Metallogenic Period Research Articles

Multistage ore formation in the world’s largest REE-Nb-Fe deposit of Bayan Obo, North China Craton: New insights and implications

The Bayan Obo deposit in the northern margin of the North China Craton is a world-class REE-Nb-Fe deposit, the complex mineralization history of which remains unresolved. In this study, we employ SEM and Image J software combined with mineralogical data obtained by in-situ EDS and EPMA analyses to analyze petrographic images rapidly and to investigate the mineralogical assemblages of each type of rocks/ores from the Main Orebody in an attempt to understand the mineralization process and ore-formation mechanism of this deposit. We identify three metallogenic periods and six ore-forming stages based on the field occurrence of ores combined with published geochronological data. The Mesoproterozoic magmatic event comprises two stages, which were distinguished as the coarse-grained dolomite stage (stage 1) and the fine-grained dolomite stage (stage 2). Three stages were recognized in the Mesoproterozoic shear deformation-hydrothermal mineralization period, including the disseminated mineralization stage (stage 3), the banded mineralization stage (stage 4) and the massive mineralization stage (stage 5). The Paleozoic hydrothermal period involved the vein mineralization stage (stage 6). Based on detailed studies of the mineral assemblages and paragenesis, as well as the complex textures of the ores, we propose a model of the multi-stage metallogenic process as follows: (1) The REE minerals and rutile occurring as inclusions wrapped within magmatic idiomorphic dolomite grains indicate that the REE-Nb mineralization might have started during the magmatic period. (2) The Nb minerals, such as fergusonite and ilmenorutile, intergrown with REE minerals, such as monazite and bastnäsite, indicate that the Nb and REE were transported by the same ore-forming magma or fluid and precipitated during the same metallogenic process. (3) From the fine-grained dolomite stage to the massive mineralization stage (from stage 2 to stage 5), the mineral assemblages become more complex, with a gradual increase in the degree of hydrothermal alteration suggesting that more hydrothermal fluid was involved in the ore mineralization. (4) The complex mineralogical assemblages and textural relationships indicate multiple formation mechanisms for the REE-Nb-Fe minerals. We propose that the unusually large volume of REE-Nb-Fe resources in the Bayan Obo deposit was the result of combined magma and hydrothermal fluid activities in the Mesoproterozoic (from stage 1 to stage 5), whereas the fluids only caused reactivation of the ore materials previously deposited without the addition of exogenous materials in the Paleozoic stage (stage 6).

Genesis of Pyrite in Clastic Rocks of Deep Salt-Related Strata in the Simao Basin and Its Implication for Potash Mineralization: A Case Study of the Well MK-3

In depth of the Simao Basin (2390 to 2650 m depth interval), many gray mudstone or carbonate rocks are developed in the red salt-related strata, and pyrite crystals are found in the fissure and matrix. In this study, petrology, mineralogy, element geochemistry, and LA-MC-ICP-MS in situ sulfur isotope analysis were used to constrain the genesis of pyrite, and the influence of relevant geological activities on potash mineralization was discussed. The results show that: (1) In the upper part of the salt layer, particle size of the pyrite ranges from 50 to 300 μm. The crystal morphology is mainly pentagonal-dodecahedral and irregularly granular, with a small amount of cuboidal pyrite. In the interlayer between rock salt, particle size of the pyrite is from 50 to 100 μm, and the crystals are mainly octahedral. (2) The S/Fe value of pentagonal-dodecahedral pyrite is significantly greater than 2; the S/Fe value of octahedral and cubic pyrite is less than 2; and the S/Fe value of irregular granular pyrite is close to 2. (3) The δ34SV-CDT values of pyrite in the upper salt-related strata range from −15.65‰ to 11.81‰, and the average δ34SV-CDT values of all samples range from 0.79‰ to 8.20‰. The δ34SV-CDT values of pyrite interlayer between rock salt range from −15.02‰ to −6.36‰, with an average value of −10.66‰. The above results indicate that the pyrite in the upper part of the rock salt layer was formed in a medium-low temperature hydrothermal environment, and the ore-forming sulfur elements have hydrothermal sources, bacterial sulfate reduction (BSR) sources, and thermochemical sulfate reduction (TSR) contributions. The pyrite between the rock salt layers is of sedimentary origin, and the ore-forming sulfur element comes from BSR. At present, there is no evidence of the influence of hydrothermal activities on deep potash-rich salt bodies, and the influence on the Mengyejing potash deposit has continued since the metallogenic period.

Mineralization of the Liwu large-scale stratiform copper deposits in Sichuan Province, China: Constraints from fluid inclusions

The Liwu stratiform copper deposit is located in the NW Jianglang dome, western China. Current studies mainly focus on the genetic type and mineralization of this deposit. Detailed fluid inclusion characteristics of metallogenic period quartz veins were studied to reveal the ore-forming fluid features. Laser Raman analysis indicates that the ore-forming fluids is a H₂O-NaCl-CH₄ (-CO₂) system. Fluid inclusions microthermometry shows a homogenization temperature of 181–375°C and a salinity of 5.26%–16.99% for the disseminated-banded Cu-Zn mineralization; but a homogenization temperature of 142–343°C and a salinity of 5.41%–21.19% for the massive-veined Cu-Zn mineralization. These features suggest a medium–high temperature and a medium salinity for the ore-forming fluids. H-O isotopic data indicates that the ore-forming fluids were mainly from the metamorphic and magmatic water, plus minor formation water. And sulfur isotopic data indicates that sulfur was mainly derived from the formation and magmatic rocks. Metallogenesis of the disseminated-banded mineralization was mainly correlated with fluid mixing and water-rock reaction; whereas that of the massive-veined mineralization was mainly correlated with fluid boiling. The genetic type of the deposit is a medium-high temperature hydrothermal deposit related to magmatism and controlled by shear zones. This study is beneficial to understand the stratiform copper deposit.

Active ages of metallogenic structures in the Liangyan lead–zinc deposit, northwestern Guizhou: Constraints from geometric, kinematic, and sphalerite Rb-Sr dating analyses

More than ten lead–zinc deposits formed under the control of the Yadu-Mangdong fault (YMF) are known to have undergone multi-stage activity. However, ore control processes in such fault zones are poorly understood, such as in the Liangyan deposit in northwestern Guizhou. The internal geometrical structure, mineralization, alteration, tectonic stress, and kinematics of the YMF were investigated in three sections (1605, 1655, and 1720) of the Liangyan deposit. The ore-forming age (214.8 ± 4.3 Ma) was obtained by rubidium-strontium dating of sphalerite. The YMF is defined by double-fault cores and superimposed faults that indicate at least three stages of deformation since the mineralization period. The first stage is characterized by the ore-bearing dolomitization ancient fault core formed in the Indosinian period. The principal compressive stress direction was northwest to southeast (NW-SE). The second stage of Yanshanian was the tectonic breccia fault stage (new fault core). The principal compressive stress was northeast to southwest (NE-SW). The third stage was dominated by superposed faults that destroyed the new fault core in the Himalayan period. The principal compressive stress direction was east to west (E-W). In summary, we established a model of evolution for the YMF since the metallogenic period. In conclusion, based on the above research, we consider that the YMF turning point of the Liangyan deposit is prone to orebodies. Additionally, the prospecting target should be concentrated in the footwall (NW-trending) and hanging wall (NE-trending) of the Liangyan deposit YMF model.

A timeline of the Cenozoic tectonic–magmatic–metamorphic evolution and development of ore resources in the Himalayas

A large concentration of ore deposits (i.e., tungsten, tin, lithium, beryllium, lead, zinc, silver, antimony and gold) related to metamorphism and hydrothermal activity of granite developed in the Himalayas and are located in the southern part of the Qinghai‐Tibet Plateau. As one of the newest and largest examples in the world of continental–continental collisional orogenic belts, the Himalayas are optimal for studying the coupling of continental collisions with metamorphic, tectonic, magmatic events and ore resources. Although considerable research has been conducted in the Himalayas, the timing of various geological processes remains debated, which limits the understanding of the genesis of ore deposits. To better understand the influence of orogeny on the metallogenic process, this study comprehensively presents the time of activity of the above‐mentioned four Cenozoic geological processes in the Himalayas. This contribution focuses on the context of the timeline to determine the internal connections and discusses the interrelationships of the geological processes. This study argues that Cenozoic lower crust–mantle interactions deep within the Indian continental plate below the Himalayas controlled the tectonics, metamorphism, magmatism and mineralization in the middle–upper crust. Cenozoic magmatic rocks in the upper crust are the direct results of the main‐collisional and post‐collisional stages of the Indian and Eurasian continental blocks. Intense collisional shearing and metamorphism during the Eocene formed the Himalayan fault–fold Belt and orogenic gold deposits. The break‐off, detachment and slab tearing of the Indian lithosphere during the Miocene led to the extensional structure of the middle–upper crust. There is a close coupling relationship between the exhumation of the middle–lower crust and the formation of large‐scale leucogranites during the Miocene in the upper crust, which provides the geological context for the main metallogenic period during which tungsten, tin, lithium, beryllium, lead, zinc, silver, antimony and gold ore widely developed. With technological advancements, the analytical accuracy of geological ages has gradually improved. In the future, research on the temporal constraints of important geological activities should be strengthened, and then a comprehensive evolutionary model of multiple spheres of geological processes in the Himalayas should be established.

Genetic relationship between the Maoping Pb-Zn deposit and paleo-oil reservoir in the northern Yunnan-Guizhou depression: Evidence from bitumen trace elements and the in-situ sulfur isotope of pyrite associated with bitumen

The coexistence of numerous Mississippi Valley-type (MVT) Pb-Zn deposits and oil/gas reservoirs in the world demonstrates that a close genetic link between them. The northern Yunnan–Guizhou depression (NYGD) is a tectonic unit containing Pb–Zn deposits, paleo-oil reservoirs and shale gas. However, previous studies on the relationship between hydrocarbon accumulation and Pb–Zn mineralization have been ignored. The Maoping Pb–Zn deposit is a large-sized MVT deposit in the NYGD where a large amount of solid bitumen (i.e., a paleo-oil reservoir) occurs, and it is an ideal area to study the relationship between hydrocarbon accumulation and lead–zinc mineralization. In this paper, the bitumen and pyrite associated with bitumen from the Xujiazhai (discovered in this study) and Xiaocaoba paleo-oil reservoirs and the Maoping Pb–Zn deposit are researched. Geological observation has revealed that bitumen occurs in dissolution pores, fractures and intercrystalline pores in dolomite of the Upper Devonian and Carboniferous. The bitumen from Xujiazhai, Maoping and Xiaocaoba with high and similar Raman equivalent reflectance (RmcRo%) indicates they are in over-mature level and may be derived from the cracking of early-accumulated crude oils. The bitumen in the Xujiazhai paleo-oil reservoir and Maoping deposit has an abundant Pb and Zn content, indicating petroleum liquids may act as the transporting agents of metallogenic metal elements, carrying them to sites where mineralization may take place. The source rocks may have provided not only the oil for paleo-oil/gas reservoirs, but also a portion of ore metals for the Pb-Zn mineralization. The bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) processes were recorded by the pyrite in the paleo-oil reservoir, which was consistent with the mechanism of reduced sulfur formation in the Maoping deposit. In addition, the large negative (−27.7‰ to −5.7‰) and positive (.9‰ to 19.2‰) δ34S values of the pyrite associated with the bitumen in the paleo-oil reservoir were similar to those of the sulfide in the Maoping deposit. We believe that the formation and evolution of the paleo-oil reservoirs are closely related to the metallogenic process of the Maoping Pb–Zn deposit, and the sulfides in them have the same sulfur source and formation mechanism as reduced sulfur. BSR phenomena could occur in prior to migration of the hydrocarbons into the reservoir or low mature oil stage in paleo-oil reservoir; a small amount of H2SBSR was combined with metal ions in ancient oil reservoirs and deposits to form early subhedral, xenomorphic granular, fine-grained strawberry aggregate pyrite and/or gelatinous sphalerite. The paleo-gas reservoir formed by the evolution of the paleo-oil reservoir in the main metallogenic period potentially participated in the mineralization; that is, organic gas acted as a reducing agent and transformed SO42− in the upper Devonian Zaige Formation gypsum strata on the periphery of the Maoping lead–zinc mining area into H2STSR through TSR, providing reduced sulfur and creating the environmental conditions for mineralization. During or after the transformation of the paleo-oil reservoir to a paleo-gas reservoir, the decoupling of metals and organic complexes may have provided the ore metals for mineralization. Massive sulfide precipitation may have occurred during or after the paleo-oil reservoir cracked into the paleo-gas reservoir.

Fluid inclusion and stable isotope (H–O–S–Pb) constraints on the genesis of the Haxi gold deposit, west Junggar, China

The Haxi gold deposit located in the Hatu–Saertuohai metallogenic belt of the west Junggar region, China, is a newly discovered gold deposit with proven reserves of ∼10 tons of gold and an average grade of 6.70 g/t. Primarily, the deposit is hosted in the early Carboniferous Tailegula Formation, controlled by the NEE-trending Anqi fault. The gold ore bodies contain gold-bearing quartz veins and altered basalt. The ore mineral is dominated by abundant sulfides, such as pyrite, arsenopyrite, chalcopyrite, and a little gersdorffite. To date, three types of fluid inclusion in quartz veins have been identified: liquid–gas (V-type), CO2–H2O (C-type), and liquid–rich (L-type). The ore-forming fluids exhibit medium homogenization temperatures (Th) of 226 °C–325 °C with low salinities of 2.24–9.34 wt% NaCl equivalent and low densities from 0.72 to 0.88 g/cm3. The δD values range from −115.3‰ to −100.7‰, with an average value of −109.1‰; the δ18O values range from 11.3‰ to 12.2‰, with an average value of 11.8‰; and the δ34S values in sulfide range from 0.3‰ to 1.8‰, with an average of 1.2‰. The average values of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in sulfide are 18.059, 15.547, and 37.996, respectively. To summarize, the metallogenic fluids were derived not from a single source but from late magmatic–hydrothermal fluid mixed with paleo-atmospheric water; furthermore, the ore-forming materials principally originated from a crust–mantle mixed source. The Pb model age calculated using Hautman’s formula is 347–365 Ma, leading to the speculation that the metallogenic period may be Devonian–Carboniferous.

The fractures-controlled tin mineralization at the end of Late Cretaceous in the Songshan deposit, southwestern China: Constraints from U–Pb dating of zircon, garnet, and cassiterite

The Songshan tin deposit is located in the northern Lincang granitic batholith along the Lancangjiang tin belt, Western Yunnan, southwestern China. The ore bodies mainly occur as tourmaline-quartz veins with NNE- and/or NW-trending in the Triassic Pinghejie granitic pluton, and the schist of the Proterozoic Songshan Formation. The previous study suggested the tin mineralization in the Songshan deposit should occur in the Triassic, but no directed age data support it. This hinders the understanding of the genesis of the Songshan tin deposit, especially the tin mineralization in the Lancangjiang tin belt. Here, we report the zircons U-Pb ages of 222.7 ± 1.6 and 222.0 ± 2.4 Ma for the granodiorite, 215.1 ± 1.5 and 223.0 ± 2.0 Ma for the biotite monzogranite, and 222.3 ± 2.3 Ma for the alter granite from the Pinghejie granitic pluton. The monazite from the monzogranite yields a U-Pb age of 212.8 ± 1.9 Ma. We also obtain two garnet U-Pb ages of 215.1 ± 8.7 Ma and 213.5 ± 7.2 Ma from skarn, and two cassiterite U-Pb ages of 76.6 ± 1.5 Ma and 79.6 ± 3.6 Ma from tin ores. These data suggest that tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous, which is quite different from the ages of the Pinghejie granitic pluton emplaced and the formation of skarn. The zircon Hf isotopes (εHf(t) = –22 ∼ -12) and monazite Nd isotopes (εNd(t) = -13.04 ∼ -11.80) indicate that the Pinghejie granitic pluton was derived from the remelting of Paleoproterozoic crust. The paper concluded that the tin mineralization in the Songshan deposit occurred at the end of Late Cretaceous. It is another important metallogenic period in the Lancangjiang tin belt, which may be related to the subduction of the NeoTethys oceanic crust. The tin mineralization can not only occur in the magmatic arc, but also in the hinterland behind the magmatic arc.

Mineralogical and Geochemical Characteristics of Carbonates and Their Geological Significance to the Fuli Pb-Zn Deposit, Yunnan Province

Mississippi Valley-Type (MVT) deposits are among the main types of Pb-Zn deposits that feature carbonate minerals as the main gangue minerals; their formation runs through the entire metallogenic process of MVT deposits. Therefore, carbonate minerals contain rich information on metallogenic fluid evolution and are thus important prospecting indicators. The Fuli Pb-Zn deposit in eastern Yunnan is located in the southeast of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province, which is the biggest producer of zinc and lead in China and contains more than 400 deposits and over 20 million tons of Pb + Zn reserves. The ore occurs in the interlayer fracture zone of Middle Permian Yangxin Formation Dolomite, and the orebody shape is generally stratiform. The main metal-bearing minerals of this deposit are sphalerite, galena, and pyrite; the gangue minerals mainly comprise dolomite and calcite. Three mineralized stages are observed (the early metallogenic period, the main metallogenic period, and the late metallogenic period) according to the characteristics of stratigraphic output, the intercalated contact relationship of gangue minerals, and the alteration characteristics of the wall rock. To determine the source and properties of the ore-forming fluid and the ore-forming process of the Fuli Pb-Zn deposit, different stages of mineralogy and trace element geochemical characteristics of hydrothermal dolomite were systematically studied. The minerals were observed under microscope and subjected to in situ analysis by LA-ICP-MS and C–O isotope test. The δ18OSMOW value of the dolomite in the metallogenic period was between 13.29‰ and 20.55‰, and the δ13CPDB value was between −4.13‰ and 3.5‰. Dolomite of the metallogenic period mainly came from the dissolution of carbonate wall rocks, while C in the ore-forming fluid came from the wall rocks. A few dolomites showed a trend of depleting δ13CPDB and δ18OSMOW at the same time, implying the influence of sedimentary rock contamination in the mantle multiphase system. The lower δ18O was due to the exchange of O isotopes between the wall rocks and the depleted δ18O in ore-forming fluids. From the early to the later stage of mineralization, the ore-forming fluid changed from alkaline to neutral to weakly acidic due to a decrease in the oxygen fugacity and temperature of the fluid; this change resulted in the precipitation of sulfide and dolomite in the deposit. From the early to the late stages of mineralization, Fe and Mn showed a downward trend. Fe and Mn entered the alkaline environment of the carbonate minerals, while Fe and Mn were released into the acidic fluid, indicating that due to the metasomatism from strong to weak, their metallogenic environment evolved from alkaline to acidic. From the early to the late stage of mineralization, Sr showed an upward trend, which might indicate that the continuous reaction between the hydrothermal fluid and the wall rock continuously released Sr into the fluid. The Fe-Sr and Mn-Sr diagrams show that two kinds of fluid mixing occurred in the ore-forming process. The Fuli Pb-Zn deposit may have formed from mineral precipitation caused by the mixing of the metal-rich, oxidized acidic fluid and the sulfur-rich, reduced alkaline fluid. The results show that the Fuli Pb-Zn deposit belongs to MVT deposits.

Occurrence State and Properties of Gold Minerals from the Gold Deposits on the North China Platform

By studying both the microscopic physical and chemical typomorphic characteristics of gold minerals associated with representative gold deposits on the north-central margin of the North China Platform, this paper seeks to identify macroscopic metallogenic mechanisms of gold deposits. The majority of the gold minerals from the gold deposits are native gold with minor electrum and calaverite. The form and grain size of gold minerals from the representative gold deposits reflect the metallogenic properties of medium-deep and medium-high temperature deposits. The projected gold fineness of the Xiaoyingpan gold mine all falls in the medium-temperature area in the figure and tends to be in the high-temperature area, while that of the Zhangquanzhuang gold mine mostly falls in the middle-temperature area, showing the difference in the metallogenic conditions of the two deposits. Both Xiaoyingpan and Zhangquanzhuang gold deposits show the following rules: poor in Zn, Pb, Sb and Se, but rich in Cu, Fe without Mn, indicating that both deposits are of medium-deep origin. The three representative gold deposits all show high gold fineness characteristics, and the general rules are as follows: Dongping-type gold deposit (934.8-969.7) > Xiaoyingpan-type gold deposit (900.0) > Zhangquanzhuang type gold deposit (824.0), showing that the representative gold deposits were formed at higher temperature and deeper depth, and the gold in the ores inherited the characteristics of high gold fineness originating from the Archean metamorphic rock series, which implying that the metallogenic material originated from the ancient metamorphic rock series; the long metallogenic period and multiple metallogenic stages made gold fully transformed, purified and enriched. There are three main occurrence states of gold minerals in the study area, from primary to secondary, they are respectively inclusion gold, gold minerals between other mineral crystals and those filled in the fractures of other minerals.

RECOGNITION OF A 600-KM-LONG LATE TRIASSIC RARE METAL (Li-Rb-Be-Nb-Ta) PEGMATITE BELT IN THE WESTERN KUNLUN OROGENIC BELT, WESTERN CHINA

AbstractThe rising demand of strategic metals, especially lithium, necessitates discovery of new resources to meet the global supply chain. Recently, several pegmatite-hosted rare metal (Li-Rb-Be-Nb-Ta) deposits have been discovered in the Western Kunlun orogenic belt, making it a new world-class rare metal resource (estimated ~7 Mt Li2O and 0.16 Mt BeO). Understanding the metallogenesis of this belt is critical to further evaluate the rare metal potential. In this study, columbite-tantalite (coltan) and monazite from rare metal pegmatites and zircon from potential parental granites were collected from five representative rare metal pegmatite deposits in the western, middle, and eastern parts of the Western Kunlun orogenic belt for U-Pb geochronology. The results indicate that despite the distances of the sampling localities in different parts of the Western Kunlun orogenic belt, the ages of pegmatite-hosted rare metal mineralization fall in a narrow range of ca. 208–204 Ma. These rare metal pegmatites are temporally and spatially related to adjacent postorogenic granites emplaced following the closure of the Paleo-Tethys Ocean. The compositional characteristics of K-feldspar, biotite, and muscovite of the granites and pegmatites, along with regional mineralogical and textural zonation of the pegmatites, suggest that the rare metal pegmatites were derived from the volumetrically much more important, highly fractionated granitic intrusions. We propose that, in combination with the data from previous studies, the 218–204 Ma interval represents a newly recognized rare metal metallogenic period linked with granitic intrusions in the Western Kunlun orogenic belt, revealing a 600-km-long late Triassic rare metal pegmatite belt composed of multiple ore fields formed in a similar metallogenic setting. These results emphasize the importance of identifying fertile, Late Triassic to Early Jurassic granitic intrusions for rare metal pegmatite exploration. Furthermore, combined with recent studies on the Songpan-Ganzi rare metal pegmatite belt along the eastern segment of the Paleo-Tethys, this study further highlights the great potential of rare metal resources in this global tectonic zone.

Mineralization of the Shangjiazhuang Mo deposit in the Jiaodong peninsula, China: Constraints from S–H–O isotopes and fluid inclusions

The Shangjiazhuang Mo deposit is located in the east of Shandong Peninsula, which is tectonically the eastern extends of the Dabie-Sulu orogenic belt. The ore bodies occur in the Early Cretaceous Yashan porphyritic granodiorite, which are stratiform, vein-like and lentoid. The orebodies are controlled by the fractures with NW direction, and have similar orientations, with strike of 337°–344° and dips of 20°–26° to the northeast. The potassic alteration, biotitization, silicification, sericitization, chloritization, and carbonatization are developed in the country rock. According to the relationship of mineral symbiotic assemblage and the cutting relationship of the hydrothermal veins, the hydrothermal metallogenic period of Shangjiazhuang Mo deposit can be divided into three stages: quartz-molybdenite (early stage), quartz-chalcopyrite and molybdenite (middle stage) and quartz-pyrite (late stage). We studied S–H–O isotopes, fluid inclusions and mineralization age of the Shangjiazhuang Mo deposit, aiming to clarify the genesis mechanism for the Mo deposits in the eastern Jiaodong Peninsula. The δ34S value of molybdenite and chalcopyrite in the main metallogenic stage range from 4.5‰ to 5.0‰, which is consistent with magmatic sulfur. The δ18OH2O valve decrease gradually from the early metallogenic stage (4.5‰–5.0‰) to the late metallogenic stage (0.39‰–1.48‰), indicating that the ore-forming fluids were mainly magmatic water at the early stage and a mixture of meteoric and magmatic water at the late stage. The ore-forming fluids evolved from moderate temperature, CO2-rich and high salinity at the early stage to low temperature, CO2-poor with nearly constant salinity in the late stage. Different types of inclusions with similar temperature and different salinity coexist in the main metallogenic period, indicating that as temperature drops, fluids in the system were either immiscible or boiling, leading to CO2 escape, and finally leads to the precipitation and enrichment of ore-forming elements.

Tectonics, geochronology, and mineralization of the Shuidegou gold deposit in the Mianlue belt, western Qinling Mountains, China

The gold mineralization in the Mianlue belt, western Qinling Mountains, has been a hotspot in geoscience research in recent years. In particular, important breakthroughs have been achieved in terms of prospecting in the medium-sized Shuidegou gold deposit, located in the middle of the Mianlue belt. Here, we present the results of systematic tectonic and chronological analyses conducted on the Shuidegou gold deposit. The reconstructed zircon U–Pb chronologies of the ore-bearing altered rocks and of the ore-bearing vein demonstrated that the Shuidegou gold deposit formed at ~183 Ma and was further enriched at ~ 150 Ma. The macro- and micro-structures identified in deformed geologic bodies and quartz c-axis fabrics in the mining area suggest a division of the deformation sequence into four phases, corresponding to: (1) a Mid–Late Triassic collision and convergence of middle–deep deformation structures during the main orogenic period (D1); (2) a Late Triassic–Early Jurassic collision and convergence during the late-stage thrust-nappe tectonic deformation (D2); (3) a Mid–Late Mesozoic shallow strike-slip shear structure stage during intracontinental orogeny (D3); (4) post-Cretaceous, shallow brittle thrust extrusion strike-slip structure (D4). Based on the deformation and zircon U–Pb chronological features of the Shuidegou gold deposit, we believe that the main metallogenic age (~183 Ma) corresponds to the thrust-shear deformation stage (D2) and that it is genetically connected with magmatism. Notably, the late-stage further enrichment(~150 Ma) occurred in the sinistral strike-slip stage. Ore-bearing fluids may have been restricted by the far-field effect of the Pacific plate subduction along the eastern edge of East Asia. Based on the macro- and micro-deformation features, the chronological data relative to the key geologic bodies, and the regional geologic background, we subdivided the mineralizing process of the Shuidegou gold deposit is composed into three stages: (1) the formation of an ore-guiding channel, (2) the deposition and mineralization of ore-forming elements, and (3) a later further enrichment. The study of ore-controlling structure showed that the development of the Shuidegou gold deposit was mainly controlled by WNW- (E–W) and NNE-trending structures during the two metallogenic periods (~183 Ma and ~ 150 Ma, respectively). Concerning this aspect, the Shuidegou gold deposit contrasts with some typical gold deposits in the same region.

Metallogeny of the Ergu Fe-Zn polymetallic deposit, central Lesser Xing’an Range, NE China: Evidence from skarn mineralogy, fluid inclusions and H-O-S-Pb isotopes

The Lesser Xing'an Range is an important skarn Fe-Zn metallogenic area in Northeast China. To reveal the metallogenic characteristics and attributes of the skarn deposits and establish geological model for deposit formation and prospecting, we selected the Ergu skarn Fe-Zn polymetallic deposit for comprehensive study, including detailed field observation and petrographic, mineralogy, fluid inclusions (FIs), and H-O-S-Pb isotope analyses. The ore bodies can be divided into magnetite, magnetite-sphalerite, pyrrhotite-pyrite-arsenopyrite, copper polymetallic and galena-sphalerite ore bodies. These ore bodies hosted in the contacts between the granodiorite and carbonate rocks of the lower Cambrian Qianshan Formation. The ore-forming processes involved two metallogenic periods–the skarn period (I) and quartz-sulfide period (II), including six stages. The prograde skarn stage (I1) is characterized by garnet and pyroxene. The retrograde skarn stage (I2) is dominated by epidote, actinolite, chlorite, hornblende and a few magnetite. The oxide stage (I3) is typified by abundant magnetite, with lesser amounts of epidote, quartz, molybdenite and pyrrhotite. The quartz-Fe-Cu sulfide stage (II1) is enriched in pyrite, pyrrhotite, arsenopyrite, chalcopyrite and quartz. The quartz-Pb-Zn sulfide stage (II2) is enriched in galena, sphalerite and quartz. The quartz-carbonate stage (II3) is typified by the formation of quartz, calcite and fluorite.Electron probe microanalysis (EPMA) showed that the garnets are composed of reddish-brown to yellowish-green andradite (And63.7~939Gro1.15~34.6Ura + Pyr + Spe1.55~5.00) and brown grossular (And22.4~48.1Gro46.0~74.9Ura + Pyr + Spe1.82~3.22) (Ura-Uvarovite, And-Andradite, Pyr-Pyrope, Spe-Spessartine, Gro-Grossular). The pyroxene is composed of light green diopside (Di81.2~93.7Hd5.30~17.2Jo1.03~1.98) (Di-Diopside, Hd-Hedenbergite, Jo-Johannsenite); the epidote has a high pistacite component (Ps value) (Fe3+/(Fe3++Al) = 0.09–0.18) and Fe3+/Fe2+ value (1.17–4.67). These skarn mineral assemblages record the transition from weakly acidic to alkaline, and an oxidized condition for the skarnization process.The FIs mainly include daughter mineral-bearing three-phase (S-type), liquid-rich (W1-type) and vapor-rich (W2-type) FIs. Laser Raman analysis suggest that the gas phase composition of FIs are dominated by H2O and CO2, and a few CH4. Based on fluid inclusions (FIs) and H-O isotopes studies, the skarn period was formed at high temperature (341–467 °C), low to high salinity (1.22–40.2 wt%) and originated from magmatic-hydrothermal fluids (δ18OH2O = 2.58‰ to 10.2‰, δDH2O = −70.7‰ to −63.8‰). Fe-Cu sulfide-forming stage (stage II1) shows clear meteoric water input, as constrained from the δ18OH2O (8.25‰ to 11.7‰) and δDH2O (−114‰ to −106‰) values. In this stage, the ore-forming fluids belong to a H2O-NaCl-CO2 ± CH4 system with moderate to high temperatures (247–360 °C) and low salinities (1.22–7.15 wt%). This system lasted until stage II2 with moderate-high temperatures (193–306 °C) and low salinities (1.56–4.17 wt%). Finally, in stage II3, the fluid transitioned into a homogeneous H2O-NaCl system with low to moderate temperature (169–263 °C) and low salinity (1.39–4.48 wt%).The sulfur isotope (δ34S = 2.2–4.6%) and lead isotopic (206Pb/204Pb = 18.0–18.6, 207Pb/204Pb = 15.5–15.6, 208Pb/204Pb = 37.8–38.2, similar to granodiorite) compositions of sulfides indicate that the ore-forming materials were mainly derived from granodioritic magma. Based on the above research results, we propose that the Ergu deposit is a typical Fe-Zn skarn deposit and the main mechanisms of mineral precipitation were fluid boiling and cooling.

Extensive mineralization in the eastern segment of the Xingmeng orogenic belt, NE China: A regional view

• There are four types of EXOB deposits: porphyry , skarn , hydrothermal vein, and epithermal types. • There are five stage mineralizations in EXOB: 480–440, 300–220, 200–165, 155–130, and 125–100 Ma. • The five metallogenic periods correspond to different geological setting. The eastern segment of the Xingmeng orogenic belt (EXOB) hosts numerous Mo, polymetallic Ag, Pb–Zn , Sn, Cu, Au (Ag), and rare-earth element (REE) deposits and is one of the most important polymetallic-ore regions globally. The mineralization type includes i) porphyry Cu (Mo, Au), Mo (Cu, Pb–Zn, W), Sn (Cu–Ag) deposits, ii) skarn Cu–Au, polymetallic Pb–Zn and Fe–Sn deposit, and iii) veined polymetallic Ag, Pb–Zn, Sn, Cu deposits and W, Mo deposits, with an REE deposit related to magmatic hydrothermal fluid; and iv) epithermal Ag and Au (Ag, Te) deposits, respectively. The mineralization-related rocks in the EXOB are mainly high-K calc-alkaline granites together with minor alkaline granites that were derived from the melting of juvenile crust. The mineralizations in the EXOB are typically related to magmatic-hydrothermal events. In this study we attempt a systematic analysis of the temporospatial distribution of ore deposits in the EXOB, in order to constrain the geodynamic setting of mineralization. Based on available geochronological data, we suggest five mineralization stages for the EXOB at 480–440, 300–220, 200–165, 155–130, and 125–100 Ma, respectively. The porphyry Cu–Mo mineralization occurred during the early Paleozoic (480–440 Ma). The extensive Mo (W, Sn), and Ag (Pb–Zn) polymetallic mineralization was formed during the Mesozoic. The Ordovician–Triassic mineralization (480–220 Ma) is related to the Paleo-Asian Ocean tectonism and developed in an island arc setting. The Permian–Triassic mineralization (300–220) was formed in a post-collisional tectonic setting related to the development of Hegenshan suture. The early–middle Jurassic deposits (200–165 Ma) are related to the subduction of the Paleo-Pacific oceanic plate on the East Asian continental margin. The Late Jurassic–Early Cretaceous deposits (155–130 Ma) were formed in an extensional setting related to rollback of the Paleo-Pacific Plate. The Jurassic–Cretaceous mineralization (200–100 Ma) in the northern segment of the Da Hinggan Mountains is associated with the subduction and post-collisional tectonic setting of the Mongol–Okhotsk oceanic plate. The latest stage of epithermal deposits (125–100 Ma) were developed in a continental margin back-arc setting associated with subduction of the Paleo-Pacific Plate beneath the Eurasia.

Petrogenesis and metallogenic potential of the early devonian Yugusayi mafic-ultramafic complex in Qimantagh, East Kunlun orogeic belt

ABSTRACT The Yugusayi mafic-ultramafic complex, located in the Qimantagh area, East Kunlun orogenic belt, consists of harzburgite, olivine orthopyroxenite, hornblende pyroxenite, and hornblende gabbro, which were once considered to be a part of the Early Palaeozoic ophiolite suite. However, the Yugusayi mafic-ultramafic rocks are characterized by thermal emplacement, accompanied by Cu-Ni sulphide mineralization, which is different from typical ophiolite suite. The LA-ICP-MS zircon U-Pb dating yields a 405 ± 2.8 Ma age for the hornblende gabbro, which belongs to the Early Devonian. All rocks are enriched in LREE but depleted in HREE, with a characteristic of ferrous mafic-ultramafic rocks. The εHf(t) values of the zircons from hornblende gabbro are 5.6–14.8, the εNd(t) values of whole rocks are from −4.27 to 0.08, and the δ34S values of sulphide are 1.36–8.72‰, indicating that the magma originated from the depleted mantle and contaminated by continental crust material during the ascending process. Based on the regional geological background, it is reasonable that the rocks formed in the post-collision extension stage after the closure of the Proto-Tethys Ocean and the continental collision, which represents an important metallogenic period for Cu-Ni sulphide deposits in the East Kunlun oregenic belt. Early Devonian magmatic mafic-ultramafic intrusions are developed in the early Palaeozoic ophiolitic tectonic melange belt of Qimantagh area. Combined with good metallogenic conditions and remarkable mineralization characteristics, it is believed that the Qimantagh area is a potential area for the prospecting of magmatic Cu-Ni sulphide deposits.

The La Bellière gold and antimony district (French Armorican Massif): A two-stage evolution model controlled by Variscan strike-slip tectonic

The La Bellière gold district, in the Ligerian domain of the Armorican Massif is the third one of France in term of production. It shows gold-bearing quartz veins neighboring with a complex network of Sb veins, hosted in the Neoproterozoic metasedimentary basement of the Mauges Nappe. New structural data, mineralogical, textural and geochemical assays have been carried out to clarify the gold and Sb veins relationships. Our results favor of two-step hydrothermal event with an early deep-seated gold event followed by a late shallower Sb event. The gold-bearing quartz veins are hosted by N60°E to N90°E sinistral strike-slip faults. These veins exhibit a four-stage paragenesis: 1) early barren quartz filling, 2) arsenopyrite-pyrite with minor scheelite assemblage, 3) gold and base metal sulfides crystallized after a ductile/brittle deformation stage, and 4) pyrite-carbonate coeval with a late brittle stage. These results support a continuous evolution model from a deep emplacement level (12 to 9 km) to a shallow one (7 to <5 km) with a brutal change in the P/T conditions that triggered the deposition of gold (stage 2) controlled by a seismic-valve mechanism. On the contrary, Sb veins correspond to open space vein types, hosted in a N20°W to N20°E conjugated strike-slip fault network arranged in a Riedel shear model, controlled by N130-140°E regional dextral strike-slip shear zone associated to the South Armorican Shear Zone system. A two-stage evolution is recognized, the first one consists of early pyrite-arsenopyrite with microcrystalline quartz, followed by a late stibnite stage formed after geodic quartz deposition. Quartz texture argues for a shallow emplacement (<5 km) of veins controlled by a suction-pump mechanism. Chronologically, the gold vein opening complies with a NE-SW maximum shortening direction different from the late-Variscan stress field responsible for the dextral Armorican shear zone during late Carboniferous, and constrains an indirect dating. Thus, a Visean age is proposed for the formation of gold veins. The overall features of gold deposits are close to those of mesozonal orogenic gold deposits in Europe. Conversely, Sb-bearing veins are generated by a N-S shortening during the late Carboniferous. The Sb event, distinct in time from the earlier gold one, might correspond to a different expression of the so-called “epizonal” type in the orogenic gold model. It is proposed that the Late Carboniferous “Or 300” event is not the unique metallogenic period for gold deposition in the French Variscan domain. Our study highlights the role of the sinistral strike-slip shearing of possible Visean age, in the gold metallogenesis of the Ligerian domain.

Discrete Jurassic and Cretaceous Mineralization Events at the Xiangdong W(-Sn) Deposit, Nanling Range, South China

Abstract The Xiangdong W(-Sn) deposit is hosted in the Dengfuxian multiphase granites (biotite, two-mica, and muscovite granites) within the Nanling Range metallogenic belt in south China. Previous studies suggested that the W(-Sn) mineralization in the Xiangdong deposit is related to the Late Jurassic two-mica granite, whereas recently W-Sn–bearing quartz veins have also been identified in muscovite granite. We present new cassiterite and zircon U-Pb ages to constrain the timing of W-Sn mineralization and related granitic magmatism. Our laser ablation-inductively coupled plasma-mass spectrometry U-Pb dating of zircon grains, combined with previous zircon ages, in addition to the trace element composition of the muscovite granite, suggest the muscovite granite in the Dengfuxian pluton was emplaced at 145 to 142 Ma and shows highly evolved features. Cassiterite grains from the ore-bearing veins in two-mica granite yielded U-Pb ages of 151.6 ± 3.7 and 141 to 138 Ma, whereas cassiterite grains from quartz veins occurring in muscovite granite yielded a U-Pb age of 136.8 ± 3.3 Ma. The new ages and detailed geologic evidence indicate that the Early Cretaceous muscovite granite is also genetically related to W-Sn mineralization. Combining this with previously published data from the Late Jurassic two-mica granites and related mineralization, we suggest that there were two stages of W-Sn mineralization at Xiangdong. Arsenopyrite geothermometry from the two stages suggests temperatures of 300° to 491° and 308° to 450°C in stage I and stage II, respectively. Wolframite grains from the two stages also show different characteristics and patterns for their major and trace elements. The enrichment in Sc in wolframite suggests low-pH and low-Eh conditions for a fluid containing F– and/or PO43− complexes during stage I, whereas higher contents of Nb and Ta and lower contents of Sc in wolframite from stage II indicate relatively lower pH and higher Eh conditions. In combination with data from other recent studies, we propose that the 145 to 130 Ma interval represents a newly recognized W-Sn metallogenic period linked with highly evolved granites in the Nanling Range metallogenic belt. The Early Cretaceous muscovite granite is an important new target for W and Sn resources in south China.

Formation of the Liaoshang gold deposit, Jiaodong Peninsula, eastern China: Evidence from geochronology and geochemistry

The Liaoshang gold deposit in the Jiaodong area of the Shandong Province is best known for its super‐large size. Situated on the north‐eastern margin of the Jiaolai Basin, it forms a part of the Jiaobei terrane of the North China Block. Approximately 20 ore bodies within the Liaoshang gold deposit have been explored; of these, four are structurally controlled gold‐bearing pyrite–dolomite vein‐type deposits. These ore bodies lie in an NE‐trending altered fracture zone and are characterized by their thickness and high‐grade ores. The wall rocks of the ore bodies consist of Paleoproterozoic Jingshan Group metamorphic rocks and Mesozoic granites. Gold is hosted mainly in pyrite and dolomite. The ore is divided into two subtypes—the dominant pyrite–dolomite vein subtype and the subordinate altered rock subtype which contains pyrite and dolomite. Fluid inclusions within dolomite indicate that the main metallogenic period was dominated by a CO2–NaCl–H2O fluid system that had low‐moderate salinity, low density, high abundance of CO2, and a small amount of N2. The ore formed at 81‐ to 94‐MPa pressure and between 2.97‐ and 3.24‐km depth. Research on the S, Pb, C, O, and He–Ar isotopes in the gold‐bearing minerals suggests that the ore‐forming material was mainly crustal in origin, with some degree of crust–mantle mixing. The application of Rb–Sr isotope analysis to gold‐bearing pyrite yields a metallogenic age of 105.5 ± 9 Ma. The Sm–Nd isotope analysis of dolomite yields an age of 104.8 ± 5.1 Ma. We propose that gold mineralization in the Jiaodong area occurred in two phases: the early Early Cretaceous for gold deposits in the north‐west and the late Early Cretaceous for gold deposits in the east.

Discussion on the Minerogentic Series of Gold Deposit in Qinghai

Gold is one of the most important strategic minerals in Qinghai province. Based on the metallogenic characteristics, types, ore control factors and spatial distribution of gold deposits, the metallogenic regularities of gold deposits were put forward. It’s divided the pre-Cambrian, Early Paleozoic, Late Paleozoic, Mesozoic and Cenozoic the metallogenic series assemblages, and also their distribution features are discussed which focus on five metallogenic periods. According to the theory of metallogenic series of ore deposits, combining with characteristics of typical gold deposits, twenty metallogenic series are preliminarily divided in Qinghai province. It is pointed out some suggestions about prospecting and exploration of gold deposits in Qinghai.