb ages, trace elements and Lu–Hf isotopes, whole-rock major and trace elements, and Nd isotope compositions for the newly discovered Nage granite porphyry in southeastern Guizhou Province. The porphyry has a crystallization age of 852 ± 5 Ma and shows wide ranges in SiO2 (64.5–72.51 wt%) and Al2O3 (13.08–19.34 wt%) contents, with low TiO2 (0.41–0.84 wt%) and P2O5 ( 1.1, and they have similar trace element patterns with depletion in high field strength elements (HFSE, e.g., Nb and Ta) and enrichment in large-ion lithophile elements (LILE, e.g., Rb, Th and U). Initial zircon Hf isotopes of the porphyry vary from eHf(t) = −7.6 to −0.6, whereas whole-rock Nd isotopes are relatively uniform with eNd(t) = −6.0 to −6.7. They record high zircon saturation temperatures (Tzr) (786–842 °C, mostly >810 °C), but low oxygen fugacity (log fO2 = −16 to −25, corresponding to ΔFMQ −3 to ΔFMQ −7) and emplacement pressure of 1.1), K2O/Na2O (0.7–2.6; average 1.4) and CaO/Na2O (0.2–0.8; mostly >0.5) ratios suggest that clay-poor metasedimentary rock were dominant in the source. Combined with the Nd–Hf isotopes, we suggest that the Nage granite porphyry formed by anatexis of an immature arkose and greywacke source, which was a mixture of weathered juvenile igneous materials and minor recycled ancient crustal components. The ca. 850 Ma strongly peraluminous granites, along with coeval extension-related magmatism along the southwestern margin of the Yangtze Block, indicate an extensional environment started as early as ca. 850 Ma.

In the western margin of the Yangtze Block, SW China, the Emeishan large igneous province (ELIP) is spatially associated with >400 carbonate-hosted epigenetic Pb–Zn deposits. These deposits form the giant Upper Yangtze Pb–Zn metallogenic province with >20 Mt base metals. In the southeastern part of this province, the important Pb–Zn deposits include those of the Yinchangpo, Yunluhe, Maozhachang, Tianqiao, Banbanqiao, Mangdong, Shaojiwan, Liangyan, Qingshan, Shanshulin, Nayongzhi and Guanziyao deposits. Sulfide ore bodies in these deposits are (i) hosted in late Ediacaran to middle Permian limestone, dolomitic limestone and dolostone; (ii) structurally controlled by reverse fault-anticline tectonic systems; and (iii) spatially associated with the ELIP flood basalts and mafic dikes, and early Permian, early Carboniferous and early Cambrian organic matter-rich black shales. C–O isotopic compositions suggest that dolostone and limestone, mantle-derived rocks of the ELIP, and sedimentary organic matters supplied C–O to the hydrothermal systems through water/rock (W/R) interaction. New and existing S isotopic compositions of sulfides imply multiple sources of S and the reduction of sulfate through both abiotic thermochemical (TSR) and bacterially mediated (BSR) processes. Zn isotopes indicate that the sources of Zn were most likely related to the ELIP with various contributions from sediments and basements locally. Pb isotope signatures are suggestive of derivation of Pb from basements and sedimentary rocks with variable influences from the ELIP. Sr isotopes support that mantle-derived rocks, sediments and basements were involved in Pb–Zn mineralization, and they have various contributions in different deposits. We consider that the Pb–Zn deposits in the Upper Yangtze province are the mixed products of multiple S species-bearing solutions and metal-rich fluids, both of which were derived from, flowed through or interacted with multiple lithostratigraphic units in the western Yangtze Block. The change of tectonic regimes from extension to compression after eruption of basalts of the ELIP, and then to extension during Early Mesozoic, facilitated extraction, migration, and excretion of ore-forming metals and associated fluids. Mixing of fluids and reduction geochemical barrier activated TSR, causing cyclical carbonate dissolution, CO2 degassing and recrystallization (namely carbonate buffer). All these processes triggered continuous precipitation of huge amounts of hydrothermal minerals. Underplating and eruption of ELIP basalts provided heat flow, fluids and volatiles, whereas the basalts acted as an impermeable and protective layer, and even as ore-hosting rocks. These Pb–Zn deposits have spatial and genetic association with igneous activities of the ELIP, and are characterized by high ore grades (>10 wt% Pb + Zn), high concentrations of associated metals (e.g. Cu, Ag, Ge, and Cd), and medium-low temperatures (usually

Magmatic activity plays an important role in mineralization, but little is understood of its role with respect to carbonate-hosted stratabound epigenetic Pb Zn deposits. The Fule Pb Zn deposit (~ 10 Mt of sulfide ore with mean grades of 15–20 wt% Zn + Pb), is stratigraphically placed in middle Permian strata and spatially (~ 1 m) associated with late Permian continental flood basalts of the Emeishan Large Igneous Province (ELIP). It thus provides an ideal case to investigate its genetic relationship with the ELIP. In addition, the Fule deposit is characterized by high concentrations of Ag, Cd, Ge and Ga, and contains a variety of Cu and Ni sulfide minerals. Syn-ore calcite (δ13C = + 2.57–+3.01‰) and associated fluids (δ13C = + 2.96–+ 3.40‰) have δ13C values similar to those of fresh limestone (δ13C = + 1.58–+2.63‰), but the δ18O values of calcite (+ 16.83–+19.92‰) and associated fluids (+ 7.80–+10.89‰) are distinctly lower than those of limestone (δ18O = + 21.85–+23.61‰). This means that C is mainly derived from limestone, whereas the O isotope signature may be related to water/rock (W/R) interaction between mantle and/or metamorphic fluids and limestone. δ34S values of sulfide minerals obtained by in situ NanoSIMS and conventional bulk techniques record a range of + 9.8–+23.1‰ and + 10.04–+16.43‰, respectively, reflecting the enrichment of heavy S isotopes in the ore-forming fluids and thermochemical sulfate reduction (TSR) is the principal mechanism for the formation of S2 −. Cores of sulfide crystals have much higher δ34S values than their rims, indicating a probable mixture of multiple S reservoirs and/or a dynamic fractionation of S isotopes occurred during sulfide precipitation. The uniform femtosecond (fs) LA-MC-ICPMS in situ Pb isotopic data for galena plot in the field that differs from any of the three potential sources in the region. Such signatures demonstrate that metal Pb was most likely derived from a well-mixed source of basalts, sedimentary rocks and basement rocks. We propose that (a) the enrichment in Ag, Cu, Ni, Cd, Ge and Ga, and the isotope signatures of hydrothermal minerals in the Fule region are related to fluids derived from or flowed through multiple reservoirs; (b) Emeishan magmatism provided heat, elements and associated fluids, and its basalts acted as an impermeable and protective layer; and (c) fluid mixing caused TSR, and then resulted in W/R interaction and CO2 degassing, all of which played a key role in the precipitation of hydrothermal minerals.

This introduction outlines the papers collected in the special issue “Evolution and metallogeny of the Sanjiang arc-back arc basin system in the Eastern Tethys.” The papers focus on scientific issues from Paleozoic to Cenozoic evolution and metallogeny of the Sanjiang arc-back arc basin system in the Eastern Tethys concerning tectonics, petrology, geochemistry, geochronology and mineral deposits. An evolution and metallogeny of the Sanjiang arc-back arc basin system in the Eastern Tethys is briefly introduced.

The Sanjiang Tethys region in SW China lies in the tectonic junction of the Tethys domain, and represents a key precious/base metal province in China. Based on a compilation of studies from the past decades on the formation, evolution, and metallogenesis of the tectonic units in the region, we proposed a multi-arc-basin-terrane (MABT) structural framework for the Paleo-Tethys Sanjiang region. Convergence between South China and Indochina-Pu'er blocks had led to the accretion of many island arcs and micro-continental terranes, which is different from the traditionally direct convergence between two continents. Such prolonged terrane accretion process likely formed the various metallogenetic belts that contain diverse deposit types and mineral assemblages. In this contribution, we divided the Sanjiang region into ten metallogenetic belts, according to their characteristic lithologic assemblages, structures, and interpreted tectonic settings. Subsequently, we discussed the regional tectonic-metallogenic evolution of these ten ore belts and propose their metallogenetic models. This study reveals a genetic link between the MABT system and the regional metallogenesis, which is important for future mineral exploration in this region.

The Yinchanggou Pb-Zn deposit, located in southwestern Sichuan Province, western Yangtze Block, is stratigraphically controlled by late Ediacaran Dengying Formation and contains >0.3 Mt of metal reserves with 11 wt% Pb + Zn. A principal feature is that this deposit is structurally controlled by normal faults, whereas other typical deposits nearby (e.g. Maozu) are controlled by reverse faults. The origin of the Yinchanggou deposit is still controversial. Ore genetic models, based on conventional whole-rock isotope tracers, favor either sedimentary basin brine, magmatic water or metamorphic fluid sources. Here we use in situ Pb and bulk Sr isotope features of sulfide minerals to constrain the origin and evolution of hydrothermal fluids. The Pb isotope compositions of galena determined by femtosecond LA-MC-ICPMS are as follows: 206 Pb/ 204 Pb = 18.17–18.24, 207 Pb/ 204 Pb = 15.69–15.71, 208 Pb/ 204 Pb = 38.51–38.63. These in situ Pb isotope data overlap with bulk-chemistry Pb isotope compositions of sulfide minerals ( 206 Pb/ 204 Pb = 18.11–18.40, 207 Pb/ 204 Pb = 15.66–15.76, 208 Pb/ 204 Pb = 38.25–38.88), and both sets of data plotting above the Pb evolution curve of average upper continental crust. Such Pb isotope signatures suggest an upper crustal source of Pb. In addition, the coarse-grained galena in massive ore collected from the deep part has higher 206 Pb/ 204 Pb ratios (18.18–18.24) than the fine-grained galena in stockwork ore sampled from the shallow part ( 206 Pb/ 204 Pb = 18.17–18.19), whereas the latter has higher 208 Pb/ 204 Pb ratios (38.59–38.63) than the former ( 208 Pb/ 204 Pb = 38.51–38.59). However, both types of galena have the same 207 Pb/ 204 Pb ratios (15.69–15.71). This implies two independent Pb sources, and the metal Pb derived from the basement metamorphic rocks was dominant during the early phase of ore formation in the deep part, whereas the ore-hosting sedimentary rocks supplied the majority of metal Pb at the late phase in the shallow part. In addition, sphalerite separated from different levels has initial 87 Sr/ 86 Sr ratios ranging from 0.7101 to 0.7130, which are higher than the ore formation age-corrected 87 Sr/ 86 Sr ratios of country sedimentary rocks ( 87 Sr/ 86 Sr 200 Ma = 0.7083–0.7096), but are significantly lower than those of the ore formation age-corrected basement rocks ( 87 Sr/ 86 Sr 200 Ma = 0.7243–0.7288). Again, such Sr isotope signatures suggest that the above two Pb sources were involved in ore formation. Hence, the gradually mixing process of mineralizing elements and associated fluids plays a key role in the precipitation of sulfide minerals at the Yinchanggou ore district. Integrating all the evidence, we interpret the Yinchanggou deposit as a strata-bound, normal fault-controlled epigenetic deposit that formed during the late Indosinian. We also propose that the massive ore is formed earlier than the stockwork ore, and the temporal-spatial variations of Pb and Sr isotopes suggest a certain potential of ore prospecting in the deep mining area.

Identifying alteration minerals of porphyry Cu deposits by using multispectral remote sensing data is a significant approach for ore prospecting. However, obtaining refined alteration information related to a porphyry Cu system is still challenging, especially in an area with complex geological background. In this study, the effectiveness of spectroscopic techniques for mapping alteration minerals associated with the Pulang porphyry copper deposit, SW China, which is located in high altitude and with tough terrain, were discussed by using ASTER and WorldView-3 data. The method of Principal Component Analysis (PCA) + Spectrum-Area (S-A) was developed to enhance the remote sensing information extraction of the alteration zones with quartz, sericite, chlorite and epidote. The results suggested that the extraction accuracy of porphyry alteration minerals based on WorldView-3 data with the method of PCA + S-A is significantly improved comparing with that of ASTER data. Using the method, we identified a new alteration zone caused by sericite anomalies in the Pulang deposit, which was afterward confirmed by field investigation. Hence, the PCA + S-A method based on WorldView-3 data is an effective approach for mapping alteration zones and ore prospecting in the porphyry copper system.

The Dongyuan deposit, located in the southern Anhui Province, China, is a large porphyry W–(Mo) deposit in the Jiangnan tungsten ore belt. Ore minerals are dominated by scheelite and molybdenite, which occur as disseminated or veined in biotite granite. Zircon U–Pb dating of biotite granite is 143.5 ± 0.7 Ma, which is consistent with formation age of regional tungsten mineralization. Chemical compositions of biotites from biotite granite plot near or below Ni–NiO buffer on a Fe3+–Fe2+–Mg2+diagram, suggesting that the Dongyuan biotite granite has a relatively low oxygen fugacity. The biotite granite samples are characterized by high SiO2 (68.78–70.98 wt%), Al2O3 (14.60–15.32 wt%), K2O (3.45–4.82 wt%) contents and K2O/Na2O ratios (0.98–1.59), with A/CNK ranging from 0.97 to 1.02, belonging to I-type granite. They show adakite-like geochemical features, with high Sr/Y (35.98–57.90) and (La/Yb)N (21.41–38.78) ratios but low Y (5.54–6.77 ppm) and Yb (0.44–0.55 ppm) contents, which have low MgO (0.60–0.77 wt%), Cr (15.39–28.52 ppm) and Ni (3.68–5.66 ppm) contents and Mg# (31–35) values. These samples have high initial 87Sr/86Sr ratios (0.7144–0.7160) and negative ƐNd(t) values (−9.1 to −5.5), with two-stage Nd model ages (TDM2) of 1379–1695 Ma, while the zircon ƐHf(t) values and two-stage Hf model ages (TC DM) are −6.4 to −0.7 and 1243 to 1601 Ma, respectively. These data suggest that the Dongyuan biotite granite was derived from partial melting of a thickened crustal source which had been previously produced by Neoproterozoic magmatic underplating. Combined with previously published data, we propose that the W mineralization of the Dongyuan deposit was controlled by metal-rich source region, fractional crystallization, low oxygen fugacity condition, and enrichment of fluorine volatiles, which also influenced other I-type granite-related W deposits in the Jiangnan tungsten ore belt. Furthermore, the W-related granitic rocks in this tungsten ore belt developed in a compression–extension transitional setting that was triggered by the subducted Paleo-Pacific slab roll-back.

The Qingchengzi ore filed in the Liaodong Peninsula is a polymetallic ore field, including 15 Pb-Zn deposits, 3 Ag deposits, and 17 Au deposits. The mineralization is closely related to the Mesozoic magmatism. Among those deposits, two styles of vein mineralization, namely, Pb-Zn and Ag mineralization are developed in the ore field which has reserves of 1.5 Mt of Pb + Zn, 2000 t of silver, respectively. It is still unclear whether the two styles of mineralization are related, while the knowledge carries fundamental importance to understand the mineralization events at a regional scale. To address this, we selected the Xinling Ag-Pb-Zn deposit as a case study, which demonstrates excellent two independent Pb-Zn and Ag mineralization events, but at a single deposit scale. Detailed mineralogy characterization was carried out, along with in situ geochemical and S-Pb isotope analysis of the sulfides from the two styles of mineralization. The Pb-Zn mineralization comprises 0.5–4.5 m wide veins of sphalerite-galena-pyrite which extend along strike for 20–100 m, whereas the Ag mineralization consists of 1.0–4.0 m wide veins of quartz-Ag bearing tennantite series -hessite (minor sphalerite, galena, chalcocite) which extend along strike for 30–110 m. The mineral assemblages and trace elements of sulfides indicate a Pb, Zn, and Fe-rich ore-forming fluid and a Cu, Sb, As, Ag, and Te-rich fluid. LA-ICP-MS mapping and data processing by a software package XMaptools highlight trace element remobilization of primary sphalerite as a result of the overprinting event. Sphalerite geothermometer indicates that Pb-Zn veins formed at medium temperatures (251–273 °C), whereas the Ag mineralization precipitated at low temperatures (185–246 °C). Sulfides from the Pb-Zn and Ag ore bodies have δ34S values ranging from 4.94 to 6.35‰ and 4.99 to 6.36‰, respectively, indicating that the sulfur may be derived from magmatic fluids. In situ Pb isotope analysis of sulfides reveals very different Pb isotopic ratios in Pb-Zn mineralization (lying on the Pb evolution curve of crust: μ = 9.74) when compared to the Ag mineralization (lying on the lower curve with μ = 9.5), suggesting they may form from distinct magmatic-hydrothermal systems. The observation and dataset suggest that the Pb-Zn maybe medium temperature carbonate-replacement mineralization and was overprinted by later epithermal Ag mineralization.

The Mengyejing potash deposit (MPD) is the first significant ancient potash deposit ever found in China, and it was considered to have formed during the middle to late Cretaceous. The 87 Sr/ 86 Sr ratios of potash bulk samples suggest that both bedded and veined potash orebodies of the MPD have been affected by igneous activity resulting from decompression melting of a metasomatically altered, depleted mantle from 16 Ma to present. The Rb-Sr isotopic systematics of the potash bulk samples define several apparent “isochrons” ranging from 0.609 ± 0.026 to 14.23 ± 0.63 Ma, with the maximum age being consistent with previous K-Ar ages of the K-bearing minerals from the MPD. Such isotopic signatures imply that the MPD may have been affected by multiple-stage fluid flow events since the mid-Miocene, consisting of hydrothermal fluids, continental fresh water, and/or hot spring water. It is very likely that the MPD is still affected by fluid flow-events in modern times. The mineral assemblage of halite + sylvite with minor amounts of carnallite was formed due to the recrystallization and diagenetic modification by hydrothermal fluids. Some characteristics of halite photomicrographs and inclusions and the lack of original halite chevron patterns are also supportive of the hypothesis that the deposit has undergone a diagenetic modification and dissolution–recrystallization processes.

Many Late Triassic granitic plutons are present in the eastern Yidun arc belt (EYAB), and seven have been investigated in this study. From west to east, they are: the Sucuoma (235 ± 2 Ma), Ajisenduo (224 ± 2 Ma), Jiaduocuo (218 ± 1 Ma), Cuojiaoma (219 ± 1 Ma), Maxionggou (225 ± 2 Ma), Dongcuo (222 ± 3 Ma) and Daocheng (220 ± 2 Ma) plutons. Most of the plutons have granitic compositions and contain high SiO 2 , Al 2 O 3 and K 2 O + Na 2 O, but low MgO, FeO* and CaO contents. They have similar trace element patterns, with depletion in high field strength elements (HFSE, e.g., Nb and Ta) and enrichment in large-ion lithophile elements (LILE, e.g., Rb, Th and U). Samples from the Sucuoma, Jiaduocuo and Dongcuo plutons have similar zircon Hf isotopic compositions (e Hf ( t ) = − 1.8 to − 0.3, − 3.1 to 0.4 and − 4.6 to − 1.4, respectively), whereas those from the Ajisenduo pluton exhibit more unradiogenic Hf (e Hf ( t ) = − 11.9 to − 4.8). Additionally, the Sucuoma pluton has the lowest initial 87 Sr/ 86 Sr values (0.7060–0.7090) but the least negative e Nd ( t ) (− 4.9 to − 3.3) values, whereas samples from the Ajisenduo pluton have the highest initial 87 Sr/ 86 Sr values (0.7111–0.7160), but the most negative e Nd ( t ) values (− 7.9 and − 11.3). All the samples have similar high radiogenic Pb isotopic compositions ( 206 Pb/ 204 Pb = 18.6–19.4; 207 Pb/ 204 Pb = 15.7–15.8; 208 Pb/ 204 Pb = 39.1–40.4). Based on the new geochemical data, it is determined that most of the granitoids are I-type granites and the magma source was a mixture of the metamorphic Kangding Complex, which is considered to be the basement of the western Yangtze Craton, and metasediments from the basement. However, the samples from the Ajisenduo pluton are S-type granites that were derived from partial melting of basement metasediments with only limited components from the Kangding Complex. Together with an evaluation of previously-published work, these new data indicate a dominant magmatic peak at ca. 216 Ma for the Late Triassic granitoids of the YAB and that the ages of Late Triassic magmatism become younger eastward towards the Garze-Litang suture zone. We consider that slab roll-back, with subsequent slab break-off, best explains the origin of these granitic plutons.

The Yangla Cu deposit is the largest Cu skarn deposit in the Jinshajiang tectonic belt. Based on the detailed observation of crosscutting relationships, three mineralization stages (i.e., pre-ore, ore and supergene) have been identified in the Yangla deposit. The pre-ore stage is dominated by prograde skarn. The ore stage is characterized by the precipitation of hydrous silicate minerals, Fe-oxides, Fe-Cu-Mo-sulfides, quartz and calcite, whose mineral assemblages were formed in the early and late sub-ore stages. The early sub-ore stage is marked by retrograde alteration with the deposition of hydrous silicate minerals (e.g., actinolite, epidote and chlorite), Fe-oxides, abundant Fe-Cu-Mo-sulfides, quartz and minor calcite. Whilst, the late sub-ore stage, associated with silicic and carbonate alteration, is represented by widespread thick quartz or calcite veins with disseminated pyrite, chalcopyrite, galena and sphalerite. We present new carbon-oxygen (C-O) isotopic compositions of the ore-hosting marble and hydrothermal calcite of this deposit. The hydrothermal calcite in the Yangla deposit was precipitated from both the early and late sub-ore stages. Calcite I from the early sub-ore stage is anhedral, and occurs as spot in the skarn or locally replaces the skarn minerals. Calcite II from the late sub-ore stage is distinguished by being coarse-grained, subhedral to euhedral and its occurrence in thick veins. Calcite I contains lower δ 13 C PDB (−7.0‰ to −5.0‰) and δ 18 O SMOW (7.2‰ to 12.7‰) than Calcite II (δ 13 C PDB = −4.5‰ to −2.3‰; δ 18 O SMOW = 10.7‰ to 19.4‰). In the δ 13 C PDB vs. δ 18 O SMOW diagram, the Calcite I and Calcite II data fall close to the igneous carbonatite field and between the fields of igneous carbonatite and marine carbonates, respectively. This suggests a dominantly magmatic origin for the early sub-ore fluids, and there might have been increasing carbonate wall rock involvement towards the late sub-ore stage. The ore-hosting marble (δ 13 C PDB = −4.8‰ to −0.3‰; δ 18 O SMOW = 10.2‰ to 23.9‰) also shows a positive δ 13 C PDB vs. δ 18 O SMOW correlation, which is interpreted to reflect the decreasing alteration intensity during the interactions between the hydrothermal fluids and ore-hosting carbonates. Simulated calculation suggests that both the Calcite I and Calcite II precipitated at 350 °C to 250 °C and 250 °C to 150 °C, respectively. We proposed that CO 2 degassing and water/rock interactions were likely the two major processes that precipitated the calcite and led to the observed C-O isotopic features of the Yangla Cu deposit.

The recently discovered Halatumiao magmatic Ni-Cu sulfide deposit is located in the western part of the Baolidao terrane, which represents the middle-eastern segment of the Central Asian Orogenic Belt (CAOB), Inner Mongolia, NE China. This deposit is an important case of a magmatic sulfide deposit related to Early Permian subduction magmatism in an arc setting. In this contribution, we report in-situ zircon U-Pb ages, whole-rock major and trace element and PGE data, and Os and S isotope compositions from the Halatumiao ore-bearing intrusion to constrain its genesis and relationship to the Early Permian subduction-related magmatism. The Halatumiao mafic-ultramafic intrusion is composed of wehrlite, olivine websterite and gabbro. Semi-massive and disseminated sulfide mineralization with a pentlandite + pyrrhotite + chalcopyrite assemblage occurs in both mafic and ultramafic rocks of the intrusion. In-situ dating of magmatic zircon grains separated from an ultramafic rock sample yielded a U-Pb age of 292.3 ± 1.5 Ma. This age is very close to the age of the Erbutu Ni-Cu sulfide deposit (294.2 ± 2.7 Ma) located in the western part of the northern margin of the North China craton. The high Ni/Cu ratios (6.7 in average, except one sample) of ore samples indicate that the parental magma to the Halatumiao deposit was a primitive basalt. The good positive correlation between IPGEs (Ir vs. Os, Ru and Rh) indicates that fractional crystallization of MSS is the key factor for the PGE tenors. The positive γOs(t) values (from +46 to +68) and mantle-like S isotopic compositions (δ34S mostly between −1.5 and 0.5‰), The trace element characteristics show that a minor to moderate degree of crustal contamination (5–10%) has occurred in the magma. Fractional crystallization and crustal contamination were likely the key factors for sulfide saturation in the Halatumiao mafic magma. The relatively high Ni tenors of sulfides (avg. 6.4 wt%) indicate that the Late Paleozoic mafic-ultramafic intrusions abounding in the Xing’an-Inner Mongolia region have a good potential for hosting economic Ni-Cu sulfide mineralization.

The effects of the morphology and distribution of cementite on damage formation were studied using in situ scanning electron microscopy under monotonic and cyclic tension. To investigate the effects of the morphology/distribution of cementite, intergranular cementite precipitation (ICP) and transgranular cementite precipitation (TCP) steels were prepared from an ingot of Fe-0.017 wt% C binary alloy using different heat treatments. In all cases, the damage incidents were observed primarily at the grain boundaries. The damage morphology was dependent on the cementite morphology and loading condition. Monotonic tension in the ICP steel caused cracks across the cementite plates, located at the grain boundaries. In contrast, fatigue loading in the ICP steel induced cracking at the ferrite/cementite interface. Moreover, in the TCP steel, monotonic tension- and cyclic tension-induced intergranular cracking was distinctly observed, due to the slip localization associated with a limited availability of free slip paths. When a notch is introduced to the ICP steel specimen, the morphology of the cyclic tension-induced damage at the notch tip changed to resemble that across the intergranular cementite, and was rather similar to the monotonic tension-induced damage. The damage at the notch tip coalesced with the main crack, accelerating the growth of the fatigue crack.

The Luping Pb deposit, a newly discovered Pb–(Fe–Au–Ag–Zn) polymetallic deposit close to the Cenozoic Beiya porphyry-related Au–(Fe–Cu–Pb–Zn–Ag) deposit, is located in the central Sanjiang (three rivers: Jinshajiang, Lancangjiang and Nujiang) region (western Yangtze Block) in southwestern China. Ore bodies of the Luping deposit are mainly stratiform type, host in the Middle Triassic Beiya Formation limestone and Lower Triassic Qingtianbao Formation sandstone, and occur along NNW-trending bedding-plane faults within axis of Beiya–Qinghe syncline. Three ore types, namely the Pb–Au sulfide, Fe–Au, and Au ores, can be discerned regarding their ore metal association with reserves of 2.7 million tonnes (Mt) (average grade: 3.06 wt.% Pb, 0.66 g/t Au, 41 g/t Ag, and 0.82 wt.% Zn), 3 Mt (average grade: 30 wt.% Fe, 0.96 g/t Au and 31 g/t Ag), and 0.67 Mt (average grade: 2.16 g/t Au and 13 g/t Ag), respectively. Pb–Au sulfide ores contain mainly galena, siderite, native gold, sphalerite, and pyrite, with minor chalcopyrite, pyrrhotite and arsenopyrite, and gangue minerals such as quartz, calcite and dolomite. Sulfide ore textures include mainly brecciated, banded and vein, and minor massive and disseminated. LA-ICP-MS zircon U–Pb dating of alkali-rich quartz syenite porphyry from drill holes yielded a Late Eocene (Priabonian) age (36.2 ± 0.4 Ma), broadly coeval to the zircon U–Pb ages (ca. 38 Ma–31 Ma) of alkaline porphyries and molybdenite Re–Os age (36.9 ± 0.3 Ma) from the Beiya deposit near Luping. Calcite separates have δ13CPDB and δ18OSMOW values ranging from − 5.8‰ to − 5.1‰ (average: − 5.6‰) and + 13.2‰ to + 14.7‰ (mean: + 13.6‰), respectively, suggesting association with the mantle. The sulfides have a narrow range of δ34SCDT values (+ 0.8‰–+ 2.8‰, mean + 1.8‰), which is similar to that of mantle-derived S (0 ± 3‰). 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of the sulfides range from 18.62 to 18.69, 15.66 to 15.70 and 38.92 to 39.08, respectively, similar to those of the porphyry whole-rock (206Pb/204Pb 36 Ma = 18.61–18.71, 207Pb/204Pb 36 Ma = 15.64–15.77 and 208Pb/204Pb 36 Ma = 38.88–39.32). Ore deposit geology and C–O–S–Pb isotopic data suggest that the sources of metals and ore-forming fluids were likely to be derived from the alkali-rich porphyries in the Beiya area. We propose that the Luping deposit is best classified as an epithermal Pb polymetallic deposit associated with the Beiya alkaline porphyries (ca. 36 Ma–31 Ma). Similar to other deposits related to the Cenozoic alkaline porphyries in the Jinshajiang–Red River (Ailaoshan) metallogenic belt, the Luping deposit may have been formed in the India–Eurasia post-collisional setting, when partial melting occurred in the Triassic stagnant slab that thickened the lower crust and the upper mantle, producing the alkaline magmatism and its associated mineralization.

The newly discovered Banbanqiao Zn–Pb deposit in the southeastern part of the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province is located on the western Yangtze Block, southwest China. Ore bodies of the Banbanqiao deposit are stratiform type, host in dolomitic limestone and dolostone of the Lower Carboniferous Dapu Formation and occur within the NNE-trending Banbanqiao anticline. More than 1.5 million tones (Mt) Zn–Pb ores at grades of 0.26–10.32 wt.% Pb and 0.81–28.8 wt.% Zn have been controlled until now. δ 13 C PDB and δ 18 O SMOW values of calcite separates range from −2.8‰ to −0.7‰ (average −1.1‰) and +14.1‰ to +17.0‰ (average +15.5‰), respectively. The δ 13 C PDB values are similar to those of marine carbonate rocks, but higher than those of mantle and significantly different from those of sedimentary organic matter. However, the δ 18 O SMOW values are among those of mantle, marine carbonate rocks and sedimentary organic matter. δ 34 S CDT values of sulfide separates range from +3.2‰ to +9.9‰ (average +6.5‰), unlike mantle-derived sulfur (0 ± 3‰), whilst lower than evaporites (+22‰ to +28‰) within host strata. 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb values of country shale and dolostone whole-rock samples are 18.47, 15.66 and 38.70, and 18.44–18.60, 15.66–15.85 and 38.70–39.14, respectively. Sulfide separates have 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb values ranging from 18.03 to 18.73, 15.65 to 15.78 and 38.15 to 39.14, respectively. These Pb isotopic data indicate a clearly crustal source of Pb in the plot of 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb. Total REE (ΣREE) contents of country shale and dolostone whole-rock samples are 2.63 ppm and 0.72–86.2 ppm with δEu values are 2.79 and 0.34–0.70, respectively. Pyrite, sphalerite, galena and calcite samples have ΣREE contents of 5.3–36.4 ppm, 0.29–3.39 ppm, 0.52 ppm and 22.0–41.1 ppm, respectively, and δEu values of 0.64–0.86, 0.94–2.86, 0.32 and 0.21–0.45, respectively. These rare earth elemental and isotopic data suggest that the REE, C and S in the ore-forming fluids of the Banbanqiao deposit were mainly originated from the carbonate host rocks, while the Pb and O were primarily derived from radiogenic Pb- and 18 O-depleted sources, which are most likely to be the underlying Proterozoic basement rocks. Studies on the geology, rare earth elements and isotope geochemistry indicate that the Banbanqiao deposit is a carbonate-hosted, stratiform, anticline-controlled, epigenetic and high grade Zn–Pb deposit formed by elemental compositions of mixed origin, and is a typical SYG-type deposit in the western Yangtze Block, southwest China.