Middle Lower Yangtze River Research Articles

A genetic link between iron oxide-apatite and iron skarn mineralization in the Jinniu volcanic basin, Daye district, eastern China: Evidence from magnetite geochemistry and multi-mineral U-Pb geochronology

Abstract Various styles of ore deposits may form from a single magmatic-hydrothermal system. Identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic-hydrothermal processes, but can also help in successful mineral exploration. Both iron oxide-apatite (IOA) and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition, but whether these two ore types can form from the same magmatic intrusion remains poorly understood. In this study, we present a comparative study between a newly identified subsurface IOA ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the Jinniu volcanic basin of the Daye district, Middle-Lower Yangtze River metallogenetic belt (MLYRMB), eastern China in order to highlight a genetic link between these two styles of mineralization. The IOA ores are dominated by Ti-rich magnetite with variable amounts of fluorapatite, diopside, and actinolite. This mineralogical assemblage is distinctly different from the iron skarn ores, which consist mainly of Ti-depleted magnetite and subordinate pre-ore garnet and diopside, and post-ore quartz, chlorite, calcite, and pyrite. In addition, magnetite from the IOA ores is characterized by well-developed ilmenite lamellae and has high concentrations of Ni, V, Co, and Ga, consistent with high temperature crystallization, whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower Ni, V, Co, and Ga, indicating their formation under relatively low temperatures. Titanite and fluorapatite from the IOA ores have U-Pb ages of 132.5 ± 2.4 Ma to 128.4 ± 3.0 Ma, which match a titanite U-Pb age for the associated iron skarn ores (132.3 ± 2.0 Ma), and are consistent with zircon U-Pb ages for the ore-hosting diorite porphyry (130.4 ± 0.7 Ma to 130.3 ± 0.5 Ma). This age consistency supports a possible genetic link among the diorite porphyry, IOA ores, and iron skarn ores. We propose that the IOA and skarn ores are the products of two consecutive mineralization stages of the same magmatic-hydrothermal system, involving a high-temperature, hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature, diluted hydrothermal fluid. Other IOA and iron skarn deposits of similar ages (130 Ma) are found in a series of volcanic basins in the MLYRMB, which forms one of the world’s largest IOA metallogenic belts. The close association of the two ore styles identified at Daye provides a useful exploration guide for IOA and iron skarn deposits both on a local and regional scale.

Fluid evolution of the Wushan skarn-dominant copper deposit in the Middle-Lower Yangtze River metallogenic belt, Eastern China

The Wushan copper skarn deposit (1.37 Mt at 1.17% Cu) is located in the Middle-Lower Yangtze River polymetallic belt. Skarn orebodies mainly occur in the Carboniferous and Permian carbonates adjacent to Early Cretaceous granodiorite porphyries (148–138 Ma). Ore deposition underwent two episodes of metallogenic events, involving hydrothermal evolution followed by skarn formation and porphyry-related mineralization. The skarn episode formed massive, disseminated, veinlet- and breccia-style mineralization at the contact zone, whereas porphyry mineralization is characterized as disseminated and veinlet-style only. Various types of fluid inclusions (daughter mineral-bearing, CO2-bearing, vapor and aqueous–vapor) are classified based on their fluid composition and phase assemblages.The hydrothermal fluids are mainly derived from a magmatic origin, which exsolves during the melt-fluid differentiation. Primary fluid in endoskarn is interpreted as representing two immiscible phases evolving from a low-salinity initial fluid. The initial supersaturated fluid has a relative low salinity and the wide range of Th values (433–626 °C) implies heterogeneous trapping, corresponding to pressures of 371–646 bars and hydrostatic depth of 3.7–6.5 km. Primary fluid inclusions trapped in syn-ore quartz show the coexistence of S-type inclusions (~30.0 wt% NaCl equiv) with vapor-rich and liquid-rich inclusions, indicating fluid immiscibility and phase separation from heterogeneous trapping. The homogenization temperatures (347–434 °C) of primary vapor-rich inclusions represent the trapping temperatures, corresponding the trapped pressures range from 152 to 374 bars and a hydrostatic depth of 1.5–3.7 km. Copper mineralization in episode porphyry occurs on a very small scale and have a clear trend of decreasing temperatures and salinities during fluid evolution. A similar scenario occurred during the porphyry episode in which fluid immiscibility led to copper mineralization.Significant trends of decreasing temperatures and salinities for both mineralization episodes reflect the change from a magmatic fluid-dominated system to a mixed source fluid that incorporated formation water from the country rocks and/or meteoric water. Controlled by the chemical transition of the fluid, this mixing process produced a relatively cool fluid system with lower salinities, which enhanced the precipitation of Cu–Fe sulfides. H–O–C isotope signatures further indicate that both the fluid and metal are predominantly derived from magmatic sources, and that multiple fluid pulses contributed to form skarn minerals and sulfides in the Wushan deposit.

Increasing Outbreak of Cyanobacterial Blooms in Large Lakes and Reservoirs under Pressures from Climate Change and Anthropogenic Interferences in the Middle–Lower Yangtze River Basin

In recent decades, the increasing frequency and severity of cyanobacterial blooms in recreational lakes and water supply reservoirs have become a great concern to public health and a significant threat to the environment. Cyanobacterial bloom monitoring is the basis of early warning and treatment. Previous research efforts have always focused on monitoring blooms in a few specific lakes in China using moderate resolution imaging spectroradiometer (MODIS) images, which are available for the years 2000 onward. However, the lack of overall information on long-term cyanobacterial blooms in the lakes and reservoirs in the middle–lower Yangtze River (MLYR) basin is an obstacle to better understanding the dynamics of cyanobacterial blooms at a watershed scale. In this study, we extracted the yearly coverage area and frequency of cyanobacterial blooms that occurred from 1990 to 2016 in 30 large lakes and 10 reservoirs (inundation area >50 km2) by using time series Landsat satellite images from Google Earth Engine (GEE). Then, we calculated the cyanobacterial bloom area percentage (CAP) and the cyanobacterial bloom frequency index (CFI) and analyzed their inter-annual variation and trends. We also investigated the main driving forces of changes in the CAP and CFI in each lake and reservoir. We found that all reservoirs and more than 60% of lakes exhibited an increasing frequency and coverage area of cyanobacterial blooms under the pressures of climate change and anthropogenic interferences. Reservoirs were more prone to be affected by fertilizer consumption from their regional surroundings than lakes. High temperatures increased blooms of cyanobacteria, while precipitation in the lake and reservoir regions somewhat alleviated blooms. This study completes the data records of cyanobacterial blooms in large lakes and reservoirs located in hotspots of the MLYR basin and provides more baseline information before 2000, which will present references for water resource management and freshwater conservation.

In-situ major and trace element chemistry of melanite from Tieshan Fe–Cu skarn deposit, Hubei Province, Eastern China: Implications for hydrothermal fluid evolution

The Tieshan Fe–Cu skarn deposit is located in the Edong ore district, the largest ore district of the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in Eastern China. The Fe–Cu mineralization is spatially associated with the Tieshan pluton, which intruded the carbonates of the Lower Triassic Daye Formation. The orebodies are predominantly hosted along the intrusive contact zone between the (quartz)-diorite and (dolomitic)-marble. EMPA analysis shows that the Tieshan garnets belong to high-Ti andradite, with TiO2 contents ranging from 0.03 to 2.59 wt%, and is designated as melanite. The melanite contains low Na content, suggesting the absence of Na+-REE3+ coupled substitution. LA–ICP–MS analysis shows high total LREE (∑LREE), low ∑HREE and positive Eu anomalies, suggesting high fO2 and rapid growth of the melanite. Compared with other Ti-rich garnets worldwide, the Tieshan melanite grains are more Al-rich and Si-rich, and shows negative SiO2 vs. TiO2 correlation, which suggests predominant Ti-substitution in the tetrahedral site. The more positive Eu anomalies and higher percentage of andradite are present in the rim (than in the core), indicating lower salinities and higher fO2 of the late-stage ore-forming fluid. The magmatic-hydrothermal fluid source of these garnets supports the metasomatic ore genesis at Tieshan.

Assessing the efficiency and sustainability of wheat production systems in different climate zones in China using emergy analysis

China is the country with the largest wheat planting area in the world, and wheat is one of the two main staple food crops consumed in China. Wheat is widely cultivated in 15 provinces throughout the country and across 3 climate zones including the subtropical monsoon climate zone, temperate monsoon climate zone and temperate continental climate zone. The natural conditions of each climate zone are different, and the ways in which the wheat production system operates are different. To ultimately safeguard the production and explore the similarities and differences in input and output of the same system under different climate conditions, the emergy method was used to research the comprehensive performance of the wheat production system based on 2014 statistical data from China. The results indicate that there was a significant variance in the input of local renewable environmental resources, ranging from 0.48E+14 sej/ha in Xinjiang in the temperate continental climate zone to 4.46E+14 sej/ha in Shaanxi in the temperate monsoon climate zone. Among the three climatic zones, the temperate continental climate zone had the lowest emergy self-support ratio (0.13), followed by the temperate monsoon climate zone (0.15) and then the subtropical monsoon climate zone (0.20). Regions in which natural resources are insufficient, such as temperate continental climate zone, need additional purchased resources to maintain normal operation of the wheat production system. Compared with other intensive agricultural production systems, the wheat production system is extensive and low-cost and has room for improvement with more artificial input. The Middle-Lower Yangtze River Plain at the junction of temperate monsoon climate zone and subtropical monsoon climate zone is the most efficient region for planting wheat based on the ratio of the entire emergy input to the entire energy output. This ratio should be considered in the adjustment of the agricultural cropping structure to make use of resources more effectively.

High-resolution 3D crustal S-wave velocity structure of the Middle-Lower Yangtze River Metallogenic Belt and implications for its deep geodynamic setting

The Middle-Lower Yangtze River Metallogenic Belt (MLYMB) is an important mineral resource region in China. High-resolution crustal models can provide crucial constraints to understand the ore-forming processes and geodynamic setting in this region. Using ambient seismic noise from 107 permanent and 82 portable stations in the MLYMB and the adjacent area, we present a new high-resolution 3D S-wave velocity model of this region. We first extract 5–50 s Rayleigh wave phase velocity dispersion data by calculating ambient noise cross-correlation functions (CFs) and then use the surface wave direct inversion method to invert the mixed path travel times for the 3D S-wave velocity structure. Checkerboard tests show that the horizontal resolution of the 3D S-wave velocity model is approximately 0.5°–1.0° and that the vertical resolution decreases with increasing noise and depth. Our high-resolution 3D S-wave velocity model reveals: (1) A V-shaped high-velocity zone (HVZ) is located in the lower crust and the uppermost mantle in the study region. The western branch of the HVZ passes through the Jianghan Basin, the Qinling-Dabie orogenic belt and the Nanxiang Basin. The eastern branch, which almost completely covers the main body of the MLYMB, is located near the Tanlu Fault. The low-velocity anomalies between the western and eastern branches are located in the area of the Qinling-Dabie orogenic belt. (2) High-velocity uplifts (HVUs) are common in the crust of the MLYMB, especially in the areas near the Tanlu Fault, the Changjiang Fault and the Yangxin-Changzhou Fault. The intensities of the HVUs gradually weaken from west to east. The V-shaped HVZ in the lower crust and uppermost mantle and the HVUs in the middle and lower crust likely represent cooled mantle intrusive rocks. During the Yanshanian period, fault systems formed in the MLYMB due to the convergence between the South China Plate and the North China Plate, the multiple-direction drifting of the Paleo-Pacific Plate and its subduction beneath the Eurasian Plate. The dehydration of the cold oceanic crust led to partial melting in the upper mantle. Temperature differences caused strong convection of the upper mantle material that underplated the lower crust and rose to near the surface along the deep fault systems. After mixing with the crustal materials, mineralization processes, such as assimilation and fractional crystallization, occurred in the MLYMB.

Texture and trace element geochemistry of quartz in skarn system: Perspective from Jiguanzui Cu–Au skarn deposit, Eastern China

The Jiguanzui Cu–Au deposit is an important skarn deposit in the Edong ore district of the Middle–Lower Yangtze River Valley Metallogenic Belt (MLYRB), Eastern China. The skarn mineralization occurs dominantly in the intrusive contact between quartz diorite and marble of the Lower-Middle Triassic Jialingjiang Formation. The main mineralization stage (quartz-sericite-pyrite-chalcopyrite) is characterized by abundant quartz, which can be grouped as quartz in orebodies (Qtz1), quartz in quartz-pyrite hydrothermal veins in hornfels of the Middle Triassic Puqi Formation and quartz diorite (Qtz2 and Qtz3, respectively). Cathodoluminescent (CL) imaging reveals core-rim texture in Qtz1 and oscillatory zoning in Qtz2 and Qtz3, suggesting that Qtz1 was formed under low crystallization rate, in a relatively stable closed system, whereas Qtz2 and Qtz3 were formed under high crystallization rate, in an open system with oscillatory physicochemical fluctuations. As the main trace element in the Jiguanzui quartz, aluminum is incorporated into quartz as trivalent Al3+ to substitute Si4+. Monovalent alkali metal (esp. Li+) and divalent cations (Ge2+, Sr2+) act as charge compensators for the Al3+ substitution. Titanium concentrations (mostly <10 ppm) and the clear positive Al vs. Li correlation indicate the main mineralization at Jiguanzui formed under low temperature (<350 °C). Additionally, CL reflectivity of Qtz1 increases from core to rim, suggesting neutralization of the acidic ore fluids, which is interpreted to be an important cause of metal sulfide precipitation at Jiguanzui.

In situ LA–ICP–MS trace element analyses of magnetite: genetic implications for the Zhonggu orefield, Ningwu volcanic basin, Anhui Province, China

The Zhonggu orefield is located within the southern Ningwu volcanic basin and is one of the largest iron ore districts within the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) of eastern China. The area hosts the Gushan iron oxide–apatite (IOA) deposit and the Baixiangshan, Longshan, Hemushan, Zhongjiu, and Taipingshan skarn-type iron deposits. Here, we employ laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) to determine trace element concentrations in magnetite from these deposits. Combining these new data with geological information from these deposits indicates that the iron ore within the Gushan deposit has V and Ti compositions that are strongly suggestive of a Kiruna-type IOA origin. Specifically, the V and Ti chemistry of magnetite in iron ore breccias from the Gushan deposit suggests that this style of mineralization formed at a high temperature and as a result of magmatic magnetite precipitation. This was followed by precipitation of lower temperature magmatic–hydrothermal massive magnetite. Both types of magnetite host exsolved ilmenite. Elemental mapping also indicates that Gushan breccia-hosted magnetite records hydrothermal fluid activity that formed late-stage vein mineralization. In comparison, other deposits within the Zhonggu orefield all contain magnetite with compositions that are indicative of skarn mineralization. This implies that these deposits formed as a result of magmatic–hydrothermal rather than purely magmatic or purely hydrothermal activity, contrasting with the Gushan deposit. Finally, the geochemistry of magnetite within thick anhydrite units in the Longshan deposit indicates the formation by low-temperature sedimentary processes, and this magnetite was subsequently overprinted as a result of hydrothermal activity during the formation of the main Longshan deposit. Overall, this study indicates that the IOA, skarn-type, and sedimentary anhydrite-type iron mineralization in the Zhonggu iron ore field record evolving metallogenic processes from initially orthomagmatic mineralizing systems to high- to moderate-temperature magmatic–hydrothermal systems and finally to low-temperature hydrothermal mineralization.

Geochronology and geochemistry of the five magmatic rocks in the Ningzhen region, China

The Ningzhen region of China is located in the easternmost part of the middle-lower Yangtze River Cu–Fe polymetallic metallogenic belt. From west to east, it comprises five main intermediate–acidic intrusive complexes: the Qilinmen, Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes. Geochemical investigations show that these five intrusive complexes exhibit high contents of SiO2, at 64.74–73.40 wt%, Al2O3, at 14.15–17.37 wt%, and K2O + Na2O, at 6.49–8.68 wt%. The majority of the samples belong to the high-K calc-alkaline series, with a few samples plotting in the calc-alkaline and tholeiitic series. Trace element analysis shows that the samples are enriched in large ion lithophile elements (LILE) and are depleted in high field strength elements (HFSE). The chondrite-normalized rare earth element (REE) patterns are characterized by right-inclined curves, showing light rare earth element (LREE) enrichment. In addition, the (La/Yb)N ratios are high at 15.02–37.28, with an average of 29.13, and slightly negative or none Eu anomalies are present. In the (La/Yb)N–δEu diagram, the samples plot within the crust-mantle type field. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb dating yielded ages of 122.0 ± 1.0 Ma, 106.1 ± 0.8 Ma, 108.7 ± 1.4 Ma, 103.5 ± 1.9 Ma, and 96.8 ± 1.7 Ma for the Qilinmen, Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes, respectively. On the basis of this research and knowledge of several known metal deposits related to these complexes, we suggest that the Mesozoic large-scale diagenesis and metallogenesis in the Ningzhen region may have ceased at 100 Ma or about 95 Ma.

Genetic Types and Metallogenic Model for the Polymetallic Copper–Gold Deposits in the Tongling Ore District, Anhui Province, Eastern China

AbstractThe Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered (from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn‐ or porphyry–skarn‐type deposits; however there have been recent discoveries of numerous vein‐type Au, Ag, and Pb‐Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore‐controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits (skarn‐, porphyry‐, and vein‐type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore‐forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry‐, skarn‐, and vein‐type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep‐seated and concealed porphyry‐type Cu (–Mo, –Au) deposits as well as shallow vein‐type Au, Ag, and Pb–Zn deposits in this area and elsewhere.

Distal Au Deposits Associated with Cu-Au Skarn Mineralization in the Fengshan Area, Eastern China

Research Article| February 01, 2019 Distal Au Deposits Associated with Cu-Au Skarn Mineralization in the Fengshan Area, Eastern China Guiqing Xie; Guiqing Xie 1Ministry of Natural Resources (MNR) Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China2Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada †Corresponding author: e-mail, xieguiqing@cags.ac.cn Search for other works by this author on: GSW Google Scholar Jingwen Mao; Jingwen Mao 1Ministry of Natural Resources (MNR) Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China Search for other works by this author on: GSW Google Scholar Jeremy P. Richards; Jeremy P. Richards 2Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Search for other works by this author on: GSW Google Scholar Yingxiao Han; Yingxiao Han 3School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China Search for other works by this author on: GSW Google Scholar Bin Fu Bin Fu 4Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Guiqing Xie 1Ministry of Natural Resources (MNR) Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China2Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Jingwen Mao 1Ministry of Natural Resources (MNR) Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences (CAGS), Beijing 100037, China Jeremy P. Richards 2Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Yingxiao Han 3School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China Bin Fu 4Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia †Corresponding author: e-mail, xieguiqing@cags.ac.cn ☼Current address: Institute of Mineral Resources, Chinese Academy of Geological Sciences, No. 26 Baiwanzhuang Road, Beijing 100037, China. Publisher: Society of Economic Geologists Accepted: 23 Nov 2018 First Online: 28 Feb 2019 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2019 Economic GeologyEconomic Geology Economic Geology (2019) 114 (1): 127–142. https://doi.org/10.5382/econgeo.2019.4623 Article history Accepted: 23 Nov 2018 First Online: 28 Feb 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Guiqing Xie, Jingwen Mao, Jeremy P. Richards, Yingxiao Han, Bin Fu; Distal Au Deposits Associated with Cu-Au Skarn Mineralization in the Fengshan Area, Eastern China. Economic Geology 2019;; 114 (1): 127–142. doi: https://doi.org/10.5382/econgeo.2019.4623 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Carbonate-hosted Au deposits (12 million tonnes at 5.0 g/t Au) are located less than 1.5 km away from Cu-Au skarn deposits in the Fengshan area, Middle-Lower Yangtze River metallogenic belt, eastern China. The skarn deposits occur in the contact zones of late Mesozoic granodiorite porphyry intrusions. Bismuth tellurides and coloradoite (HgTe) occur in Cu-Au skarn and peripheral Au-As ores, respectively, whereas tellurides, including coloradoite, and lorandite (TlAsS2) are present in carbonate-hosted Au ores outside the marble front. New zircon U-Pb ages indicate that the granodiorite porphyry intrusions spatially related to both Cu-Au skarn and carbonate-hosted Au deposits were emplaced between 149.9 ± 1.3 and 145.9 ± 0.7 Ma, which overlaps with molybdenite Re-Os ages of 149.1 ± 2.1 to 145.4 ± 2.9 Ma from the Cu-Au skarn deposits. Sulfur isotope compositions of sulfide minerals from the Cu-Au skarn deposits (δ34S = –2.5 to 6.4‰) are similar to those from carbonate-hosted Au deposits (δ34S = –4.8 to 2.6‰), suggesting a similar magmatic source of sulfur. Geologic, mineralogical, and sulfur isotope evidence collectively indicate that the carbonate-hosted Au deposits are the distal product of Cu-Au skarn mineralization rather than Carlin-type Au deposits, as has been previously suggested. This study proposes a genetic model to illustrate possible linkages between oxidized Cu-Au skarn deposits (associated with oxidized magmas) and carbonate-hosted Au deposits, which may have important implications for Au deposits in the more distal parts of Cu-Au skarn systems in the Middle-Lower Yangtze River metallogenic belt and elsewhere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Short wavelength infra-red (SWIR) characteristics of hydrothermal alteration minerals in skarn deposits: Example from the Jiguanzui Cu–Au deposit, Eastern China

The Jiguanzui Cu–Au deposit is an important skarn deposit in the Edong ore district of the Middle–Lower Yangtze River Valley metallogenic belt (MLYRB, Eastern China). The mineralization occurred dominantly in the Lower-Middle Triassic Jialingjiang Formation marble, either along interlayer fracture zones or along the intrusive contact with the Early Cretaceous quartz diorite. Based on the mineral assemblages and textural relationships, the Jiguanzui alteration/mineralization can be divided into five stages, namely (I) prograde skarn alteration (garnet-pyroxene), (II) retrograde alteration (hornblende-epidote-actinolite), (III) hematite mineralization, (IV) quartz-sericite-pyrite-chalcopyrite mineralization (main Cu-Au mineralization stage) and (V) calcite-sulfide mineralization (pyrite-chalcopyrite-molybdenite-galena-sphalerite).Systematic short wavelength infrared (SWIR) spectral analyses show that alteration minerals at Jiguanzui include mainly sericite group minerals (montmorillonite, illite and muscovite), kaolinite, and carbonate minerals (calcite, ankerite and dolomite), with minor chlorite, halloysite and dickite. Spectral features of Stage IV sericite group minerals indicate that the Al-OH absorption feature wavelength positions (Pos2200) have shifted toward longer wavelengths (>2209 nm) in the ore proximal area, which may be caused by the substitution of Fe and Mg in the octahedral Al site. The vertical distance of mineralization indication can reach up to ca. 450 m, but can be affected by the wall-rock lithology and the Jiguanshan fault zone. The Fe-OH absorption feature wavelength positions (Pos2250) of chlorite in the Middle Triassic Puqi Formation hornfels have also shifted toward longer wavelengths in the ore proximal area, which may be caused by the relative Mg-rich nature of the chlorite. We conclude that the high Pos2200 (>2209 nm) of sericite group minerals and the high Pos2250 of chlorite can be used as prospecting tools for the Jiguanzui Cu–Au skarn mineralization.

Genesis of Chating Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China: Implications from magnetite and biotite geochemistry

Porphyry deposits developed in intracontinental settings have some geological characteristics that differ from those developed in arc-related continental margins. The Chating deposit is a newly discovered Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt (MLYB), eastern China. We carried out detailed petrographic observations and major and trace element analyses of different types of magnetite and biotite from the host quartz diorite porphyry and different alteration zones in Chating to elucidate the genesis of Chating deposit.Alteration types in Chating include skarn, sodic-calcic, potassic and phyllic, and copper mineralization is closely associated with potassic alteration of quartz diorite porphyry. The different types of magnetite and biotite at Chating show distinctive geochemical characteristics. Higher Ti and Al in magmatic magnetites and biotites compared to the hydrothermal minerals indicate higher temperature and pressure in the quartz diorite porphyry. Higher V in magmatic magnetites and lower XMg in magmatic biotites indicate higher fO2. Similar mineral geochemistry from typical worldwide porphyry deposits, for example, Al2O3, TiO2, FeOT, MgO, Na2O, IV(F) and IV(Cl) contents in biotite, and Ni/Cr, Ti, Al, Sn and Ga in magnetite, indicate a predominately magmatic fluid source. Differences in Si, Ca, Co/Ni, Mg, and Mn in different types of magnetite, and MnO, CaO, SiO2 differences in two types of biotite from typical porphyry copper deposits show the influence of external fluids. Moreover, high IV(F) values and low IV(Cl) values in biotites demonstrate that the magmatic-hydrothermal system in Chating was enriched in Cl and lacked F, consistent with the importance of Cl in the transport of Cu. Based on different discrimination diagrams for magnetite, such as Ni/Cr versus Ti, Ni/(Cr + Mn) versus Ti + V, and Al + Mn versus Ti + V, and the geochemical similarities of biotite from Chating and other porphyry deposits, combined with the similarity of alteration assemblages, we conclude that Chating has porphyry Cu-Au affinities, but the hydrothermal system was affected by external fluids, in contrast to more typical subduction-related porphyry deposits.

The regional tectonic framework and some new understandings of the Middle-Lower Yangtze River Valley Metallogenic Belt

The regional tectonic framework and some new understandings of the Middle-Lower Yangtze River Valley Metallogenic Belt

Fluid Evolution of Fuzishan Skarn Cu-Mo Deposit from the Edong District in the Middle-Lower Yangtze River Metallogenic Belt of China: Evidence from Petrography, Mineral Assemblages, and Fluid Inclusions

The Fuzishan Cu-Mo deposit is located in the Edong district of the Middle-Lower Yangtze River Metallogenic Belt, China. The orebodies mainly occurred as lenticular and bedded shapes in the skarn zone between the Lower Permian Qixia Formation carbonate rocks and the quartz diorite. Four paragenetic stages have been recognized based on petrographic observations: (1) prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage, and (4) carbonate stage. Six fluid inclusion types were recognized: S1(vapor + liquid + halite ± other daughter minerals), S2(vapor + liquid + daughter minerals except halite), LV(rich liquid + vapor), VL(rich vapor + liquid), V (vapor), and L (liquid) types. Fluid inclusion studies show distinct variations in composition, final homogenization temperature, and salinity in four stages. Daughter minerals of the primary fluid inclusions include chalcopyrite, molybdenite, hematite, anhydrite, calcite, and halite in the prograde skarn stage and hematite, calcite, and sulfide (?) in the retrograde skarn stage. No daughter minerals occurred in the quartz-sulfide and carbonate stages. Final homogenization temperatures recorded in these stages are from 405 to &gt;550°C, from 212 to 498°C, from 150 to 485°C, and from 89 to 223°C, respectively, while salinities are from 3.7 to 42.5, from 2.6 to 18.5, from 2.2 to 17.9, and from 0.2 to 11.5 wt.% NaCl equivalent, respectively. The coexisting VLand S1type fluid inclusions show similar homogenization temperature of 550 to about 650°C in the prograde skarn stage, indicating that immiscibility occurred at lithostatic pressure of 700 bars to perhaps 1000 bars, corresponding to a depth of 2.6 km to about 3.7 km. The coeval VLand LVtypes fluid inclusions with homogenization temperature of 350 to 400°C in the late retrograde skarn and quartz-sulfide stages suggest that boiling occurred under hydrostatic pressure of 150 to 280 bars, equivalent to a depth of 1.5 to 2.8 km. Mo mineralization in the retrograde stage predated Cu mineralization which mainly occurred in the quartz-sulfide stage. Fluid compositions indicate that ore-forming fluid has highfO2and rich Cu and Mo concentration in the early stage, while relatively lowerfO2and poor Cu and Mo concentration in the middle to late stages. Microthermometric data show a decreasing trend in temperature and salinity in the fluid evolution process. Decreasing temperature and boiling event may be the main factors that control the ore precipitation.

Genesis of the Dongguashan skarn Cu-(Au) deposit in Tongling, Eastern China: Evidence from fluid inclusions and H-O-S-Pb isotopes

The Dongguashan copper-(gold) deposit is located in the Eastern Tongling ore district of the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYRB), Eastern China. The Cu-(Au) mineralization is associated with the Qingshanjiao quartz monzodiorite and consists of various types including stratiform, porphyry, vein-like and skarn. There are three deposit models, including: 1) stratabound skarn-type; 2) exhalative sedimentary (SEDEX)-hydrothermal superimposition-type; and 3) exhalative sedimentary (SEDEX) type. The ore-forming processes can be divided into the prograde skarn alteration (Stage I), retrograde alteration (Stage II) and quartz-carbonate alteration (Stage III). Four types of fluid inclusions (FIs) are recognized at Dongguashan: Vapor-rich two-phase aqueous (Type I), liquid-rich two-phase aqueous (Type II), daughter-mineral-bearing three-phase (homogenized to liquid by the disappearance of vapor phase; Type III), and daughter-mineral-bearing three-phase (homogenized to liquid by the disappearance of daughter minerals; Type IV). All four types of FIs are present in Stage II. Stage I does not contain Type IV FIs, and only Type II FIs are found in Stage III. For Stage I, Type I, II and III FIs homogenized at 379–548 °C, 319–522 °C and 450–512 °C, respectively, with salinities of 10.1–19.6, 5.9–19.4 and 36.7–43.3 wt% NaCl equivalent. For Stage II, Type I, II, III and IV FIs homogenized at 286–378 °C, 235–372 °C, 265–349 °C and 324–350 °C, respectively, with salinities of 1.4–17.0, 4.3–16.1, 34.7–40.6 and 34.4–41.0 wt% NaCl equivalent. The Type I to III FIs in Stage I and II have similar homogenization temperatures but different salinities, which indicates the occurrence of fluid immiscibility. Hydrogen-oxygen isotopes of the quartz (δD = −84.0 to −71.5‰, δ18OH2O = +4.51 to +8.97‰) and calcite (δD = −70.7 to −60.95‰, δ18OH2O = +4.41 to +4.91‰) suggest that the ore-forming fluids were principally magmatic-derived. δ34S values of the stratiform orebodies (+4.1 to +5.3‰), vein-like orebodies (+4.2 to +5.7‰), skarn orebodies (+4.9‰), porphyry orebodies (+5.1 to +5.7‰) and the Qingshanjiao pluton (−2.2 to +5.2‰) are different from those of the wall rocks (−29.5 to −4.6‰), suggesting that wall rocks were unlikely to be a major sulfur source. Lead isotopes of the sulfides from the different orebody types are similar to those of the plagioclase from the Mesozoic intermediate-felsic rocks in the MLYRB, suggesting that they have had similar Pb source. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magmatic source. The ore-forming fluid immiscibility during Stage I and II may have altered the physicochemical conditions of the hydrothermal fluid system, leading to the Cu-(Au) sulfide precipitation. Based on the ore geological and alteration/mineralization features, mineral assemblages, ore-forming material source and fluid evolution, we consider that Dongguashan is best classified as a porphyry–skarn Cu-(Au) deposit.

Ore-forming fluids and isotopic (H-O-C-S-Pb) characteristics of the Fujiashan-Longjiaoshan skarn W-Cu-(Mo) deposit in the Edong District of Hubei Province, China

The Fujiashan-Longjiaoshan deposit is located in the southern area of the Edong District of the Middle-Lower Yangtze River metallogenic belt. W-Cu-(Mo) orebodies are found in the contact zone between the granodiorite porphyry and Carboniferous to Triassic carbonate strata. Four stages of ore formation are identified: (1) the prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage (further subdivided into the early 3a and later 3b), and (4) carbonate stage. In this study, we applied fluid inclusion microthermometry, laser Raman spectroscopy, and H-O-C-S-Pb isotopic compositions to constrain hydrothermal processes and ore precipitation mechanisms of the Fujiashan-Longjiaoshan deposit. Early stage (1 and 2) ore-forming fluids belong to a high-temperature (above 550 °C), high-salinity (60–70 wt% NaCl equiv. and 15–20 wt% NaCl equiv, respectively), high-pressure (above 700 bars) and high-oxygen-fugacity NaCl-KCl-H2O system, and in the quartz-sulfide stage 3, the system changes into a NaCl-KCl-CO2-H2O system. Homogenization temperatures and salinities of ore-forming fluids gradually decrease throughout the evolutionary process. Fluid temperatures vary at >550 °C in prograde skarn stage 1, from 350 to 400 °C in retrograde skarn stage 2, from 250 to 300 °C in quartz-sulfide stage 3, and finally from 100 to 150 °C in carbonate stage 4. Salinity levels vary from 15 to 20 wt% NaCl equiv. in prograde skarn stage 1, from 5 to 20 wt% NaCl equiv. in retrograde skarn stage 2, from 10 to 15 wt% NaCl equiv. in quartz-sulfide stage 3a, from 5 to 10 wt% NaCl equiv. in quartz-sulfide stage 3b, and from 0 to 5 wt% NaCl equiv. in carbonate stage 4. The H-O-C isotopic compositions indicate that the ore-forming fluids were derived from magmatic water (δD of −123‰ to −83‰, δ18OV-SMOW of 6.1‰ to 7.4‰) with the input of meteoric water and organic matter in the quartz-sulfide stage (δD of −91‰ to −53‰, δ18OV-SMOW of 2.4‰ to 4.6‰, and δCV-PDB of −14.7‰ to −6.4‰). Sulfur and Pb isotopic compositions show that the ore-forming materials were mainly derived from granitic magma (δ34SV-CDT values of granodiorite-porphyry sulfides and skarns of −5.7‰ to +6.6‰) and in part from host sedimentary strata (δ34SV-CDT values of sulfides of country rocks clustering at −20‰ and at −10‰). Fluid boiling in the retrograde skarn stage gave rise to the first precipitation of scheelite. The precipitation of scheelite, chalcopyrite and molybdenite in the quartz-sulfide stage was probably triggered by the input of meteoric water and organic carbon. According to mineral assemblages and all available geological and geochemical data, we conclude that the Fujiashan-Longjiaoshan deposit is an oxidized skarn-type W-Cu-(Mo) deposit.

Major and Trace Element Geochemistry of Pyrite and Pyrrhotite from Stratiform and Lamellar Orebodies: Implications for the Ore Genesis of the Dongguashan Copper (Gold) Deposit, Eastern China

The Dongguashan copper (gold) deposit in Anhui Province is one of the largest copper (gold) deposits in the Tongling ore district, which is the most important region in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Stratiform and lamellar orebodies are the major deposit types. Pyrite and pyrrhotite from the stratiform deposit type (Py I, Po I) and lamellar deposit type (Py II, Po II) are investigated using Electron-probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Py I, Py II, Po I and Po II have high contents of Cu, Co, Au and Se, low contents of As, Pb and Zn, with Co/Ni ratios of 0.50−48.00, 4.00−45.00, 1.55−14.45 and 1.02−1.36, respectively, most of which are greater than 1 and vary widely; these characteristics are consistent with those of pyrite with a magmatic–hydrothermal origin. The higher Au/Ag and Fe/(S + As) ratios of pyrite and crystallization temperatures (286–387 °C) of hexagonal pyrrhotite indicate that the mineralization occurrs in environments with medium- to high-temperatures, high sulfur fugacity and medium-shallow depths. Therefore, we suggest that the Dongguashan copper (gold) deposit is a stratabound skarn-type ore deposit associated with magma intrusion activity during the Yanshanian Period.

The Cretaceous Huangdaoshan Cu-bearing intrusion in Chuzhou: Petrogenesis and implications for the Cu mineralization in the Middle–Lower Yangtze River Valley Metallogenic Belt, eastern China

The Huangdaoshan mineral deposit in the Middle–Lower Yangtze River Valley Metallogenic Belt, is located on the northern margin of the Yangtze Craton, eastern China. It is hosted by the high-K calc-alkaline quartz–monzonite porphyry and quartz–diorite porphyry of Huangdaoshan intrusion. The molybdenite Re–Os age for the mineral deposit suggests that mineralization occurred at 128.9 ± 2.3 Ma and was coeval with the ore-bearing intrusion (130 ± 1 Ma). Both porphyries are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in heavy rare earth elements (HREE) and high field-strength elements (HFSE), and have positive Eu anomalies. They also show adakitic affinities with high Sr (914–1227 ppm) and Sr/Y ratios (125–212), and low Y (5.40–9.00 ppm) and Yb (0.46–0.75 ppm) contents. Petrography, micro-fabric features, and Sr–Nd–Hf isotopic results suggest that these adakite-like magmas were derived from magma mixing between mantle- and crustal-derived materials. The strong REE fractionations as well as the high La/Sm (6.0–7.1) and intermediate Sm/Yb (4.5–5.6) ratios, suggest that hornblende crystallization was the dominant control on fractionation. Apparent temperatures based on Ti-in-zircon thermometry show that the mineralization-related porphyries crystallized at 711 °C –790 °C. The oxygen fugacity (fO2) estimated from hornblende Mg contents and biotite Fe3+, Fe2+ and Mg contents indicates that the mineralized magma possessed a high oxidation state (NNO + 0.15 to NNO + 1.62). The geochemical characteristics of the intrusions (enrichment in LILEs, depletion in HFSEs, and Nb–Ta anomalies) indicate that the mafic magma was derived from partial melting of the enriched lithosphere mantle, which had been metasomatized by slab-derived fluids from a subducted oceanic plate. Therefore, the parental magma contained high contents of H2O and metal (e.g., Cu), with high fO2. The extensive contemporaneous magmatism, metallogenic events, and volcanic basins in the region suggest an extensional tectonic setting. We further correlated this extension regime with slab roll-back of the Paleo-Pacific Plate.

The genesis of the Hehuashan Pb–Zn deposit and implications for the Pb–Zn prospectivity of the Tongling district, Middle–Lower Yangtze River Metallogenic Belt, Anhui Province, China

The Hehuashan lead–zinc deposit is located in the central Tongling Cu–Au–Mo mining district of eastern China and consists of stratabound ore bodies that are generally hosted by dolostone and limestone units of the Lower Triassic Lower Nanlinghu Formation. The deposit contains two types of sphalerite, namely tan to brown fine-grained (∼40 μm) type I sphalerite that is hosted by a dolomite, calcite, quartz and sericite gangue assemblage and colorless to brown coarse-grained (∼2 mm) type II sphalerite hosted within clasts in calcite-cemented breccias or within dolostone-hosted veins. Plotting these sphalerites in a Fe vs. Cd diagram indicates they have a similar composition as those within typical Mississippi Valley-type (MVT) deposits, suggesting that the Hehuashan deposit may have an MVT affinity. In addition, in-situ sulfur stable isotopic analysis of fine-grained (−7.8‰ to +3.0‰) and coarse-grained (+3.4‰ to +9.7‰) sphalerite indicates that the sulfur in the hydrothermal fluids that formed the deposit was derived from the country rocks within the Hehuashan area. Fluid inclusions within calcite and fluorite from the Hehuashan deposit have low homogenization temperatures (mean of 126 °C) and moderate salinities (mean of 7.1 wt% NaCl equivalent) that demonstrate the deposit formed from low temperature and moderate salinity hydrothermal fluids. This suggests that the Hehuashan deposit was almost certainly not formed from magmatic-hydrothermal fluids but instead was formed as a result of the mixing of basinal brines and meteoric water, again consistent with an MVT origin for this deposit. In summary, the Hehuashan lead–zinc deposit is an MVT deposit, suggesting that the Tongling district of Anhui Province, China is prospective for MVT mineralization and that the Triassic dolostones and limestones in this area represent high priority exploration targets for this style of mineralization.