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Geology, fluid inclusion, and stable isotope study of the skarn-related Pb–Zn (Cu–Fe–Sn) polymetallic deposits in the southern Great Xing’an Range, China: implications for deposit type and metallogenesis
Abstract
In recent decades, several skarn-related deposits have been found and explored in the southern Great Xing’an Range of China. To get a clear understanding of the characteristics and genetics of this type of deposit in this area, three of the largest, most typical, and most famous skarn-related deposits (Haobugao Pb–Zn deposit, Huanggang Sn–Fe polymetallic deposit, and Baiyinnuoer Pb–Zn deposit) are selected for systematically metallogenic study in this paper. The results of ore geology, fluid inclusion, and stable isotopes indicate that (1) most of the ore bodies of each deposit, occurred in the outer contact zone of the magma intrusion and Permian strata, fine vein disseminated mineralization within the intrusions were also found in this study. Mineralization of these deposits all show closely temporal, spatial, and genetic relationships with skarns. (2) Fluid inclusion petrography and microthermometry results show that the fluid inclusion assemblages developed in the different mineralization stages of each deposit changed from Type-S (daughter mineral-bearing three-phase fluid inclusions) + Type-V (vapor-rich fluid inclusions) + Type-L (liquid-rich fluid inclusions) to Type-V + Type-L and eventually evolved into L-Type. Correspondingly, the ore-forming fluids changed from medium to a high-temperature, high-salinity, and boiling fluid system and then to a low-temperature, low-salinity, and uniform fluid system. The types of fluid inclusions in garnets are consistent with those in quartz phenocrysts of Mesozoic granites, indicating that the formation of skarns is directly related to Mesozoic magmatic activity. (3) The δ³⁴S values of ores from the above three deposits all exhibit a narrow variation range (changes are mainly around 0‰) and greatly differ from the SEDEX-type deposits in China. The lead isotope compositions of the sulfide minerals are also consistent with those of Mesozoic granites. These previous characteristics suggest that both of the ore-forming fluids and the ore-forming materials were of magmatic origin. Consequently, the Haobugao, Baiyinnuoer, and Huanggang deposits are all skarn-type deposits, which are related to Mesozoic magmatic activities in terms of ore geology features, ore-forming fluids, and ore-forming material.
... In practice, however, magma bodies emplaced at shallow levels in the earth's crust may interact with meteoric water (Rye and Ohmoto 1974). Ore-forming fluids of typical skarn deposits (e.g., Haobugao and baiyinnuoer) in the SGXR also have low ␦D values (Fig. 9), possibly related to the mixture of magmatic fluid and meteoric water (Wang et al. 2018). Water-rock interactions can also cause a de- (Wang et al. 2018) and Haobugao (Li et al. 2015) deposits are also plotted). ...
... Ore-forming fluids of typical skarn deposits (e.g., Haobugao and baiyinnuoer) in the SGXR also have low ␦D values (Fig. 9), possibly related to the mixture of magmatic fluid and meteoric water (Wang et al. 2018). Water-rock interactions can also cause a de- (Wang et al. 2018) and Haobugao (Li et al. 2015) deposits are also plotted). The primary magmatic and metamorphic water boxes are from Barnes (1979) and Sheppard (1986), and the meteoric water line is from Craig (1961). ...
The Changlingzi Pb–Zn deposit is located in the southern Great Xing’an Range metallogenic belt of Northeast China. This deposit experienced two types of mineralization including skarn (ore block I) and hydrothermal vein (ore block II), and their orebodies are hosted mainly in the Lower Permian Zhesi Formation. The hydrothermal mineralization is classified into two metallogenic periods: skarn (stage 1) and sulfide (stages 2, 3, and 4). The skarn period affected only the ore block I, whereas the sulfide period similarly affected the two ore blocks. Fluid inclusion studies indicate that the ore-forming fluids during the early stage were medium-to high-temperature, high-salinity heterogeneous NaCl–H2O fluids, and that they eventually evolved to low-temperature, low-salinity homogeneous NaCl–H2O fluids by late stage. Studies of the hydrogen and oxygen isotope compositions (γ¹⁸OH2O = −13.85‰ to 3.95‰, γDH2O = −132.8‰ to −102.7‰) show that the ore-forming fluids gradually evolved from magmatic water to meteoric water. Sulfur and lead date suggest that the ore-forming materials were probably derived from deep magma and the Permian strata. Although our data show that ore blocks I and II, in terms of genesis, were skarn-and medium-to low-temperature hydrothermal vein-types, respectively, the ore-forming fluids of both ore blocks were the same period, and the differences in mineralization type can be related to the wall rocks.
... High-temperature hydrothermal systems (e.g., skarn and magmatic-hydrothermal deposits) exhibit smaller Cd isotopic variations than low-temperature hydrothermal systems (e.g., MVT deposits). Skarn and magmatic-hydrothermal deposits, such as the Baiyinnuoer (166-480°C; Wang et al., 2018) and Shagou (157-267°C; Li et al., 2013) deposits, exhibit the range of δ 114/110 Cd NIST-3108 values of 0.26 to 0.01‰ and 0.06 to 0.01‰, respectively . MVT deposits, such as the Fule (93-200°C; Liang, 2017) and Daliangzi (213-283°C;Wu, 2013) deposits, exhibit greater range of δ 114/110 Cd values of 0.06 to 0.58‰ (Zhu et al., 2017 and 0.22 to 0.32‰ , respectively (Table S1). ...
Metal stable isotopes (e.g., Zn, Cd, and Cu) have been used to track metal sources in different types of hydrothermal systems. However, metal isotopic variations in sulphides could be triggered by various factors such as mineral precipitation and fluid mixing. Thus, tracking the metal sources of hydrothermal systems is still a big challenge for metal isotopes. In this study, we investigated the Cd isotopic systematics of sphalerite from the Nayongzhi Zn–Pb deposit, which is a Mississippi Valley‐type (MVT) deposit in the Sichuan–Yunnan–Guizhou mineralization province (SYGMP). We reinterpreted the published S isotope data for the SYGMP and found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. As such, a model that involves mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction (TSR) can explain the ore formation in the Nayongzhi deposit. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing, and thus the Cd isotopic variations of sphalerite were inherited from the source rocks. The large range of Zn/Cd ratios and uniform Cd isotopic compositions of the sulphides are similar to those of igneous rocks but different from those of sedimentary rocks, indicating that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Our results reaffirm that metal stable isotopes, particularly Cd isotope compositions of sphalerite, are powerful geochemical tracers for investigating the formation mechanisms of ore deposits.
... Previous studies have focused on the Pb-Zn skarn-related geology, chronology, and fluid inclusions [32][33][34][35][36], with minor focus on Sn mineralization in the skarns [37]. Except for Fe skarn, Fe-Zn skarn, and Pb-Zn-(Cu) skarn, minor Sn and W mineralization is also reported, not only in the skarns, but also in the granite porphyry of the surrounding area. ...
Metal migration and precipitation in hydrothermal fluids are important topics in economic geology. The Hongling polymetallic deposit comprises one of the most important parts of the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt, which is in eastern Inner Mongolia. Except for lead–zinc skarn, minor cassiterite in the skarn and disseminated W–Sn mineralization in granitic rocks have also been found. The dominant Sn–W mineralization is in the northern part of the deposit, occurring as disseminated wolframite and cassiterite in aplite hosted in Mesozoic granite porphyry. The aplite together with pegmatite K-feldspar–quartz comprises vein dikes hosted in the granite porphyry, providing evidence for the transition from melt to fluid. The veins, dikes, and Sn–W mineralization in the aplite provide an opportunity to investigate fluid exsolution and the mechanics of metal precipitation. Based on field observations, the micrographic and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) results of the vein dikes, chronology, and the whole-rock geochemistry of the host rock, together with the fluid inclusion results, this paper discusses the characteristics of the causative magma, the mechanics of fluid exsolution and W–Sn precipitation. Our results show that the causative magma is of highly fractionated A-type granite affinity and has an intrusive age of late Mesozoic (133.3 ± 0.86 Ma). The magmatic evolution during shallow emplacement led to immiscibility between highly volatile, high-silica, and W- and Sn-enriched melts from the parent magma, followed by fluid exsolution from the water-rich melt. The alkaline-rich fluid exsolution led to a change in the redox state of the magma and the chilling of the melt. Fluid boiling occurred soon after the fluid exsolution and was accompanied by the degassing of CO2. The boiling and escape of CO2 from the fluid led to changes in fluid redox and W and Sn precipitation; thus, the W and Sn mineralization are mostly hosted in causative intrusions or peripheral wall rocks, which can be used as indicators for Sn–W exploration in the area.
... Due to the significant Sn, Zn, and Pb resources, this ore district is considered to be the most important Sn-Zn-Pb polymetallic metallogenic zone in the Great Xing'an Range metallogenic province (Shao et al., 2007;Zeng et al., 2011;Shu et al., 2013). Moreover, this district is characterized by numerous skarn-type deposits, e.g., the Haobugao Zn-Pb deposit, the Huanggang Fe-Sn deposit, and the Baiyinnuo'er Zn-Pb deposit, which are all associated with Mesozoic magmatic intrusions emplaced in the Permian carbonates (Shu et al., 2013;Zhai et al., 2014b;Jiang et al., 2017;Wang et al., 2018d). ...
The Haobugao skarn Zn-Pb ore deposit (reserves of 0.29 Mt @ 4.24% Zn, 0.15 Mt @ 2.25% Pb) is located in the southern Great Xing’an Range (SXGR) Cu-Mo-Ag-Au-Pb-Zn-Fe metallogenic province in northeastern China. The ore bodies mainly occur near the contact zones between the early Cretaceous granite and the lower Permian carbonates and sometimes in distal locations. Two types of garnet are identified, i.e., green and fine-grained garnet (Grt A), and brown and coarse-grained garnet (Grt B). The Grt A contains a wider compositional range (Adr71.46-95.07Grs0.16-24.10), whereas the Grt B contains a relatively narrow compositional range (Adr87.65-97.52Grs0.07-10.11). The Grt A displays chondrite-normalized HREE-enriched and LREE-depleted patterns with negative Eu anomalies, suggesting that the Grt A was likely crystallized from a nearly neutral fluid. In contrast, the Grt B is LREE-enriched, HREE-depleted with pronounced positive Eu anomalies, indicating that the Grt B was probably formed from a mildly acidic fluid. The Grt A contains lower U contents than the Grt B, implying that the Grt A was likely formed under a relatively oxidized condition, while the Grt B crystallized from a more reduced condition.
Skarn mineralization at Haobugao (139.10 ± 5.40 and 140.70 ± 1.89 Ma, garnet LA-ICP-MS U-Pb ages) and Zn-Pb mineralization (138.27 ± 0.14/0.69/0.81 and 138.82 ± 0.07/0.68/0.80 Ma, molybdenite ID-N-TIMS Re-Os ages) were associated with the emplacement of the granitoids dated from 143.49 ± 0.76 to 140.85 ± 0.75 Ma (zircon LA-ICP-MS U-Pb ages). The integrated geochronological data suggest that the ore-related granitoids, skarn, and Zn-Pb mineralization in the Haobugao deposit all formed in the early Cretaceous, which occurred in an extensional tectonic setting associated with regional Paleo-Pacific slab roll-back. This study highlights the reliability and viability of garnet U-Pb dating for constraining the timing of skarn formation, and utilizing its age with textural and trace element concentrations could well reconstruct the ore-forming process of skarn deposits.
... On the basis of their mineral assemblages, host rocks and major ore controlling factors, the major deposits of Early Cretaceous from SGXR can be divided into the following three types: (1) skarn type deposits, (2) porphyry type deposits, and (3) hydrothermal vein type deposits [11] . During the past years, we have successively carried out studies on geology, fluid inclusion, stable isotope, lithogeochemistry, and geochronology metallogenic prediction of the major Early Cretaceous deposit in the area [12][13][14][15] . In this paper, we reviewed the geology, fluid inclusion and isotope characteristics of the Early Cretaceous hydrothermal Pb-Zn and associated metal deposits, and the temporal, spatial and genetic relationships between different types of ore deposits. ...
The southern Great Xing’an Range (SGXR) is one of the most important non-ferrous metal ore concentrating areas in China, and a large number of Pb-Zn and associated metal deposits have been found and mined in this area. The Early Cretaceous deposits of SGXR can be divided into three principal types according to their geological characteristics: skarn type deposits, porphyry type deposits and hydrothermal vein type deposits. In this contribution, we list some important Early Cretaceous deposits in the SGXR and summarize their geological characteristics. Research of stable isotope and fluid inclusion reveal that the sources and properties of ore-forming fluids varied between different types of mineral deposits, while the sources of ore-forming materials of different deposits are similar(characterized by deep-seated magmatic activities). We therefore conclude that the Early Cretaceous porphyry, skarn and hydrothermal vein type deposits in SGXR belong to a unified metallogenic series and developed a synthetical model for these deposits.
A considerable type of deposits, including those for W, Sn, Mo, and Cu, are found in the skarn. Skarn mineralization can be found southwest of Miass City, near the boundary between marble deposits and diorite in massive complex. We describe the Skarn’s petrography and geochemistry in this research. For our geochemical analysis with ICP-MS, EMPA, and X-ray spectral fluorescence analysis and petrography study, we collected samples of both the skarn and igneous rocks in the Syrostan massive. Petrography study revealed that garnet, epidote, amphibole, and pyroxene dominate skarn mineralization. Garnet and pyroxene minerals represent early metasomatic stage, indicating a prograde stage of alteration. Retrograde alteration, is distinguished by the presence of epidote, quartz, calcite, and chlorite. The skarn is associated with Syrostan massive, which dominant by metaluminous I-type granite and high-K calc-alkaline series granitic rocks. In comparison to igneous rocks granite and diorite, the skarn sample showed high enrichment in HREE. Skarn samples appeared to have higher concentrations of Mo, W, Sn, Ta, and Nb than igneous rocks form the Syrostan massive. skarn mineralization containing iron oxides, the Co/Ni ratios in the iron oxide (2.5 to 5.5) describe how the hydrothermal process affects the magmatic source. Based on these findings, we propose that W, Sn, and iron oxide mineralization may occur in skarn.
he Pusangguo Cu–Pb–Zn skarn deposit is a representative Co-bearing deposit in the Gangdese metallogenic belt. The mineralization mainly has a close relationship with the biotite granodiorite. Here we identified four paragenetic stages during the ore formation: prograde skarn stage (stage 1) dominated by garnet and less diopside, retrograde stage (stage 2) which is characterized by epidote, chlorite and actinolite, quartz polymetallic sulfide stage (stage 3) featured by chalcopyrite, sphalerite, galena with minor cobaltite and aikinite, and quartz calcite stage (stage 4). In this study, fluid inclusion, H–O, He–Ar, S and Pb isotope compositions were determined to constrain the sources and evolution of the ore-forming fluids, metal deposition mechanisms and metallogenetic model for the Pusangguo deposit. The He–Ar isotopic compositions (³He/⁴He = 0.39–0.55 Ra, ⁴⁰Ar/³⁶Ar = 299–366) show that the ore-forming fluids predominantly derived from crust source with minor mantle input. The H–O isotopic analysis results (δ¹⁸OH2O = −13.3 to +4.9‰, δD = −168 to −79.5‰) suggest that the ore-forming fluids were sourced from a magmatic origin that mixed with some meteoric water. The S–Pb isotopic results suggest that the ore-forming materials were mostly derived from the upper crust with a minor amount of mantle materials and the biotite granodiorite magma contributed most of the lead and possibly other metals. Fluid inclusion petrography and microthermometry results show that the fluid inclusion assemblages developed in the different mineralization stages of Pusangguo deposit changed from type II (vapor-rich two-phase fluid inclusions) + type III (daughter mineral-bearing three-phase fluid inclusions) to type I (liquid-rich two-phase fluid inclusions) + type II + type III + type IV and eventually evolved into type II. Correspondingly, the ore-forming fluids mainly belonged to H2O-NaCl solutions and changed from high temperature (413–532°C), moderate–high salinity (15.5–53.1 wt.% NaCl equiv.) fluid system in stage 1 to a lower-temperature (176–234°C) and lower-salinity (0.7–4.2 wt.% NaCl equiv.) meteoric water during stage 4. Fluid boiling and mixing were likely the vital factors controlling the metal precipitation.
The Southern Great Xing'an Range (SGXR) hosts a number of Early Cretaceous Sn and associated metal deposits, which can be divided into three principal types according to their geological characteristics: skarn type deposits, porphyry type deposits and hydrothermal vein type deposits. Fluid inclusion assemblages of different types of deposits are quite different, which represent the complexities of metallogenic process and formation mechanism. CH4 and CO2 have been detected in fluid inclusions from some of deposits, indicating that the ore‐forming fluids are affected by materials of Permian strata. Hydrogen and oxygen isotope data from ore minerals and associated gangue minerals indicate that the initial ore fluids were dominated by magmatic waters, some of which had clearly exchanged oxygen with wall rocks during their passage through the strata. The narrow range for the δ34S values presumably reflects the corresponding uniformity of the ore forming fluids, and these δ34S values have been interpreted to reflect magmatic sources for the sulfur. The comparation between lead isotope ratios of ore minerals and different geological units’ also reveals that deeply seated magma has been a significant source of lead in the ores.
The Mianeh iron skarn deposit lies in the Arasbaran region within the Qaradagh metallogenic district, NW Iran. This high-grade massive magnetite skarn originated by the interaction of Upper Cretaceous limestone with metasomatic ore-bearing fluids associated with hypabyssal Oligo-Miocene quartz diorite. Mineral chemistry of the primary clinopyroxenes demonstrates the sub-alkaline, volcanic arc setting of magmatism. Two general stages of skarnification are recognized: (1) silicate skarn (stage I) is composed essentially of grossular and low-Fe diopside formed before the main mineralization and (2) magnetite-garnet skarn (stage II) composed of strongly anisotropic coarse-grained garnets with a narrow compositional zoning radially formed by addictive infiltrating of silica and iron-rich metasomatic fluids which overprint and/or crosscut the early stage silicate skarn. Anhydrous prograde calc-silicate assemblages were replaced by a series of hydrous calc-silicates (epidote, tremolite-actinolite) and/or quartz, calcite, magnetite, hematite, and pyrite. Magnetite (±hematite) is the dominant hypogene ore mineral that initially precipitated coincident with the late prograde to the early retrograde metasomatic stages. Mineralogical studies suggest that silicate skarn formation commenced at temperatures about 560 °C, X(CO2)fluid ≤ 0.15, αSiO2∼−1.0, and fluid pressure 1.0 kbar. The magnetite-garnet skarn formed from H2O-rich fluids [X(CO2)fluid < 0.1] at a temperature of 525 to 450 °C and maximum log ƒO2 between −20.2 and −23. During the late stages of prograde skarn development, the stability field of andradite shifted to low ƒO2 and ƒS2 conditions resulting in main iron ore deposition (as magnetite). The andradite replacement temperature and presence of pyrite (instead of pyrrhotite) suggest that logƒS2 remained constant at about −6 to −7 during cooling of the system.
The Sarvian Fe skarn deposit is located in the Urumieh–Dokhtar magmatic arc, western Iran. The Sarvian quartz diorite intruded the surrounding Permian to Tertiary limy formation, culminated in thermal metamorphism as well as skarnification in which the Sarvian deposit formed. Microthermometry studies in the Sarvian skarn deposit reveal two distinct inclusion groups; group A with medium–high temperature and hypersaline and group B with low–medium temperature and low salinity. Group A inclusions which are entrapped during formation of prograde are thought to be derived from the magmatic source. Fluid boiling and subsequent developing of hydraulic fracturing led to inflow and/or mixing of early magmatic fluids (group A) with circulating groundwater culminated in formation of low salinity and low temperature fluid inclusions (group B) during the formation of retrograde assemblage. Fluid inclusion thermometry reveals the formation temperature and the salinity of 300–370 °C and 31–33 wt% NaCl for the prograde stage and 180–230 °C and 1–15 wt% NaCl for the retrograde stage of skarnification at Sarvian skarn rocks. Fe-mineralization as well as hydrothermal minerals occurred during retrograde metasomatism. The estimated depth and pressure of occurrence for prograde stage are 1000–1200 m and 100–150 bars, and for retrograde stage, these are about 200 m and 50 bars, respectively. Garnet and pyroxene, as the main constituent minerals of prograde stage, are the most informative minerals offering a suitable tool to constrain the skarnification conditions. Garnets in the Sarvian deposit are mainly grossular and andradite, showing both normal and inverse zoning as the result of variation in their chemical composition. Such types of zoning represent alternation of high acidity oxidation and low acidity oxidation conditions that were prevailed on skarnification in the Sarvian prograde assemblage. Also, chemical composition of the Sarvian pyroxenes shows an alternation of high oxygen fugacity and low oxygen fugacity conditions for their formation. This is also supported by fluctuation of the ratios of andradite to grossular and diopside to hedenbergite, denoting to an obvious shifting that was prevailed between oxidizing and redox conditions during formation of prograde assemblage in the Sarvian. Garnet–pyroxene thermometry determines the formation temperature of prograde assemblage between 370 and 550 °C at Sarvian skarn rocks which is verified also by fluid inclusion thermometry. Decomposition of limestone by reaction of high-temperature hydrothermal fluids with carbonate host rock resulted in injection of CO2 into the Sarvian system that caused oxidation, changing Fe⁺² to Fe⁺³ culminated in the magnetite deposition.
This study presents some new discoveries of the porphyritic quartz in the Aolunhua Cu-Mo deposit, southern segment of Da Xing' an Mountains. Based on the study on the texture, genesis and fluid inclusions in porphyritic quartz, together with the characteristics of hydrothermal veins, the processes of fluids exsolution, evolution and mineralization have been revealed. Porphyritic quartzes are divided into two groups; ( I ) individual porphyritic quartz and ( II ) polycrystal quartz aggregate, characterized by widespread daughter minerals-bearing fluid inclusions, and are of a special product during magmatic-hydrothermal transition. Fluid inclusions data show that a H 2O-CO2-Na-K-Ca-Fe-Cu-Ti-dominated initial fluid with high temperature ( >492CC) and high salinity (up to 47. 6% -58. 7% NaCleqv) separates from magmatic system under the condition that pressure ≥115MPa and depth &4.3km. In hydrothermal stage, fluid boiling results from sharp decrease of pressure, coupled with temperature reduce, lead to large scale mineralization. Characteristics of minerals in veins and microthermometry data demonstrate molybdenite precipitation temperature is above 335°C. The uplift, supported by data of fluid inclusions in porphyritic quartzes, is more than 4. 3km, indicating that the uplift rate is at least 32.6m/Ma. So, the porphyritic quartz can be used to guide exploration as an indicator of fluid exsolution from porphyry, and also provides significant constraints on regional geology evolution.
The northern and southern margins of North China Craton are the important molybdenum metallogenic belts in China, and a lot of molybdenum deposits were discovered in these two belts in recent years, this indicate that these belts have a huge exploration potential. The Triassic molybdenum deposits catch geologist's eye. The Triassic molybdenum deposits distribute along the northern margin, southern margin and adjacent area of North China Craton. The molybdenum deposits are controlled by regional EW-, and NW-trending faults, and is associated with acid granites and carbonitite dykes in time and space. The molybdenum deposits are usually distributed in granite body, along the endo-or exo-contaet zones of the ore-forming rock body, or nearby. The molybdenum deposits can be classified into two types; porphyrYand vein type. The vein type deposits are divided into two subtypes; quartz vein and carbonitite vein type deposits. The geochronology data shows that the molybdenum deposits in the northern margin and southern margin ol the North China Craton and adjacent area were formed in 248 ∼ 220Ma, and 226 ∼ 210Ma, respectively. The coiresponding geodynamic background is the syn-collisional and post-collisional extension of the newly-amalgamated North China-Siberian plates during Indo-Chinese epoch, and syn-collisional setting of the amalgamated North China-Yangtze plates.
Plumbotectonics is an attempt to model the geochemical behaviour of U, Th and Pb, among major terrestrial reservoirs in agreement with observational data. By recycling rock through the orogenic environment, a dynamically communicating upper crust, lower crust, and mantle can produce the required patterns of lead-isotope evolution.
: The Bianbianshan deposit, the unique gold-polymetal (Au-Ag-Cu-Pb-Zn) veined deposit of the polymetal metallogenic belt of the southern segment of Da Hinggan Mountains mineral province, is located at the southern part of the Hercynian fold belt of the south segment of Da Hinggan Mountains mineral province, NE China. Ores at the Bianbianshan deposit occur within Cretaceous andesite and rhyolite in the form of gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite, chalcopyrite, galena and sphalerite. The deposit is hosted by structurally controlled faults associated with intense hydrothermal alteration. The typical alteration assemblage is sericite + chlorite + calcite + quartz, with an inner pyrite – sericite – quartz zone and an outer seicite – chlorite – calcite – epidote zone between orebodies and wall rocks. δ34 S values of 17 sulfides from ores changing from –1.67 to +0.49‰ with average of –0.49‰, are similar to δ34 S values of magmatic or igneous sulfide sulfur. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb data of sulfide from ores range within 17.66–17.75, 15.50–15.60, and 37.64–38.00, respectively. These sulfur and lead isotope compositions imply that ore-forming materials might mainly originate from deep sources. H and O isotope study of quartz from ore-bearing veins indicate a mixed source of deep-seated magmatic water and shallower meteoric water. The ore formations resulted from a combination of hydrothermal fluid mixing and a structural setting favoring gold-polymetal deposition. Fluid mixing was possibly the key factor resulting in Au-Ag-Cu-Pb-Zn deposition in the deposit. The metallogenesis of the Bianbianshan deposit may have a relationship with the Cretaceous volcanic-subvolcanic magmatic activity, and formed during the late stage of the crust thinning of North China.
LA-ICP-MS zircon U–Pb dating and geochemical data have been obtained from five representative mafic–ultramafic intrusions in the Lesser Xing'an–Zhangguangcai Range, NE China, with the aim of improving our understanding of the Mesozoic tectonic evolution in the region, and in particular, determining the time of initiation of the circum-Pacific tectonic system. The selected zircons exhibit striped absorption in cathodoluminescence (CL) images and have high Th/U ratios (0.20–3.16), indicating a magmatic origin. The zircon U–Pb dates indicate that most of these magmatic zircons (other than a few relics that were captured and entrained in the magma) formed in the late Early Jurassic (186–182 Ma), and not as previously supposed in the Middle Caledonian. The five mafic–ultramafic plutons are composed of olivine-gabbro, hornblendite, gabbro, hornblende-gabbro, and gabbro–diorite. The olivine-gabbro and hornblendite display cumulate textures, implying that fractional crystallization of olivine and plagioclase took place during magma evolution. These mafic–ultramafic igneous rocks have SiO2 = 37.3%–55.7%, MgO = 3.05%–13.3%, Al2O3 = 11.8%–23.8%, Mg# = 42–69 [Mg# = 100Mg / (Mg + Fe2 +total)], and δEu = 0.88–1.32, and they display three types of rare earth element (REE) distribution patterns: right-slipped, flat patterns, or dome-like. The trace element spider diagrams show that the rocks are enriched in large ion lithophile elements (LILEs) such as Ba, K, and Sr, and depleted in high field strength elements (HFSEs) such as Nb, Ta, Zr, and Hf. The zircons have εHf (186–182 Ma) = + 2.7 to + 12.0, and TDM1 = 366–732 Ma. The geochemical data indicate that the Early Jurassic mafic magma originated in an extensional environment from the partial melting of a depleted mantle wedge that had been metasomatized by fluids released from a fossil subducted slab. These data, combined with information on the spatial variation of coeval igneous rocks, indicate that the formation of the Early Jurassic mafic–ultramafic rocks in the Lesser Xing'an–Zhangguangcai Range was related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent, and this event would mark the beginning of the circum-Pacific tectonic system.
The Tianbaoshan Pb–Zn–Cu–Mo deposit is located in the eastern part of Jilin–Heilongjiang region, NE China which is considered to be the eastern segment of the Central Asian Orogenic Belt. Field and geochronological evidences indicate this deposit experienced three types of mineralization including Hercynian skarn, cryptoexplosion breccia pipe, and Yanshanian quartz vein. The early stages of the Pb–Zn–Cu mineral systems in skarn and cryptoexplosion breccia pipe are characterized by a high-temperature, high-salinity H2O–CO2–NaCl system of hydrothermal fluids that were possibly exsolved from the Hercynian wall-rock granodiorite. These fluids show H–O isotopic compositions similar to those of typical magmatic fluids. By contrast, the low-temperature hydrothermal fluids of the later stages are represented by low-salinity NaCl–H2O systems with low H–O isotopic values. The skarn and cryptoexplosive breccia pipe types of Pb–Zn–Cu mineralization tend to have weakly negative δ³⁴S values of –4.0‰ to –0.8‰ (mean values of –2.31‰ and –2.16‰, respectively), indicating that the sulfur was sourced from the Hercynian magma. Therefore, the early stage ore-forming fluids of the skarn and cryptoexplosive breccia pipe were most likely sourced from high-temperature and high-salinity fluids closely related to the cooling and fractional crystallization of the Hercynian granodiorite, while the later stages changed to NaCl–H2O meteoric water influx. Whereas the ore-forming fluids of the quartz vein type of Mo mineralization were high-temperature, high-salinity NaCl–H2O systems that differed from those of the skarn and cryptoexplosion breccia pipe, but their H–O isotopic compositions also indicate a magmatic fluid. The weakly enriched δ³⁴S values of molybdenite from the quartz vein type Mo mineralization (δ³⁴S = 0.2–2.8‰, average of 1.65‰) are comparable with those of other Mesozoic Yanshanian Mo deposits (δ³⁴S = 0.4‰– 4.1‰, with an average of 1.39‰–3.15‰), but differ significantly from those of the Hercynian Pb–Zn–Cu skarn and cryptoexplosion breccia pipe. This indicates that the sulfur of quartz vein type of Mo originated from Mesozoic Yanshanian magmatism and that the ore-forming fluids were derived from Yanshanian magmatic rocks rather than being a product of the Hercynian activity. The δ¹³C values of the fluid inclusions in quartz from the skarn, cryptoexplosion breccia pipe and quartz vein types are in a narrow range of –19.5‰ to –9.3‰, similar to those of the Shanxiuling Group, which indicates that the carbon of the three types of mineralization had the same primary origin in the Shanxiuling Group. The lead isotope compositions of ores from the skarn and cryptoexplosion breccia pipe types of mineralization (²⁰⁶Pb/²⁰⁴Pb = 18.0725– 18.3627, ²⁰⁷Pb/²⁰⁴Pb = 15.3721–15.5694 and ²⁰⁸Pb/²⁰⁴Pb = 37.5542–38.8208) overlap with those of the Hercynian granodiorite and Shanxiuling Group marble, suggesting that the lead was probably derived from a mix of two different sources, the Shanxiuling Group and the Hercynian granodiorite. Whereas the lead isotope compositions of ores from the quartz vein type of Mo mineralization (²⁰⁶Pb/²⁰⁴Pb = 18.3837–18.6949, ²⁰⁷Pb/²⁰⁴Pb = 15.6824–15.7293 and ²⁰⁸Pb/²⁰⁴Pb = 39.1009–39.1889) are significantly higher than those of the Shanxiuling Group marble and the Hercynian granodiorite. This indicates that the lead may be a product of Yanshanian magmatic activity instead of the nearby Hercynian granodiorite.
Zhenzigou Pb-Zn deposit is a representative one of Qingchengzi Pb-Zn ore field. The deposit mainly occurs in Gaojiayu and Dashiqiao Formation, and is controlled by strata, magmatism, and tectonism with the main ore types being stratiform, stratoid, and veined ore bodies. The deposit experienced three metallogenic episodes such as submarine exhalation, metamorphism or deformation, and hydrothermal superposition. Hydrothermal superposition mineralization played an important role in the formation of the veined ore bodies and the local hydrothermal transformation of stratiform ore bodies. It can be classified into two stages: pyrite-galena-sphalerite-quartz (stage I) and pyrite-galena-quartz-calcite (stage II). According to the fluid inclusions and C-D-O isotope research, aqueous two-phase is developed in stage I with minor vapor-rich and CO2-bearing three-phase in the quartz fluid inclusions, and the ore-forming fluids are of middle-low temperature, low salinity, and low density CO2-H2O-NaCl system with enrichment of H2O, CO2, CH4, and N2. The δDH2O-SMOW, δ18OH2O-SMOW and δ13C of the fluid inclusions in the quartz are -96.5‰ and -95.4‰, -0.62‰ and 0.04‰, -4.8‰ and -4.4‰ respectively, which shows some characteristics of a fluid mixture of meteoric water and magma water. In stage II, aqueous two-phase fluid inclusions are developed in quartz; and the ore-forming fluids are of the low temperature, low salinity and low density H2O-NaCl system, containing a small amount of CO2, CH4, and N2. The δDH2O-SMOW and δ18OH2O-SMOW of the fluid inclusions in the quartz are -88.4‰--80.0‰ and -7.93‰--5.57‰ respectively, which shows the characteristics of meteoric water with δ13C of -12.6‰--7.9‰, a characteristics of magma water. Based on the above, we can infer that in the early mineralization stage, the ore-forming fluids were the mixture of meteoric water and magmatic water in Yanshan period, and in the late mineralization stage the blending proportion of meteoric water increased.
Exhalative mineralizations are frequently associated with various types of exhalites that often provide important evidence for ore genesis. The southern segment of the Da Hinggan Mountains is a well-known tin-polymetallic metallogenic belt of North China where Jurassic-Cretaceous volcanic-plutonic rocks are widespread. Based on this fact, most of the ore deposits were regarded as epigenetic hydrothermal deposits in genetic connection with the Mesozoic magmatism. However, nearly 90% of the deposits occur in Permian strata implying a close relation between mineralization and Permian strata. Case studies were made on the Huanggang Fe-Sn deposit and the Dajing Sn-polymetallic deposit. In combination with geochemical data, detailed geological, fabric, petrographical and mineralogical studies on the exhalites associated with ores demonstrated that subaqueous exhalative mineralization did occur during the basin evolution at the Permian time in the southern segment of the Da Hinggan Mountains, which is ignored and poorly understood, but might be as important as the hydrothermal mineralization connected with the Mesozoic magmatism. The stratiform skarns in the Huanggang deposit presents a peculiar example of exhalites. The siderite-sericite chert in the Dajing deposit, regarded as Mesozoic rhyolite porphyry before this study, is a new type exhalite formed in a lacustrine basin and closely associated with sulfide ore characteristic of complex metal assemblage of Sn-Ag-Cu-Pb-Zn. Exhalite is apparently one of the most important petrological evidences for exhalative mineralization.
The Taihang - Da Hinggan Mountains Tectonomagmatic Belt is the Mesozoic magmaeric activities concentrating area in eastern China, which passes through the two tectonic units of the North China Craton and the Inn Mongolian Orogenic Zone. In this paper a systematic geochemical study on Nd, Sr and Pb isotopic characteristics from more than 40 typical complexes along the tectonomagmatic belt is presented to indicate that the Mesozoic intrusives in different sections of this belt (mainly the north, south Taihang Mountains and the middle-south Da Hinggan Mountains), even those of different stages (mainly three stages) in the same section have entirely different Nd, Sr and Pb isotopic characteristics, which reveals that their source regions are different. The source rocks in the southern section of Taihang Mountains are related to materials from the enriched mantle reservoir. In the northern section the early stage basic-intermediate rocks are mainly formed by the partial melting of materials from the enriched mantle, the main stage intermediate-acid ones have a close connection to materials from the lower crust, while the late stage alkali-rich ones are even derived from those from the lower-middle crust. And the intermediate-acid magma in the middle-south Da Hinggan Mountains is mainly originated from depleted mantle materials. These also reveal that the lithospheric mantle below the North China Craton is enriched and that below the Inner Mongolia Orogenic Zone is depleted. In addition, implicated by Nd depleted mantle model ages (TDM) , 2543 ∼ 1485Ma probably represents the time for mantle enrichment beneath the North China Craton, and 983 ∼ 540Ma (Proterozoic to early Palaeozoic period) suggests one of the main stages for the crust growth in Da Hinggan Mountains area.
Hongling lead-zinc polymetallic deposit share many similarities with others from the southern Daxinganling polymetallic metallogenic belt. There are two types of molybdenum mineralization in the mining area, including porphyry and skarn. The former, displaying spot-disseminated feature, occurs in granite porphyry, whereas the latter, displaying film like feature, occurs in quartz. The metallogenic age of Hongling deposit can be constrained from Re-Os isotopic dating of the two kinds of molybdenite. Five samples of spot-disseminated molybdenite yield model ages varying from 139.9±2.3 Ma to 141.5±3.2 Ma, with an isochron age of 140.3±3.4 Ma (MSWD=0.082), and a weighted average of 140.10±1.80 Ma. The isochron age and weighted average model age are consistent with one another, implying that molybdenum mineralization in Hongling deposit occurred in Late Jurassic. A film-like molybdenite sample yielded a model age of 143.7±3.6 Ma, representing the initial stage of lead-zinc mineralization. The Re-187Os contents of the film-like molybdenite are higher than that of spot-disseminated molybdeniteby one order of magnitude, which hints that they have different origins and there are two phases of molybdenum mineralization. The characteristics of Re content of the 6 molybdenite samples suggest that the ore-forming elements had a shallow source, and was mainly derived from the crust. The extremely low content of Re might be du to the low Re content within its parent magma as well as its paragenetic mineral assemblage. Combined with the results of previous study, it is concluded that (a) both rock- and ore-forming materials of Hongling deposit came from hyperplasia crust; and (b) the deposit formed in a dynamical environment of continental crust extension post Mongolia-Okhotsk collisional orogeny.
Huanggang tin-iron deposit. Inner Mongolia, is an important deposit of the South Daxinganling metallogenic belt LA-ICP-MS zircon U-Pb dating results show that the K-feldspar granite and granite-porphyry in the Huanggang rocks were formed at 136.7 ± 1.1 Ma and 136.8 ±0.57Ma, respectively. The Huanggang granites are characterized by SiO 2 content (66.81%∼77.39% ) , Al 2O 3content ( 11.33%∼14.54%) , and significant depletion of magnesium, high ALK (5.65% ∼10.67%) , the K 2O/Na 2O values format a range of 0.32 to 10.53, averaging 2.78. The chondrite-nomalized REE pattern shows LREE enrichment, strong negative Eu anomalies, and δEu at 0.03 to 0.20. The high field strength elements such as Zr, Hf and lithophile elements such as Rb, U and Th are enriched, whereas the elements P, Ti, Ba and Sr are significantly depleted and their have similar Y/Nb values ( > 1.2) to those of oceanic island basalts. These features are coincident with the typical A1 within-plate anorogenic granite. Its genesis might be ascribed to the underplating of the mantle-derived magma which caused younger crust partial melting to form granitic magma within the lithosphère extension environment, and its magma source are related to the crust-mantle mixed remelting.
The Middle-Lower Yangtze River Valley metallogenic belt is one of the most important metallogenic belts in China, which experienced a long history of mining exploration and utilization. Many geologists have carried out researchs on this area since the 1920s and have published hundreds of scientific papers and more than 50 books. According to statistics, there are 888 scientific papers published in Chinese Journals focusing on the Middle-Lower Yangtze River Valley metallogenic belt from 1959 to 2012, and 185 SCI papers were published from 1990 to 2012. The research about ore deposits and mineralization is nearly occupying half of the total number of the published papers. The amount of published papers about the Tongling ore district in the belt is the highest. The number of published papers about Middle-Lower Yangtze River Valley metallogenic belt formed two peaks in the early 1990s and 2010 ∼2012 and still exhibit increasing trend, which shows that the Middle-Lower Yangtze River Valley metallogenic belt has been one of the hotspots for geological research in recent years. The researchers focus on four fields: (1) Mesozoic tectonic evolution and dynamic background of magmatism and mineralization, (2) magmatism and plutonic activity, (3) ore-forming system and evolution, (4) metallogenic potential. This edition contains 26 papers generally reflect the latest research progress of the Middle-Lower Yangtze River Valley metallogenic belt and its adjacent areas. Those papers report many new geological and petrological observations, elemental and isotopic geochemical data and high-precision U-Pb zircon age data etc. These documents offer important evidences for further understanding of the origin and evolvement of the Middle-Lower Yangtze River Valley metallogenic belt and also have important significance on prospecting in the area.
The southern Daxing'anling, where tens polymetallic deposits lie, is one of important metallogenic zones in Northern area of China. Lead and sulfur isotope geochemistry is helpful for determining the sources of ore-forming materials. On the basis of predecessors' research, sulfur and lead isotopic characteristics of sulfides from some polymetallic deposits have been studied in this paper. The δ 34S values of sphalerite, galena, arsenopyrite, chalcopyrite, and molybdenite rang from -6‰ to +4‰, with mean value of zero. The δ 34S values of most sulfides range from 0 to 2 ‰ with a pronounced tower effect, and without significant enrichment in the light sulfur and heavy sulfur, which suggests that the sulfur source is single and dominated by magmatic sulfur. Ratio values of lead isotope in both sulfides and related rocks range from 18.13 to 18.74 for 206Pb/ 204Pb, 15.38 to 15.68 for 207Pb/ 204Pb, and 37.1 to 38.93 for 208Pb/ 204Pb. Their mean values are 18.38, 15.54 and 38.09, respectively. Lead isotopic compositions also show obvious differences between the western and the eastern part in the southern Daxing'anling. In the lead isotopic compositions diagram, samples from polymetallic deposits in the western part are scattered nearby the evolution curve orogenic belts, while those from deposits in the eastern part are nearby curves of the orogenic belt and the upper mantle.
Hongling lead-zinc deposit is one of the representative large deposits in southeastern Inner Mongolia. Presently, there's very little research on geochemical characteristics and evolution of ore-form fluids, and ore genesis. The fluid inclusions are systemly researched in this paper, The results show that there are three types of primary fluid inclusions in garnet of garnet-skarn stage (I) including halite-bearing three-phase, aqueous two-phase as well as vapor-rich two-phase; there are two types of primary fluid inclusions in quartz of stage (II) including aqueous two-phase as well as vapor-rich two-phase. It is found in our microthermometric study that the ore-forming fluid is of high temperature, high salinity and immiscible NaCl-H2O type solutions and the boiling process plays important role in the precipitation of Pb, Zn, and Cu. Quartz of mineralization stage III to IV of quartz-sulfide epochs contains only aqueous two-phase of fluid inclusions. The homogenization temperature of this type of fluid inclusions is obviously lower than that of skarn epoch, while the salinity does not obviously change. The homogenization temperatures of fluid inclusions show a rising trend with salinities displaying a dropping trend of stage IV, and it may be caused by adding of high temperature, low salinity type fluid. The dropping of homogenization temperatures and salinities of ore-forming fluids from mineralization stages V to VI suggests that meteoric water continuously joining into the ore-forming fluid. Overall, the ore-forming fluids of quartz-sulfide epoch is of medium-low temperature and low salinity NaCl-H2O type solutions. C, H, O isotope study of fluid inclusions shows that the ore-forming fluids of skarn epoch mainly came from magmatic water and that of quartz-sulfide epoch came from mixed magmatic water and meteoric water, whereas at the latest stage of mineralization, the ore-forming fluids mainly came from meteoric water. The study of S, Pb isotopes implies that the ore-forming materials posed a deep source feature.
Coupled H- and O-isotope studies of natural waters and hydrous phases can constrain the sources of water, which can elucidate geological processes (both at high and low T) related to water-mineral reactions throughout the crust. Certain waters, such as sea-water or meteoric water, have well-characterized isotopic compositions, whereas some high T formation waters of magmatic or metamorphic origin, do not. The latter are usually represented by a poorly defined field or 'box' that may partly overlap other fields. Because of this, additional geological data and arguments may be necessary to arrive at a sound interpretation of a given system. It is also evident that the areas of uncertainty are numerous and increase greatly going back in time, particularly in the Precambrian where the number of detailed multi-isotope studies is extremely limited. Inevitably, the interpretation of ancient systems involving aqueous fluids of sea-water or meteoric origin is influenced by our more detailed knowledge of the ocean-water-meteoric system.-J.M.H.
The Da Higgan Mts. is an impotent polymetallic mineralized zone in the north part of China. This paper discusses the metallogenetic system of the Da Higgan Mts. according to the source of its metallogenic materials and its tectonic settings. Sr-Nd-O-Pb isotopic researches show a deep source of the metallogenic materials in the Da Higgan Mts. , and studies on composition of the Late Mesozoic crust-mantle migmatitic granitic rocks in the Da Higgan Mts. and their structural environment indicate that they are A-type granitic rocks formed in an intraplate and non-orogenic extensional environment. Understanding of the Mesozoic metallgenetic characteristics of the Da Higgan Mts. is deepened through comparison with Nanling granitic rocks and its mineralization. The deep structures of the Da Higgan Mts. further reveal its tectonic background of lithogenesis and mineralization.
The Budunhua Cu deposit is a porphyry-hydrothermal vein type composite deposit in the middle south part of the Da Hinggan Mountains. The deposit consists of the southern Jinjiling porphyry Cu ore block and northern Kongqueshan hydrothermal vein-type Cu ore block. Based on a detailed analysis of geological characteristics and a study of hydrogen, oxygen, sulfur, and lead isotopes in hydrothermal minerals, this paper has discussed the origin of ore -forming fluid and materials and genesis of the Budunhua deposit. Hydrogen and oxygen isotope analyses indicate that the ore -forming fluid in the early ore -forming stage in Jinjiling and Kongqueshan ore blocks was mainly magmatic water, whereas that in the late ore-formaing stage was probably a mixed fluid of magmatic and meteoric water. Sulfur isotope analyses show that the Jinjiling ore block is relatively rich in 34S, with sulfur isotope composition of ore-forming fluid being +2.54∼+60%o, while the Kongqueshan ore block is relatively depleted in 34S, with sulfur isotope composition of ore-forming fluid being -1.84∼-1.71%o. The sulfur isotope composition of the two ore blocks suggest a deep-seated source, and the lead isotope results display crust-mantle mixing characteristics closely related to magmatism. With the regional geological evolution history of the middle -south part of the Da Hinggan Mountains as a premise, the mineralization of the Jinjiling and the Kongqueshan Cu ore blocks in the Budunhua Cu deposit should be mainly related to fluid mixing which led to the precipitation of metal sulfides.
The Baiyinnuo'er deposit is the largest Zn-Pb deposit in northern China, which is related to the Yanshanian magmatic intrusions emplaced in limestone of the Early Permian Huanggangliang Formation. The hydrothermal evolution can be generally divided into three stages. The pre-ore stage (P-stage), with dominant mineral assemblages of pre-ore garnet and pyroxene, is characterized by coexisting brine and vapor-rich fluid inclusions, indicating an immiscible condition and, using the homogenization temperatures (∼470°C) and salinities of the brine (∼44% NaCleqv), trapping pressure can hence be estimated to be ∼400 bars, equivalent to a depth of ∼ 1. 5km. In some stockwork quartz, halite-saturated inclusions homogenized by halite dissolution are abundant with minimum trapping pressures ranging from several hundred bars to 3000 bars, interpreted as the result of over-pressure caused by the continued exsolving fluid from the magma chamber. In the syn-ore stage (S-stage), hydrous minerals and sulfides are widespread, and liquid-rich inclusions coexisted with vapor-rich inclusions are observed in sphalerite as well as quartz and calcite. An average trapping pressure of ∼ 150 bars, which is estimated by the average homogenization temperature of ∼350°C and salinity of ∼ 7% NaCleqv, corresponds to a formation depth of 1. 5km, the same as the pre-ore stage. The post-ore stage (L-stage) is characterized by calcite (-quartz-fluorite) veinlets with little sulfides. In this stage, CaCl 2-bearing fluid is recognized and Ca/Na increases dramatically as the temperature decreases, suggesting a non-magmatic origin and most likely from the sedimentary limestone. Fluid inclusion studies show that the mineralization-related fluid is of magma origin. Prograde minerals formed during the P-stage fluid immiscibility while the sulfide deposition occurred during the S-stage fluid boiling. The fluids responsible for P- and S-stage evolved through different cooling paths.
Most large skarn deposits are zoned in both space and time relative to associated intrusions. Zonation occurs on scales from kilometers to micrometers, and reflects infiltrative fluid flow, wallrock reaction, temperature variations, and fluid mixing. The most spectacular examples of skarn zonation usually occur at the skarn-marble contact, where transitions between monomineralic bands can be knife sharp. Other small-scale examples occur in zoned veins and individual mineral crystals. Although, visually striking and scientifically interesting, in mineral exploration these small-scale variations are less useful than deposit- or district-scale zonation. In most skarn systems there is a general zonation pattern of proximal garnet, distal pyroxene, and vesuvianite (or a pyroxenoid such as wollastonite, bustamite, or rhodonite) at the marble front. As well, individual skarn minerals may display systematic color or compositional variations within the larger zonation pattern. Such patterns are reviewed for 14 well-studied examples of Cu, W, Sn, Au, and Zn-Pb skarns. In addition, many deposits have endoskarn or other alteration of the associated intrusion, and recrystallization or other subtle changes have occurred in the surrounding wallrocks. Copper skarns, such as Mines Gaspe in Quebec and Big Gossan in Irian Jaya, have high ratios of garnet:pyroxene and are zoned outward from the intrusion, to garnet, to pyroxene, to massive-sulfide replacement and vein deposits. Garnets in Cu skarn are Fe-rich and change from dark red-brown near the intrusive contact to paler brown, green, or yellow in distal locations. Pyroxenes in Cu skarns are pale and diopsidic near the intrusion, and become darker and more Fe- and Mn-rich away from the intrusion. Tungsten skarns, such as Salau and Costabonne in France and Pine Creek and Garnet Dike in California, have intermediate ratios of garnet:pyroxene, are more extensive vertically and along strike than perpendicular to the intrusive contact, and have zonation patterns commonly complicated by overprinting of metamorphic lithologies. In W skarns, garnet is commonly subcalcic and the pyroxene is Fe-rich, reflecting particularly reducing wallrocks or great depth of formation. Tin skarns, such as Dachang in China and Moina in Australia, also can have subcalcic garnet and Fe-rich pyroxene, but this reduced mineral assemblage typically is due to an association with reduced S-type granites. Tin skarns differ from most other skarn types in having a late greisen stage that may replace earlier Sn-bearing calc-silicate minerals, thus liberating Sn to form cassiterite. Many high-grade Au skarns, such as Hedley in British Columbia and Fortitude in Nevada, have low ratios of garnet:pyroxene and are associated both with reduced plutons and reduced wallrocks. Gold-rich zones occur in Fe-rich, pyroxene-dominant, distal skarn. Zn-Pb skarns, such as the Yeonhwa-Ulchin district in Korea and Groundhog in New Mexico, have low ratios of garnet:pyroxene and generally form distal to associated intrusions. These skarns also are zoned from proximal garnet to distal pyroxene and pyroxenoid (bustamite-rhodonite), with significant zones of massive sulfides within and beyond skarn. Manganese enrichment of most mineral phases, particularly pyroxene, is characteristic of distal zones. Fundamental controls on skarn zonation include temperature, depth of formation, composition and oxidation state of associated plutons and wallrocks, and tectonic setting. Most W skarns form at relatively great depth, 5 km to 20 km, with extensive high-temperature metamorphic and metasomatic mineral assemblages. In contrast, most other skarn types are relatively shallow, <10 km and mostly <5 km, with limited, lower temperature metamorphic aureoles. Differences in oxidation state correlate well with different skarn zonation patterns, particularly garnet:pyroxene ratios and compositions, and can be used in both classification of and exploration for skarn deposits. Zonation models, especially where quantified, can be used predictively in exploration both for known and blind targets.
The Bilihe gold deposit is located in the eastern section of the Ondor Sum–Yanji Suture at the southern margin of the Xing’an–Mongolian Orogenic Belt (XMOB) and the northern margin of the North China Craton (NCC), central Inner Mongolia. The magmatic rocks in the ore district are generally high-K calc-alkaline, enriched in LREE, Zr, and Hf, and depleted in HREE, Nb, Ta, and P. The magmatic evolution sequences are norite gabbro → granodiorite porphyry → granite or norite gabbro → andesite → dacite porphyry → granodiorite, which show a trend of decreasing TiO2, FeO, MgO, CaO, and P2O5 with increasing SiO2. In the Bilihe ore district, hydrothermal processes were coeval with granitic magmatism for a period of ~ 17 Myr (272–255 Ma). The ages of the granite, granodiorite porphyry, granodiorite, and dacite porphyry are 271.5–264.1 Ma, 269.8–255.8 Ma, 268.3 Ma, and 268.6–259.4 Ma, respectively. The magmatic rocks contain magmatic, hydrothermal, and magmatic–hydrothermal zircons. The magmatic zircons have δCe > 4, La < 3 ppm, and SmN/LaN > 2.5; the hydrothermal zircons have δCe < 4, La > 3 ppm, and SmN/LaN < 2.5. The Nb/Ta and Zr/Hf ratios of granodiorite are 12.7–14.99 and 40.2–46.56, respectively. The Zr/Hf ratios successively increase in the sequence of granite (27.4–29.02) → granodiorite porphyry (29.19–32.18) → dacite porphyry (33.54–38.5) → norite gabbro (36.75–38.37), and their Nb/Ta ratios are 9.09–12.38. Zircons in granodiorite yield ε Hf (t) values of –0.29 to –56 (n = 13) and 2.07–7.62 (n = 5), and they give a Hf two-stage model age (tDM2) of 807–4765 Ma. The ε Hf (t) values of the zircons in granite, granodiorite porphyry, and dacite porphyry are –0.46 to 8.03, 3.17 to 10.32, and –0.78 to 6.58, respectively, and their Hf tDM2 ages are 787–1324 Ma, 638–1091 Ma, and 868–1343 Ma, respectively. Dehydration partial melting of subducted oceanic crust resulted in the formation of dacite porphyry; partial melting of depleted mantle resulted in the formation of norite gabbro; mixing of depleted mantle and lower crust resulted in the formation of granodiorite porphyry; partial melting of lower crust resulted in the formation of granite; and mixing of lower crust and old upper crust resulted in the formation of granodiorite. Magmatic rocks in the ore district with ages of 272–255 Ma were formed during the late stages of closure of the Paleoasian Ocean; i.e., during the transformation from a collisional to extensional setting.
This paper describes the basic stages of skarn formation and the main causes of variation from the general evolutionary model. Seven major classes of skarn deposits (Fe, W, Au, Cu, Zn, Mo and Sn) are briefly described, and relevant geological and geochemical features of important examples are summarized in a comprehensive table. The important geochemical and geophysical parameters of skarn deposits are discussed, followed by a summary of important petrologic and tectonic constraints on skarn formation. Finally, exploration models are presented for several major skarn types. -from Author
The Gaogangshan Mo deposit, located in the northern part of the Lesser Xing'an Range (the eastern part of the Xing'an–Mongolia Orogenic Belt), is one of the newly discovered Mo deposits in northeast China. Ore bodies occur in the granite and are generally in vein and stockwork forms. Major metallic minerals in the ore include pyrite and molybdenite. The styles of mineralization are disseminated, veinlet–disseminated, and veinlet. The major types of wall–rock alteration are silicification–potassic alteration, phyllic alteration and propylitization. Fluid inclusion analyses indicate that the ore-forming fluid during the major mineralization stage is an H2O–NaCl–CO2 system, with wide homogenization temperature and salinity ranges. The abundant CO2–rich and coexisting halite–bearing fluid inclusion assemblages in the main stage of mineralization highlight the significance of intensive fluid boiling for porphyry Mo mineralization. Comprehensive study of the ore-forming conditions, geological features of the deposit, micro-thermometric analysis of fluid inclusions and comparison of the Gaogangshan deposit with other typical porphyry deposits leads to the conclusion that the deposit is a porphyry type. We obtained a weighted mean age of the molybdenite deposit at Gaogangshan of 250.7 ± 1.8 Ma. The isotopic dating results indicate that the Gaogangshan deposit was formed in the Permo–Triassic, which is the earliest Mo–only deposit in northeast China. The formation of the Gaogangshan Mo deposit may be related to the extension and break–up of the Songnen Block and Jiamusi Block in the Permo–Triassic.
The Baiyinnuo'er zinc-lead deposit (32.74 Mt at 5.44% Zn, 2.02% Pb, and 31.36 g/t Ag), located in the south segment of the Great Xing'an Range, is the largest Zn-Pb deposit in northern China. Skarn and orebodies mainly occur between the different units of the Huanggangliang Formation, or within the contact zone between the intrusions and Permian marble. Several phases of igneous rocks exposed within the mining areas, and among them the Yanshanian plutonic rocks, which intruded into limestone of the early Permian Huanggangliang Formation, are interpreted to be the source of ore, since their Pb isotope compositions (206Pb/204Pb = 18.25-18.35, 207Pb/204Pb = 15.50-15.56, and 208Pb/ 204Pb = 38.14-38.32) are highly consistent with the sulfides, including sphalerite, galena, and chalcopyrite (206Pb/ 204Pb = 18.23-18.37, 207Pb/204Pb = 15.47-15.62, and 208Pb/204Pb = 37.93-38.44). Sulfur isotope values of the sulfides give a narrow δ34S interval of -6.1 to -4.6‰ (mean = -5.4‰, n = 15), suggesting the ore-forming fluid is of magmatic origin. Three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observation, which are the preore stage (garnet-clinpyroxene-wollastonite-magnetite ± sulfides), the synore stage (sulfides-epidote-quartz-calcite ± garnet), and the postore stage (calcite-chlorite-quartz-fluorite). Several fluid evolution episodes can be inferred from microthermometric results at the Baiyinnuo'er Zn-Pb deposit: 1. Immiscibility: Preore-stage coexistence of halite-bearing brine inclusions (S1-type, ∼44 wt % NaCl equiv) and vapor-rich fluid inclusions (V-type) sharing the same homogenization temperatures (∼470°C) confirms that fluid unmixing occurred under lithostatic pressures of ∼400 bars (∼1.5 km), and the brine is considered to account for most prograde skarn minerals (e.g., clinopyroxene). 2. Overpressure trapping: Preore-stage brine inclusions homogenized by halite dissolution (S2-type) postdated the immiscible assemblages. This type of inclusions is characterized by high but variable (minimum) trapping pressures (150-3,000 bars) relative to S1-type inclusions and can be explained as a result of entrapment under overpressuring condition. 3. Boiling: The presence of both vapor and liquid inclusions (i.e., V- and L-type) in the same assemblages within synore-stage quartz, calcite, and sphalerite indicates the occurrence of fluid boiling (∼350°C), at hydrostatic pressures of ∼150 bars, and depth of ∼1.5 km), which resulted in large-scale mineralization in the Baiyinnuo'er Zn-Pb deposit. 4. Mixing with external fluids: Fluid inclusions scattered within postore-stage calcite or secondary trails in synore-stage minerals show low homogenization temperatures (<260°C) and both decreasing (for L-type) and increasing (for CaCl2-bearing inclusions, i.e., Lc-type) trends for salinities as homogenization temperatures decrease, implying addition of both meteoric water (low-temperature, low-salinity) and basinal brines (lowtemperature, Ca-rich), respectively. Systematic fluid inclusion studies also indicate that the mineralization-related fluid is of magmatic origin. Prograde minerals formed during the preore-stage fluid immiscibility while sulfides deposition occurred during the synore-stage fluid boiling. Mixing with external fluids began as the hydrothermal system cooled to <300°C, when the main metal precipitation process had ended.
The Shapinggou porphyry Mo deposit, one of the largest Mo deposits in Asia, is located in the Dabie Orogen, Central China. Hydrothermal alteration and mineralization at Shapinggou can be divided into four stages, i.e., stage 1 ore-barren quartz veins with intense silicification, followed by stage 2 quartz-molybdenite veins associated with potassic alteration, stage 3 quartz-polymetallic sulfide veins related to phyllic alteration, and stage 4 ore-barren quartz +/- calcite +/- pyrite veins with weak propylitization. Hydrothermal quartz mainly contains three types of fluid inclusions, namely, two-phase liquid-rich (type I), two- or three-phase gas-rich CO2-bearing (type II) and halite-bearing (type III) inclusions. The last two types of fluid inclusions are absent in stages 1 and 4. Type I inclusions in the silicic zone (stage 1) display homogenization temperatures of 340 to 550 degrees C, with salinities of 7.9-16.9 wt.% NaCl equivalent. Type II and coexisting type III inclusions in the potassic zone (stage 2), which hosts the main Mo orebodies, have homogenization temperatures of 240-440 degrees C and 240-450 degrees C, with salinities of 34.1-50.9 and 0.1-7.4 wt.% NaCI equivalent, respectively. Type II and coexisting type III inclusions in the phyllic zone (stage 3) display homogenization temperatures of 250-345 degrees C and 220-315 degrees C, with salinities of 02-65 and 32.9-39.3 wt.% NaCI equivalent, respectively. Type I inclusions in the propylitization zone (stage 4) display homogenization temperatures of 170 to 330 degrees C, with salinities lower than 6.5 wt.% NaCI equivalent. The abundant CO2-rich and coexisting halite-bearing fluid inclusion assemblages in the potassic and phyllic zones highlight the significance of intensive fluid boiling of a NaCl-CO2-H2O system in deep environments (up to 2.3 kbar) for giant porphyry Mo mineralization. Hydrogen and oxygen isotopic compositions indicate that ore-fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials at Shapinggou are magmatic in origin. Re-Os dating of molybdenite gives a well-defined Re-187/Os-187 isochron with an age of 112.7 +/- 1.8 Ma, suggesting a post-collisional setting.
Mineral deposits are typically tied to plate margin processes, such as accretion or rifting. However, some major deposits occur in plate interiors, e.g., deposits in the southern Great Xing'an Range, lacking a clear association with the supercontinent cycle. Intrusive activity in the southern Great Xing'an Range peaked in late Mesozoic (i.e., 155-120 Ma), simultaneously with large-scale mineralization in this area. In addition, the late Mesozoic granitoids show initial Nd and Hf isotopic signatures of depleted mantle, possibly newly underplated basaltic materials, with variable contamination from older crust, and with model ages younger than 1.0 Ga. Fluid inclusion waters extracted from ore minerals (pyrite, galena, sphalerite, and chalcopyrite) associated with the late Mesozoic mineralization have elevated 3He/4He ratios, indicating a contribution of mantle-derived helium. Stable isotopes of fluid inclusion waters (hydrogen and oxygen) and of sulfide minerals (sulfur) confirm a magmatic source for these components. Lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material. Thus, the southern Great Xing'an Range is best described as a typical, late Mesozoic, intracontinental metallogenic belt related to magmatism with a significant mantle contribution. The magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break-off of the southerly-dipping Mongol-Okhotsk oceanic slab at depth during closure of the Mongol-Okhotsk Ocean, which also restricted the westward movement of the Paleo-Pacific oceanic plate. This interplay between plate-tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings.
The southern Great Xing'an Range is one of the most important metallogenic belts in northern China, and contains numerous Pb–Zn–Ag–Cu–Sn–Fe–Mo deposits. The Huanggang iron–tin polymetallic skarn deposit is located in the Sn-polymetallic metallogenic sub-belt. Skarns and iron orebodies occur as lenses along the contact between granite plutons and the Lower Permian Huanggangliang Formation marble or Dashizhai Formation andesite. Field evidence and petrographic observations indicate that the three stages of hydrothermal activity, i.e., skarn, oxide and sulfide stages, all contributed to the formation of the Huanggang deposit.
The skarn stage is characterized by the formation of garnet and pyroxene, and high-temperature, hypersaline hydrothermal fluids with isotopic compositions that are similar to those of typical magmatic fluids. These fluids most likely were generated by the separation of brine from a silicate melt instead of being a product of aqueous fluid immiscibility. The iron oxide stage coincides with the replacement of garnet and pyroxene by amphibole, chlorite, quartz and magnetite. The hydrothermal fluids of this stage are represented by L-type fluid inclusions that coexist with V-type inclusions with anomalously low δD values (approximately − 100 to − 116‰). The decrease in ore fluid δ¹⁸OH2O values with time coincides with marked decreases in the fluid salinity and temperature. Based on the fluid inclusion and stable isotopic data, the ore fluid evolved by boiling of the magmatic brine. The sulfide stage is characterized by the development of sphalerite, chalcopyrite, fluorite, and calcite veins, and these veins cut across the skarns and orebodies. The fluids during this stage are represented by inclusions with a variable but continuous sequence of salinities, mainly low-salinity inclusions. These fluids yield the lowest δ¹⁸OH2O values and moderate δD values ( − 1.6 to − 2.8‰ and − 101 to − 104‰, respectively). The data indicate that the sulfide stage fluids originated from the mixing of residual oxide-stage fluids with various amounts of meteoric water. Boiling occurred during this stage at low temperatures.
The sulfur isotope (δ³⁴S) values of the sulfides are in a narrow range of − 6.70 to 4.50‰ (mean = − 1.01‰), and the oxygen isotope (δ¹⁸O) values of the magnetite are in a narrow range of 0.1 to 3.4‰. Both of these sets of values suggest that the ore-forming fluid is of magmatic origin. The lead isotope compositions of the ore (²⁰⁶Pb/²⁰⁴Pb = 18.252–18.345, ²⁰⁷Pb/²⁰⁴Pb = 15.511–15.607, and ²⁰⁸Pb/²⁰⁴Pb = 38.071–38.388) are consistent with those of K-feldspar granites (²⁰⁶Pb/²⁰⁴Pb = 18.183–18.495, ²⁰⁷Pb/²⁰⁴Pb = 15.448–15.602, ²⁰⁸Pb/²⁰⁴Pb = 37.877–38.325), but significantly differ from those of Permian marble (²⁰⁶Pb/²⁰⁴Pb = 18.367–18.449, ²⁰⁷Pb/²⁰⁴Pb = 15.676–15.695, ²⁰⁸Pb/²⁰⁴Pb = 38.469–38.465), which also suggests that the ore-forming fluid is of magmatic origin.
The Nuri Cu‐W‐Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu‐Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz‐polymetallic sulfide stage and quartz‐carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two‐phase aqueous inclusions, daughter mineral‐bearing multiphase inclusions, CO2‐rich inclusions and single‐phase inclusions. The homogenization temperature of the fluid inclusions are 280°C–386°C (skarn stage), 200°C–340°C (oxide stage), 140°C–375°C (quartz‐polymetallic sulfide stage) and 160°C–280°C (quartz‐carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz‐carbonate stage. The salinity of the corresponding stages are 2.9%–49.7 wt% (NaCl) equiv., 2.1%–7.2 wt% (NaCl) equiv., 2.6%–55.8 wt% (NaCl) equiv. and 1.2%–15.3 wt% (NaCl) equiv., respectively. The analyses of CO2‐rich inclusions suggest that the ore‐forming pressures are 22.1 M Pa–50.4 M Pa, corresponding to the depth of 0.9 km–2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H2O, with some CO2 and very little CH4, N2, etc. δD values of garnet are between −114.4‰ and −108.7‰ and δ18OH2O between 5.9‰ and 6.7‰; δD of scheelite range from −103.2‰ to −101.29‰ and δ18OH2O values between 2.17‰ and 4.09‰; δD of quartz between −110.2‰ and −92.5‰ and δ18OH2O between −3.5‰ and 4.3‰. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The δ34S values of sulfides, concentrated in a rage between −0.32‰ to 2.5‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen‐oxygen and sulfur isotopes data, show that the ore‐forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO2 or other gases. During the reaction, the ore‐forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore‐forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO2 from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.
a b s t r a c t North-eastern China and surrounding regions host some of the best examples of Phanerozoic juvenile crust on the globe. However, the Mesozoic tectonic setting and geodynamic processes in this region remain debated. Here we attempt a systematic analysis of the spatio-temporal distribution patterns of ore deposits in NE China and surrounding regions to constrain the geodynamic milieu. From an evalua-tion of the available geochronological data, we identify five distinct stages of ore formation: magmatism and associated mineralisation occurred during in a post-collisional tectonic setting involving the closure of the Paleo-Asian Ocean. The Early-Mid Jurassic (190–165 Ma) events are related to the subduction of the Paleo-Pacific Ocean in the eastern Asian continental margin, whereas in the Erguna block, these are associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale con-tinental extension occurred in NE China and surrounding regions. However, the Late Jurassic magmatism and mineralisation events in these areas evolved in a post-orogenic extensional environment of the Mon-gol–Okhotsk Ocean subduction system. The early stage of the Early Cretaceous events occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. The widespread extension ceased during the late phase of Early Cretaceous (115–100 Ma), follow-ing the rapid tectonic changes resulting from the Paleo-Pacific Oceanic plate reconfiguration.
The fluid inclusion and H–O isotope studies have provided the evidences for the source of ore-forming fluids, and helped to recognize two types of immiscibility and their relationships with mineralization. Hydrogen and oxygen isotopic geochemistry shows that the earlier ore-forming fluids during the anhydrous skarn stage (I) and the hydrous skarn-magnetite stage (II) were mainly derived from magmatic water, while the later fluids during the quartz-sulfide stage (III) and the carbonate stage (IV) were mainly from magmatic water mixed with small amounts of meteoric water. Various types of fluid inclusions, including abundant vapor- or liquid-rich two-phase aqueous inclusions, daughter minerals-bearing multiphase inclusions, CO2–H2O inclusions, and less abundant liquid inclusions, vapor inclusions and melt inclusions, are present in hydrothermal minerals of different stages. The liquid–vapor fluid inclusions are mainly composed of H2O, with significant amounts of CO2 and a small amount of CH4. In the opaque-bearing fluid inclusions, the hematite and fahlore (tetrahedrite) were identified. The homogenization temperature of the aqueous fluid inclusions decreases from Stage I (520–410°C), through Stage II (430–340°C) and III (250–190°C), to Stage IV (190–130°C). The coexistence of melt inclusions with simultaneously trapped vapor- or liquid-rich two-phase aqueous inclusions and daughter minerals-bearing multiphase inclusions in garnet, diopside and epidote of Stages I and II suggests an immiscibility between silicate melt and hydrothermal fluid. It is an effective mechanism on scavenging and transporting ore-forming components from magmas. The aqueous fluid inclusions with various vapor/liquid ratios (from 65%) commonly coexist with simultaneously trapped liquid inclusions, vapor inclusions, daughter minerals-bearing multiphase inclusions and CO2–H2O inclusions in the quartz of Stage III, and the different kinds of the fluid inclusions have similar homogenization temperatures. This indicates that the boiling – another kind of immiscibility, widely took place during Stage III. It resulted in the precipitation and enrichment of gold, copper and iron.
Exhaustive investigations were launched for confirming the upper Permian host rocks of the Dajing Cu-Sn Deposit, probing into the possibility that Dajing is a Sedex type deposit during cosedimentation, complementing the deficiency of previous researches and going further into substantiating the role of the upper Permian strata in the control of ore distribution. After more than two years work, we reclassified the sedimentary facies in the Dajing area and its periphery as shallow fresh water lake and delta. Indicative sedimentary structures, such as ripple marks, rain marks, and mud cracks combined with contemporary fossils, were revealed. Having measured the flow directions, performed chemical comparison, and analyzed various sediments from sourceland in the Dajing area by XRF, we consequently redivided the strata into four sedimentary members, among which P2l1 and P2l2 were concluded as significant ore-hosted strata. The upper Permian basin was a lateral rift basin. The water and sediments in the basin are much deeper and thicker in the north than those in the south.
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation.