Middle-Lower Yangtze Metallogenic Belt Research Articles

Infrared microthermometry of fluid inclusion in sphalerite: A case study of the Xinqiao deposit in the Middle–Lower Yangtze metallogenic belt

Infrared microthermometry allows direct measurement of fluid inclusions hosted in opaque ore minerals and can provide direct constraints on the evolution of ore-forming fluids. This study presents infrared microthermometry of spherite-hosted fluid inclusions from the Xinqiao deposit in the Middle-Lower Yangtze Metallogenic Belt and sheds new light on the ore genesis of the deposit. Considering that infrared light may lead to non-negligible temperature deviations during microthermometry, some tests were first conducted to ensure the accuracy of the microthermometric measurements. The measurement results indicated that using the lowest light intensity of the microscope and inserting an optical filter were effective in minimizing the possible temperature deviations of infrared microthermometry. All sphalerite-hosted fluid inclusions from the Xinqiao deposit were aqueous. They show homogenization temperature ranging from ~200 to 350 °C, but have two separate salinity groups (1.0–10% and 15.1–19.2% NaCl equivalent). The low-salinity group represents sedimentary exhalative (SEDEX)-associated fluids, whereas the high-salinity group results from modification by later magmatic hydrothermal fluids. Combined with published fluid inclusion data, the four-stage fluid evolution of the Xinqiao deposit was depicted. Furthermore, our data suggest that the Xinqiao deposit was formed by two-stage metallogenic events including SEDEX and magmatic-hydrothermal mineralization.

Deep Structure of Nanling-Xuancheng Ore District, Eastern China: Insights from Integrated Geophysical Exploration

As the depth of mineral exploration increases, integrated geophysical methods are increasingly playing a crucial role in prospecting deep structures at the district scale. The Nanling-Xuancheng ore district is the eighth ore district in the middle-lower Yangtze metallogenic belt in China. To reveal the deep structure of the mining district, this study mainly focuses on regional high-precision gravity and magnetic data and integrates the interpretation of magnetotelluric and reflection seismic data from a key area. By using a 2.5D joint inversion method with prior information constraints, new insights into the deep structures, tectonic deformation, and magmatic activity are obtained. Structurally, the Nanling-Xuancheng ore district presents a structural pattern of “two uplifts and two depressions” composed of multi-level thrust-overturned and folds formed by Mesozoic depressions, which has a three-layer structure in the vertical direction (shallower than 10 km). Tectonically, the main faults in the study area trend NW, which intersect with NE-trending and EW-trending faults to form a branching structure from deep to shallow. The fault intersections provide pathways for magma intrusion. The distribution of deep-seated concealed magmatic rocks shows the characteristic pattern of “a primary magma source spawning multiple subsidiary intrusion”.

The origin and ore-forming processes of the Qixiashan Pb–Zn–Ag deposit, South China: Constraints from LA–ICP–MS analysis of pyrite and sphalerite

The Qixiashan Pb–Zn–Ag deposit, located in the Nanjing–Zhenjiang area of the Middle–Lower Yangtze Metallogenic Belt (MLYB), is one of the largest PbZn deposits in Eastern China. The middle Carboniferous carbonates of the Huanglong Formation are the main host rocks of orebodies. Whether this deposit is associated with magmatic activity or sedimentary exhalative deposit is still debated due to the poor constraints on the origin of the ore materials and metallogenic processes. To address this, we analyzed the compositions of pyrite and sphalerite from different mineralization stages and depths, and the distributions of minor and trace elements within the pyrite and sphalerite crystals, using in situ laser ablation–inductively coupled plasma–mass spectrometer and scanning electron microscope analyses. Four hydrothermal stages can be identified: the pre-ore pyrite stage (stage I); Pb–Zn–Py stage (stage II); Pb–Zn–Ag stage (stage III); and carbonate stage (stage IV). The sphalerite in the deposit is typically enriched in Fe, Mn, In, and Sn, and depleted in Ge and Cd. These results are characteristic of magmatic hydrothermal activity and indicate the mineralization was related to late Yanshanian magmatic activity. The Co and Ni contents of pyrite, and the Fe, In, and Sn contents of sphalerite decrease from the early to late stages, suggesting that the temperature of the hydrothermal fluid decreased continuously. Variations in the Se content of pyrite suggest that the fO2 increased from stage I to stage II, then decreased during stage III. Detailed SEM and elemental maps show that stage-II sphalerite (Sph-1) and pyrite (Py-2) are oscillatory zoned, which we interpret to reflect pressure fluctuations and repeated local fluid phase separation during stage II. We also infer from the zoning and subsequent formation of Py-3 that magmatic hydrothermal activity increased from stage I to II, then decreased from stage II to III. In addition, changes in the In, Sn, and Fe contents of sphalerite can be useful indicators of the upward migration of ore-forming fluid and can help during prospecting for related deep magmatic rocks.

Multi-Isotopic Compositions of Ores from the Shizishan Cu–Au–Mo Orefield in the Tongling Region, Eastern China: Implications for Ore Genesis

The Middle–Lower Yangtze Metallogenic Belt (MLYMB) hosts abundant porphyry–skarn–stratabound-type Cu–Au–Mo deposits. Despite extensive research, the origin of the stratabound-type deposits, which developed at the unconformity interface between the Devonian and Carboniferous strata in the MLYMB, remains controversial. The primary debate centers on whether these deposits are the result of Carboniferous sedimentary exhalative mineralization or Mesozoic magmatic–hydrothermal mineralization. In this paper, we examine three representative deposits in the Shizishan orefield: the Chaoshan skarn-type Au deposit, the Hucun porphyry–skarn-type Cu–Mo deposit, and the Dongguashan Cu–(Au) deposit, which has a disputed genesis of its stratiform orebodies. Economically important ore minerals, such as chalcopyrite, molybdenite, and pyrrhotite, and their associated quartz and calcite, were focused on, rather than the extensively studied pyrite in the Tongling region. The ore genesis and sources of mineralized elements in the Shizishan orefield were investigated using H, O, C, S, Pb, and Cu isotopes. The H–O isotopic compositions of hydrothermal quartz from the Chaoshan, Dongguashan, and Hucun deposits indicate that the ore-forming fluids were mainly magmatic water with some meteoric water input. The C–O isotopic compositions of calcite show a large difference from the local sedimentary carbonates. The S isotopic compositions of sulfides reveal a magmatic sulfur signature. The Pb isotopic compositions in the three deposits are similar to those of the Shizishan intrusions, suggesting a magmatic source for Pb. The Cu isotopic compositions of chalcopyrite and pyrrhotite demonstrate that Cu, the primary ore-forming element, was mainly derived from magmatic–hydrothermal fluids. The stratiform orebodies display H–O–C–S–Pb–Cu isotopes consistent with the porphyry orebodies in the Dongguashan deposit, as well as in the Chaoshan and Hucun deposits, indicating a common ore genesis. From these, we conclude that the porphyry–skarn–stratabound-type Cu–Au–Mo deposits in the Shizishan orefield can be classified as a unified Mesozoic magmatic–hydrothermal metallogenic system. The stratabound-type copper sulfide deposits and the porphyry–skarn-type copper deposits in the MLYMB have a strong similarity in the source and genesis of their ore-forming elements.

Geology, geochronology, and geochemistry of the Gaojiabang tungsten-molybdenum deposit, Anhui Province, Southeast China

The Jiangnan Mo-W-Pb-Zn metallogenic belt hosts more than fifteen W-Mo and Mo deposits and is located at the margin between the Middle-Lower Yangtze metallogenic belt and the South China Continent. The recently discovered Gaojiabang W-Mo deposit, Chizhou district, Anhui Province, is the one of the largest W-Mo deposits in the belt (25.4 Mt at a grade of 0.28% WO3, 0.11 g/t Mo, with about 10,000 t of that total at an averarge grade of 6.6 g/t Au). The deposit is associated with Jurassic granite and monzonite porphyries that intruded sedimentary rocks of the Cambrian Huangboling Formation. Alteration displays a zonation from granite porphyry to wall rock. Five distinct alteration zones are recognized: deep-seated K-feldspar-biotite-quartz alteration, a quartz-sericite alteration zone, garnet-diopside-epidote alteration zone, calcite-quartz alteration zone, and zone of thermal metamorphism (hornfels). These features are comparable with porphyry Cu-Au-Mo systems. The first three zones of alteration display a close spatial relationship with W-Mo ores. Three distinct styles of W-Mo mineralization are recognized: minor vein-type W-Mo mineralization within sedimentary units; skarn W-Mo mineralization at the contact between sedimentary rocks and granite porphyry; and disseminated Mo(±W) mineralization hosted within both porphyries. The main ore minerals are scheelite, molybdenite, pyrite, pyrrhotite, and minor chalcopyrite, and display a zoned distribution in which most molybdenite occurs inside deep porphyries and the majority of the scheelite is observed inside shallow skarns and hornfels. Based on the presence of redox-indicative mineral assemblages such as pyrrhotite, molybdenite and pyrite in the absence of sulfates, we consider Gaojiabang to be a relatively reduced W-Mo porphyry-skarn system. Our new U-Pb zircon ages confirm Late Jurassic ages for granite (150.4±1.1 Ma) and monzonite porphyries (149.4±1.6 Ma). A molybdenite Re-Os age of 149.5±1.4 Ma indicates that W-Mo mineralization is closely associated with the two porphyries. This new data makes Gaojiabang the oldest deposit recognised so far in the Middle-Lower Yangtze River area, in turn inferring that the westward subduction of the Pacific Plate commenced at ∼150 Ma. Geochemical data indicate that mineralization in the Gaojiabang deposit derives from multiple sources, dominantly from magmatic rocks and basement strata via mantle-crust interaction, with the single greatest involvment of crustal materials among all deposits in the Middle-Lower Yangtze River area. Sulfides, including pyrite, pyrrhotite and molybdenite, display a wide range of δ34S between +3.8‰ to +12.1‰. The gradual increase of δ34S from inner porphyry to outer wall rock indicates contamination from crustal marine sedimentary facies as the ore-forming fluids evolved. Following the W-Mo mineralization event at Gaojiabang, emplacement of Qingyang-Jiuhua Complex at 144–127 Ma resulted in a previously unrecognized ductile deformation of porphyries, sedimentary rocks, and ores.

The influence of gold mining wastes on the migration-transformation behavior and health risks of arsenic in the surrounding soil of mined-area

Understanding the characteristic heavy metals and their migration-transformation behavior in mining areas is essential for the prevention and control of mining pollution. This study selected a gold mine in the Anqing-Guichi ore-cluster region in the Middle-Lower Yangtze metallogenic belt as the research area, the concentrations, and migration-transformation mechanisms of metalloid As and typical heavy metals (Cd, Zn, Pb, Cu, Cr, and Ni) in gold mining wastes (mine tailings and sewage sludge) and the surrounding soil (farmland soil and soil a mining area) were investigated. The results showed that the concentration of As was high in both mining wastes and soils, and the geo-accumulation index values of As in soils ranging from 1.44–6.70, indicated that As pollution was severe in the soil. Besides, a close correlation between the concentration of As and the content of iron was observed by XRF analysis, in conjunction with SEM observations, most As-bearing phases are embedded in Fe, O, and Si compounds. According to EDS and XPS results, the Fe-O-As particle was suggested to be Fe-(oxy)hydroxides with absorbed or co-precipitated As. Furthermore, the arsenic phase observed in the soils were consistent with the weathering oxidation products in the tailings, demonstrating that the mineral particles in the tailings could migrate into soils via atmospheric transport, rainwater leaching, surface runoff, etc., and consequently result in heavy metal accumulation. The sequential chemical extraction result showed that the residual state of As in the soil exceeded 60%, and As posed no risk to low risk according to the Risk assessment code result. However, due to the high concentration and high mobility of arsenic, its environmental impact cannot be ignored even if its bio-accessibility in mined area soil is low.

Crustal Structure and Anisotropy in the Lower Yangtze Region and its Metallogenic Implications

In this study, we performed receiver function profiling and fitted harmonic functions to the arrival time variations of Pms phases to calculate the crustal seismic anisotropy with delay time and fast polarization direction, using broadband seismic data obtained from 55 temporary stations in two linear profiles and 39 stations in the Lower Yangtze and adjacent region. Moreover, we determined the crustal thickness and Poisson’s ratio using a novel H-κ-c stacking method. Our results revealed that the Middle-Lower Yangtze Metallogenic Belt and the north east section of the Qinzhou-Hangzhou Metallogenic Belt are characterized by Moho upliftment (<32 km), a relatively high Poisson’s ratio (>0.26), local lithospheric thinning (<70 km), and a pattern of deep faults that connect the crust and asthenosphere and serve as conduits for magma upwelling. The NE-SW fast polarization direction was consistent with the SKS splitting results, and the average delay time was 0.45 s. Moreover, underplating of deep magma and upwelling along the weak zone caused local Moho uplift and ductile shear of the lower crust, resulting in the directional arrangement of amphibole and other minerals, which may be the controlling mechanism for the crustal anisotropy in the study area. The variations in crustal structure and anisotropy characteristics indicated that in the context of the northeastern Paleo-Pacific plate subduction, the existence of weak lithospheric zones and the northeastern asthenospheric flow are important conditions for metal supernormal enrichment in the Lower Yangtze region.

Spatial-temporal heterogeneity of magma emplacement process and its constraints on localization of associated orebody: A case study in the Shizishan orefield of the Tongling Ore Cluster, East China

We present a study on the Dongguashan quartz diorite stock which is the largest Early Cretaceous intrusion associated with skarn-porphyry polymetallic ore deposit in the Tongling Ore Cluster, Middle-Lower Yangtze Metallogenic Belt in East China. The Dongguashan quartz diorite show massive texture without obvious foliation, and intrusive contact was locally observed inside of the stock. The anisotropy of magnetic susceptibility (AMS) results of the stock show two distinct groups. The Group I (G-I) is dominated by NE-SW-striking magnetic foliation with variably oriented magnetic lineation. The Group II (G-II) that intruded into G-I is characterized by steep NW-SE-striking magnetic foliation and lineation, which are parallel to the vein-like orebody developed in the stock. The 3D geometrical modelling of the stock displays a triangular shape in plan-view with an eastward bulge and irregular stock boundary in the eastern side and the contact surface is steeper in the west than that in the east, denoting that the stock was constructed with an eastward magma accretion trend. Furthermore, the Dongguashan quartz diorite has a wide range of composition and geochronological data, suggesting a multiple magma pulses emplacement model. Accordingly, we propose that the Dongguashan stock was constructed by at least two stages magma pulses. The earlier stage magma pulses intruded along the NE-SW-striking pre-emplacement structures in the country rock and partly intruded into the lithological and mechanical discontinuous interfaces which yielded the stratabound skarn orebody. The eastward magma accretion produced a highly deformed and longer heated country rock on the eastern side of the stock, favoring the orebody development along the eastern stock-country rock contact interface. The late-stage magma pulse and the parallelism among the trend of magnetic foliation of G-II, extensional structure and vein-like orebody suggest that the vein-type orebodies may controlled by both magma emplacement and regional tectonics.

Textures, trace elements and Pb isotopes of pyrite from the Donggushan tungsten polymetallic deposit, eastern China: Deciphering the source of a skarn tungsten polymetallic deposit

The Donggushan tungsten polymetallic deposit is located near the northern margin of one of the most important ore deposit belts in China; the Middle - Lower Yangtze Metallogenic Belt (MLYB). The source and genesis of mineralization in the Donggushan deposit is poorly understood and is investigated using pyrite textures and geochemistry. Two types of pyrite and two subtypes were recognized, based on the location within the ore body, mineral assemblages, textures and geochemistry. Pyrite 1a occurs in the cores of pyrite crystals in the tungsten orebody, at depth within the deposit, near the intrusive rocks. It is characterized by high Ni and low contents of other trace elements and is overgrown by Py1b which has low Ni and higher trace elements. Pyrite 2a is characterized by moderate As and higher trace elements than those in Pyrite 1. It occurs in the cores of pyrite crystals in the shallow zinc-lead orebody. This pyrite is overgrown by Pyrite 2b characterized by higher trace elements. The trace elements, textures and inclusions in these pyrites suggest a progressive decrease in temperature, with Pyrite 1a forming at 350 °C through to Pyrite 2b forming at < 250 °C. The Pb isotopic compositions in the pyrites indicate that Pb in the deep tungsten ore body was derived from Yangtze upper crust (Dongling basement) but that Pb in the shallower ore body was sourced from the Dabie Orogen lower crust. The data supports a model whereby intra-continental subduction was the main geodynamic process controlling the mineralization of the Donggushan deposit.

Geochemical characteristics of chlorite in the Luohe iron deposit in the middle-lower Yangtze metallogenic Belt, Eastern China

Chlorite is an alteration mineral commonly found in magmatic-hydrothermal deposits. In recent years, trace elements in chlorite have become an effective way to estimate the location of the mineralization centre (intrusive rocks) in many porphyry deposits, however, the usefulness of this approach has not yet been evaluated for iron oxide apatite (IOA) deposits. The Luohe iron deposit, located in the northwestern part of the Luzong (Lujiang-Zongyang) Basin of the Middle-Lower Yangtze Metallogenic Belt (MLYB), is the largest iron deposit in the MLYB. It is composed of a shallow (380–850 m) and a deep (1350–1800 m) ore body. However, no core intrusive rock has been found in the exploration area, which restricts field exploration and theoretical research of its metallogenic model. Based on the geological characteristics of the Luohe iron deposit, samples were collected from different locations along a 545 m long exploration tunnel and from four drillholes at depths ranging between 870 and 1850 m. The samples were analysed using in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to identify the trace element characteristics of chlorite. The results showed significant negative correlations of Fe vs Na, Fe vs Si, and Fe vs K, and a positive correlation of Fe vs Mg in chlorite. The ratios Ti/Pb, Mg/Sr, Ni/V, and Ti/Sr gradually increased from east to west, with the values highest in chlorite of drillhole zk2-1, and decreased northward and southward. The results confirm that the spatial distribution pattern of trace elements in chlorite in IOA deposits is similar to that in porphyry deposits. Therefore, a methodology similar to that for porphyry deposits was herein adopted for estimating the position of the mineralization centre in the Luohe iron deposit. According to the Ti/Sr ratios in Luohe chlorite, we estimate that the concealed mineralisation centre is located southwest of the lower ore body at a depth of approximately 2300–2500 m.

Research and Application of Micromotional Exploration in the Middle-Lower Yangtze Metallogenic Belt of China

Micromotion is the daily tiny vibration of the earth’s surface. Micromotional exploration can use the surface wave information of micro motion to study the shallow structure of underground media. In this study, we collected microtremor data at 68 stations in the Middle-Lower Yangtze Metallogenic Belt (MLYMB) and determined the resonant frequency and obtained the distribution of sedimentary thickness in this area by using H/V spectral ratio. According to the results of H/V, the sedimentary layer in the basin is thick, and the predominant frequency of the basin is 0.05 - 0.1 Hz. There are no obvious lateral changes in the impedance interface between bedrock and sedimentary layer in this area. The basement of Tongling, Anqing and Luzhou mining areas and their adjacent areas is Kongling-Dongling type basement, which is composed of a set of metamorphic core complex. The predominant frequency is 0.05 - 0.1 Hz. The sedimentary thickness gradually thinned from 3800 m in the west to 2100 m in the East. Moreover, this article used SPAC (spatial autocorrelation) method to obtain the S-wave velocity structure of the mining area near Luzong. The SPAC method reveals that the depth of the interface between the loose sediments and the volcanic rocks is about 600 m in the study area near the Luzhou mining area in the Middle-Lower Yangtze Metallogenic Belt, and the average depth of the interface between the volcanic rock section and the intrusive complex section is about 1000 m. The thickness of the intrusive rock is more than 2500 m. Tourmaline is developed in the interior of the intrusive rock, which may have better exploration value.

Genetic Types, Spatiotemporal Distribution of Ore Deposits and Sources of Ore‐forming Materials in the Xuancheng Area, Anhui Province

AbstractIn recent years, several large and medium‐sized ore deposits have been discovered in the shallow cover of Xuancheng, Anhui Province, indicating that this area has a productive metallogenic geological background and may be a potential prospecting region. Based on systematic investigation, the geological and mineralization characteristics of porphyry Cu‐Au deposits and skarn Cu‐Mo‐W deposits in this region have been summarized. Zircon U‐Pb dating (LA‐ICP‐MS) of the Chating quartz‐diorite porphyry and the Kunshan biotite pyroxene diorite yield concordia ages of 145.5 ± 2.1 Ma and 131.8 ± 2.1 Ma, respectively. Meanwhile, the Re‐Os dating analyses for molybdenite from the Shizishan and Magushan skarn Cu‐Mo deposits yielded 133.81 ± 0.86 Ma and 143.8 ± 1.4 Ma ages, respectively. When viewed in conjunction with previous studies, it is suggested that twostage (the early stage of 145–135 Ma and the late stage of 134–125 Ma) magmatism may have occurred during the Mesozoic in Xuancheng region. Early stage intrusive rocks are distributed along both sides of the Jiangnan deep fault (JDF). The intrusive rocks to the north of the JDF are mainly quartz‐diorite porphyry and granodiorite (porphyry) rocks, related to porphyry Cu‐Au deposits and skarn‐type Cu‐Mo‐W deposits. These deposits belong to the first stage of the porphyry‐skarn copper gold metallogenic belt of the Middle‐Lower Yangtze Metallogenic Belt (MLYB), associated with the high potassium calc‐alkaline intermediate‐acid intrusions. The magmatic and ore‐forming materials are mainly derived from the enriched lithospheric mantle. South of the JDF, the Magushan granodiorite is a representative intrusive rock of the first stage I‐type granite, which hosts the Magushan Cu‐Mo skarn deposit, similar to the W‐Mo‐Cu skarn deposits in the Eastern Segment of the Jiangnan Uplift Metallogenic Belt (ESJUB). The magmatic and metallogenic materials mainly came from the Neoproterozoic basement, with the possible participation of a small amount of mantle components. The late stage magmatism was dominated by volcanic rocks with a small amount of intrusive rocks, which were consistent with the limited volcanic‐intrusive activities in the second stage of the MLYB. The H‐O stable isotopes of ore deposits in the region indicate that the ore‐forming hydrothermal fluids of the porphyry and skarn deposits were mostly of magmatic water for the ore‐forming stage, the percentage of meteoric water obviously increasing during the late ore‐forming stage. The ore‐forming materials of the deposits are mainly from the deep magma with a few sedimentary wall rocks, according to the stable carbon isotopes of the carbonates in the ore deposits. Additionally, according to previous research, the molybdenite from the MLYB has a higher Re content than that of the ESJUB. The higher content of Re in the molybdenite from the Shizishan deposit is identical to that of MLYB rather than ESJUB, whereas Re characteristics in molybdenite of Magushan deposit are similar to that of ESJUB. The differences in Re characteristics indicate the different deep processes and ore‐forming material sources (mainly mantle composition for the former and crustal materials for the latter) of these ore deposits on opposite sides of the JDF.

3D mineral exploration targeting with multi-dimensional geoscience datasets, Tongling Cu(-Au) District, China

The Tongling Cu(-Au) district is the most important magma-skarn type Cu(-Au) polymetallic districts in the Middle-Lower Yangtze metallogenic belt of China. The previous studies in the Tongling Cu(Au) district compiled available digital geological, geochemical, geophysical, and remote sensing datasets. As the discovery of near-surface Cu(-Au) deposits becomes more and more difficult in the Tongling Cu(-Au) district, we face the challenge of exploring for blind mineral deposits in the subsurface. Three-dimensional (3D) mineral potential mapping can provide effective exploration targeting by integrating multi-source and multi-dimension geoscience datasets. In this paper, firstly, a 3D district-scale geological model was constructed from multiple geoscience datasets. Secondly, multi-level (0 m, −300 m, −600 m, −900 m, −1200 m) exploration criteria were extracted by spatial analyses. Thirdly, the weights-of-evidence method, discrete smooth interpolation, and ordinary kriging interpolation were used to integrate multi-level exploration criteria including two-dimensional (2D) surface geochemical and remote sensing data into a 3D posterior-probability model. Finally, the concentration-area and concentration-volume fractal methods were used to define posterior-probability thresholds to outline 2D and 3D targets, respectively. The results indicated that the integrating performance of ordinary kriging interpolation is better than that of discrete smooth interpolation in 3D posterior-probability modeling. The whole procedure yielded a series of high-potential Cu(-Au) targets. The methodology discussed here can be used in other magma-skarn districts in the world.

Microfabrics, in-situ trace element and sulfur isotope compositions of pyrite from the Jinjiwo copper deposit in Chengmenshan orefield, northern Yangtze Block: Syngenetic stratabound mineralization and hydrothermal remobilization

The Jinjiwo copper deposit is located in the Jiurui ore district of the Middle-Lower Yangtze Metallogenic Belt. The deposit has stratiform orebodies hosted by Late Carboniferous carbonate units. Pyrite is the dominant metallic mineral in the ores. Here we report on an integrated study on the microfabrics, Raman spectroscopy, in-situ LA-(MC-)ICP-MS trace element and sulfur isotope of pyrite, with a view to understand the geochemical variation, genesis of copper mineralization and ore-forming process. Textural observations suggested four types of pyrite corresponding to three metallogenic episodes: syngenetic sedimentation (PyI), metamorphism or deformation (PyII), and skarn-hydrothermal mineralization including the late skarn stage (PyIII) and hydrothermal stage (PyIV). Raman spectra of pyrite reveal subtle differences in band position and widths (FWHM) and display the increasing formation temperature of from PyI, through PyIV and PyIII, to PyII. Colloform and laminated pyrite (PyI) share similarities in behavior of pairs of elements and have low Co/Ni ratios, and the former contains the highest concentrations of Bi, Cu, Pb, Zn, Ag, Au, Mn that suggest rapid precipitation from highly saturated fluids. PyII shows high Co, Ni and As concentrations and Co/Ni ratios of 0.03 to 6.19. PyIII and PyIV have greatly varying Co/Ni ratios of 1.07 to 29 and typically low Au concentrations, suggesting a hydrothermal source. PyIII is rich in Co and Se, but is depleted in As, Cu, Pb, Zn, Ag, and Au in comparison with PyIV. There are two kinds of sulfur: one is that δ34S values are near zero, suggesting that the pyrite sulfur in the ores was derived from a mixed source in deep crust, and the other is that δ34S values are less than −39.1‰, indicating the sedimentary pyrite sulfur was originated from bacterial sulfate reduction. The combined textural and compositional data of pyrite suggest that the formation of the Jinjiwo copper deposit might have recorded the submarine exhalation sedimentation and the Mesozoic tectonic transition-deformation and hydrothermal overprint.

Geological and geochemical characteristics and genesis of the Cishan gold deposit in Tongling ore cluster area, Anhui Province

The Cishan gold deposit is a newly discovered medium-scale independent skarn gold deposit located in the Tongling ore cluster area of the Middle-Lower Yangtze Metallogenic Belt, and the ore-related intrusion is the Cishan pyroxene diorite. In this study, we investigated the zircon U–Pb Geochronology, whole-rock geochemistry of the Cishan ore-related pyroxene diorite, and C–O–S isotope compositions of hydrothermal calcites and metal sulfides in the ores. The pyroxene diorite was emplaced at ca. 141.7 ± 0.36 Ma. They are metaluminous and record high-K calc alkaline and shoshonite series with the characteristics of high Al and alkali (K, Na), enriched in LREEs and LILEs (Rb, K, Ba, Sr), depleted in HREEs and HFSEs (Th, U), without significant Eu anomalies. We suggest that the magma of the Cishan pyroxene diorite was probably derived from partial melting of the enriched lithospheric mantle mixed with a small amount of crustal derived melts, and then underwent crystallization differentiation and weakly upper crustal contamination during the magmatic ascending. The δ13CV-PDB and δ18OV-SMOW values of the hydrothermal calcites range from −5.1‰ to −0.5‰ and 11.7‰ to 16.2‰ respectively, and the δ34SV-CDT values of sulfide ore minerals range from −0.7‰ to 6.0‰, showing that the ore-forming fluids and materials were derived from the magma. Combined with previous studies, we proposed that both the Cishan intrusion and skarn gold deposit were formed under the tectonic transition period from compressional to extensional setting, and the Middle–Lower Yangtze Metallogenic Belt was located in the inland side of the continental margin arc under the subduction of the paleo-Pacific plate.

Constraints on the Genesis of the Qixiashan Pb-Zn Deposit, Nanjing: Evidence from Sulfide Trace Element Geochemistry

The large-scale Qixiashan Pb-Zn Deposit in the eastern Middle-Lower Yangtze metallogenic belt is hosted in carbonate rocks. Based on a detailed mineral paragenesis study, in-situ LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometer) trace element geochemistry data for pyrite and sphalerite from different stages in the Qixiashan Deposit are reported, the Pb-Zn mineralization processes are reconstructed, and a genetic model is constructed. Four paragenetic stages of Pb-Zn ore deposition are identified: the biogenic pyrite mineralization stage (Stage 1), the early stage of hydrothermal Pb-Zn mineralization (Stage 2), the late stage of hydrothermal Pb-Zn mineralization (Stage 3), and the carbonate stage (Stage 4). Stages 2 and 3 are the main ore stages. The trace element characteristics of the sulfide in stages 2 and 3, such as the higher Co/Ni and lower trace element contents of the pyrite and the Fe, Mn, and Ge contents of the sphalerite, indicate that they were generated by magmatic-hydrothermal processes. Furthermore, the lower Cu, Ag, Sb, and Pb contents of the pyrite and sphalerite of Stage 3 compared to Stage 2 suggest an increase in magmatic-hydrothermal activity from Stage 2 to Stage 3. The hydrothermal fluids leached trace elements (e.g., Cu, Ag, Sb, and Pb) from the previously deposited primary pyrite and sphalerite, which were precipitated in the later hydrothermal stage Cu, Au, Ag, Sb, and Pb bearing minerals and secondary pyrite and sphalerite with lower trace element contents (e.g., Cu, Au, Ag, Sb, and Pb). Compared with the pyrite from stages 2 and 3, the Stage 1 pyrite has relatively higher trace elements contents (Sb, Cu, Zn, Au, Ag, Pb, As, and Ni). However, their lower Co/Ni ratio suggests a syngenetic sedimentary origin. Based on the petrographic features and trace element data, a multi-stage mineralization model is proposed. The Stage 1 biogenic pyrite formed stratiform pyrite layers, which provided reducing conditions and a base for the subsequent Pb-Zn mineralization. During Stage 2, subsequent hydrothermal fluid interacted with the stratiform pyrite layers, which resulted in sulfide precipitation and the formation of stratiform Pb-Zn orebodies. In Stage 3, the hydrothermal fluid replaced the limestone along the fractures, which triggered the formation of Pb-Zn vein orebodies.

Zircon geochemistry of Edong granitoids in the Middle-Lower Yangtze Metallogenic Belt (Eastern China): Constraints on W-Cu-Fe skarn mineralization

It has long been established that skarn deposits of different metals are associated with intrusions of different compositions. Intermediate-felsic granitoids in the Edong district of the Middle-Lower Yangtze Metallogenic Belt host skarn deposits with varying W-Cu-Fe proportions, yet previous whole-rock geochemical studies could not distinguish between the magmatic suites that formed the different skarn deposits. In this study, LA-ICP-MS zircon geochemical data are presented for the Ruanjiawan W skarn (60300 t WO3), Tongshankou Cu skarn (0.6 Mt Cu), Tonglushan Cu-Fe skarn (1.1 Mt Cu and 56.8 Mt Fe) and Jinshandian Fe skarn (200 Mt Fe) deposits in the Edong district. Zircons from the ore-forming intrusions of these skarn deposits are all characterized by heavy rare earth element (HREE) enrichments and light rare earth element (LREE) depletions, with positive Ce anomalies and slightly negative Eu anomalies. Tungsten contents in zircons from the W ore-forming intrusion (0.02–3.16 ppm W; avg. 1.14 ppm) are generally higher than in zircons from the Cu ore-forming intrusion (0.00–0.24 ppm W; avg. 0.03 ppm). Copper content in zircons from the Cu ore-forming intrusion is higher than in those from the W ore-forming intrusion. Fertile intrusive rocks from the four skarn deposits contain zircons with high calculated Ce4+/Ce3+ ratios (Ruanjiawan: 71.7; Tongshankou: 207.5; Tonglushan: 263.6; Jinshandian: 189.0. Fluorine content of the Ruanjiawan intrusion is higher than the Tonglushan and Jinshandian intrusions, followed by the Tongshankou intrusion. Chlorine contents show the opposite trend. We propose that the different source regions for the ore-fertile intrusions is the critical factor that controls the metal content, oxygen fugacity and volatile components. Our studies suggest that zircon geochemistry is a good indicator to distinguish tungsten causative intrusions from copper- and iron ore related intrusions (i.e. W content ≧ 1.14 ppm and Ce4+/Ce3+ ratios ≦ 207.5).

Breccia, hydrothermal alteration and structural geology of the Huangtun porphyry Au-Cu deposit in the Middle-Lower Yangtze Metallogenic Belt, eastern China

Luzong Basin is an important part of the Middle-Lower Yangtze Metallogenic Belt in eastern China, in which the dominant types of deposits are iron-oxide-apatite and skarn iron deposits. However, a new porphyry gold-copper deposit, Huangtun deposit, has recently been discovered in the north-eastern margin of the basin. Detailed studies of geological characteristics and metallogenic processes of Huangtun gold-copper deposit are needed to supplement the mineralisation type of the Luzong Basin. Based on drill core logging and petrology observations of thin sections and polished sections, a north-striking sinistrial strike-slip major fault and a series of secondary NE-striking sinistrial strike-slip faults have been identified in the mining area. A mineralised breccia pipe at the intersection of the two groups of faults is the main host of the Au ore body. The alteration types in the mining area, from deep to shallow, include an albite alteration zone, a biotite-albite alteration zone, a chlorite alteration zone and a sericite-pyrite alteration zone. A detailed mapping of the breccia pipe has been provided in the mining area. Seven different breccias facies have been divided according to the internal structure, composition, morphology, matrix content and alteration assemblages. Genesis of the different breccia facies have been identified based on crosscutting relationships and clast-in-clast textures, which revealed that there are two different faulting and brecciation stages. During the first stage, matrix-supported breccia formed near the fracture zone. Gold-copper mineralisation then occurred along the intersection of the two groups of fracture zones, which formed K-Na silicate to sericite altered magmatic-hydrothermal breccia, from deep to shallow. In addition, these different facies of breccia correspond to four stages of fluid evolution: the albite stage, biotite-albite stage, chlorite stage and sericite-pyrite stage. Hydrothermal breccia with a high matrix/cement ratio then formed when mineralizing fluid permeated the fracture zone. During the second stage, the ore bodies were faulted to form tectonic breccia containing some massive carbonate ± quartz ± pyrite clusters as clasts. Based on the current study, we conclude that the locations of the intersection of fault zones in the northern part of the Luzong Basin and the northern part of the mining area have potential for further gold mineralisation.

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

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

Geochemical characteristics of magnetite in Longqiao skarn iron deposit in the Middle-Lower Yangtze Metallogenic Belt, Eastern China

The Longqiao Fe deposit is the only large stratabound Fe skarn in Eastern China. This extensive ore body is suitable for investigating the spatial variations in trace elements in magnetite from the intrusion to the wall rocks and tracing the evolution of the mineralizing fluid in a skarn deposit. Magnetite samples were collected every 200 m from the ore-forming gabbro-diorite to the edge of the ore body, including the diopside-magnetite and epidote-chlorite-magnetite stages. Our results show that magnetite proximal to the gabbro-diorite displays lower Mg, Al, and Si and higher contents of Ti and V than those found further from the gabbro-diorite. The hydrothermal fluids in both diopside-magnetite and epidote-chlorite-magnetite stages were influenced by reaction with marine sedimentary rocks. Magnetites from different parts of the ore body display a wide range of trace element contents and fall into the porphyry and skarn fields on a (Mn + Al) vs. (Ti + V) discrimination diagram. Based on our results and published data, we propose that the early-stage magnetite from skarn and iron oxide-apatite (IOA) Fe deposits is compositionally similar, and fluid compositional variations are largely dependent on differences in the composition of the wall rock and the intensity of fluid-rock interactions. This results in a large variation in (Ti + V) in magnetite compositions from skarn deposits in the (Mn + Al) vs. (Ti + V) discrimination diagram, which is different from IOA deposits. This study shows that magnetite trace element evolution trends can provide a reliable indication to recognize skarn and IOA deposit types.