Abstract The margin of NE China, a part of the West Pacific metallogenic belt, contains innumerable low-sulphidation mineral deposits. Gold deposits in this region can be classified into three distinct types based on geology and ore mineral paragenesis: (1) low-sulphidation epithermal silver–gold deposits, (2) low-sulphidation tellurium–gold deposits, and (3) low-sulphidation epithermal tellurium–gold deposits. Ores formed during the late Early Cretaceous and the early Late Cretaceous reflect three distinct metallogenic periods: the Fuxin Stage at 115.98 ± 0.89 Ma, the Quantou Stage at 107.2 ± 0.6 Ma or <103 Ma, and the Qingshankou or Yaojiajie Stage at < 97 Ma and 88.2 ± 1.4 Ma. The Fuxin Stage is dominated by trachyandesitic magmatism, with magmas emplaced at hypabyssal depths. In comparison, the Quantou Stage is characterized by high-K calc-alkaline, calc-alkaline, and sodic andesitic, dacitic, and rhyolitic magmatism of three different suites. The first of these is a high-K calc-alkaline andesitic magmatic suite that was accompanied by the emplacement of a calc-alkaline sodic dacite during the formation of the Ciweigou and Wufeng ore deposits. The second suite is dominated by calc-alkaline sodic rhyolite and high-K calc-alkaline sodic dacite magmatism associated with the formation of the Sipingshan ore deposit. The third suite is typified by high-K calc-alkaline andesitic magmatism associated with the emplacement of calc-alkaline hypabyssal granitoid complexes accompanying the formation of the Dong'an and Tuanjiegou ore deposits. The Qingshankou or Yaojia Stage is characterized by calc-alkaline sodic dacite magmatism associated with the formation of the Wuxing ore deposit. Metallogenesis during the Fuxin Stage characterized by trachytic magmatism is closely related to the formation of a deep-seated fault within a magmatic arc or the back-arc region of an immature continental margin and is associated with the Early Cretaceous subduction of the Pacific plate beneath Eurasia. Ore deposits that formed during the Fuxin Stage were generally related to magmato-hydrothermal fluids associated with mantle-derived magmas. In contrast, metallogenesis during the Quantou and Qingshankou or Yaojiajie stages was closely related to the formation of a mature high-K calc-alkaline magmatic arc within a continental margin setting again associated with the westward subduction of the Pacific plate. This metallogenic event was a product of magmato-hydrothermal systems derived from crust–mantle interaction and mixing of magmas derived from partial melting of different sections of the continental crust. Keywords: mineral deposit typeslow-sulphidation epithermal gold depositore-forming processescontinental margin of NE ChinaWest Pacific metallogenic belt Acknowledgements This research work was jointly supported by the National Natural Science Foundation of China (grant nos. 40772052 and 41172072), Project for Scientific and Technology Development (grant no. 20100450), Chinese Geological Survey Programme (grant no. [2010]26-06), and Geological Survey of Heilongjiang Province (grant no. 3R1101604422). We sincerely thank the staff of the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, for analyses of U–Pb dating of zircon.
Abstract The Laowangzhai gold deposit, located in the Ailaoshan gold belt (SW China), is hosted in various types of rocks, including in quartz porphyry, carbonaceous slate, meta‐sandstone, lamprophyre, and altered ultramafic rocks. In contrast to other wall rocks, the orebodies in altered ultramafic rocks are characterized by the occurrence of a large amount of Ni‐bearing minerals. The ore‐forming process of the orebodies hosted by altered ultramafic rocks can be divided into two stages: pyrite‐vaesite‐native gold and gersdorffite‐violarite stages. The contents of As and Sb increased during the evolution of ore‐forming fluid based on the mineral assemblages. Thermodynamic modeling of the Ni‐Cu‐As‐Fe‐S system using the SUPCRT92 software package with the updated database of slop16.dat indicates the f S 2 in ore‐forming fluid decreases significantly from stage I to stage II. The decreases of f S 2 due to crystallization of sulfides and f O 2 due to fluid–rock reaction were responsible for ore formation in altered ultramafic rocks of the Laowangzhai gold deposit. Geological evidence, the in situ sulfur isotope values of pyrite, and the other published isotopic data suggest that the ore‐forming fluid for ultramafic rock ores was dominantly composed of evolved magmatic fluid with the important input of sediments.
The Dayingezhuang gold deposit, hosted mainly by Late Jurassic granitoids on Jiaodong Peninsula in eastern China, contains an estimated 170 t of gold and is one of the largest deposits within the Zhaoping fracture zone. The orebodies consist of auriferous altered pyrite–sericite–quartz granites that show Jiaojia‐type (i.e., disseminated and veinlet) mineralization. Mineralization and alteration are structurally controlled by the NE‐ to NNE‐striking Linglong detachment fault. The mineralization can be divided into four stages: (K‐feldspar)–pyrite–sericite–quartz, quartz–gold–pyrite, quartz–gold–polymetallic sulfide, and quartz–carbonate, with the majority of the gold being produced in the second and third stages. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein minerals: NaCl–H 2 O (A‐type), CO 2 –H 2 O–NaCl (AC‐type), and pure CO 2 (PC‐type). Quartz crystals in veinlets that formed during the first stage contain mainly AC‐type fluid inclusions, with rare PC‐type inclusions. These fluid inclusions homogenize at temperatures of 251°C–403°C and have low salinities of 2.2–9.4 wt% NaCl equivalent. Quartz crystals that formed in the second and third stages contain all three types of fluid inclusions, with total homogenization temperatures of 216°C–339°C and salinities of 1.8–13.8 wt% NaCl equivalent for the second stage and homogenization temperatures of 195°C–321°C and salinities of 1.4–13.3 wt% NaCl equivalent for the third stage. In contrast, quartz crystals that formed in the fourth stage contains mainly A‐type fluid inclusions, with minor occurrences of AC‐type inclusions; these inclusions have homogenization temperatures of 106°C–287°C and salinities of 0.5–7.7 wt% NaCl equivalent. Gold in the ore‐forming fluids may have changed from Au(HS) 0 as the dominant species under acidic conditions and at relatively high temperatures and f O 2 in the early stages, to Au(HS) 2– under neutral‐pH conditions at lower temperatures and f O 2 in the later stages. The precipitation of gold and other metals is inferred to be caused by a combination of fluid immiscibility and water–rock interaction.
The Nancha gold deposit, located in the central part of southern Jilin Province in the northeastern portion of the North China Craton, contains orebodies hosted in a Proterozoic metamorphosed volcanic–sedimentary sequence. The distribution of the orebodies is controlled by NNE-trending brittle–ductile shear zones and faults. The gold orebodies consist of auriferous quartz veins and auriferous altered rocks. Mineralization can be divided into three stages: (1) quartz–pyrite, (2) quartz–gold–polymetallic sulfide, and (3) quartz–carbonate, with gold being introduced mainly in the second stage. Three types of fluid inclusions were identified in the vein mineral assemblages based on petrography and laser Raman spectroscopy: NaCl–H2O (W-type), CO2–H2O (C-type), and pure CO2 (PC-type). Crystals in the early quartz–pyrite stage veins mainly contain C-type primary fluid inclusions and rare PC-type inclusions. The fluid inclusions in these veins completely homogenize at temperatures of 273–432 °C and show low salinities of 0.63–7.78 wt.% NaCl equiv. In the middle quartz–gold–polymetallic sulfide stage, all three types of fluid inclusions were observed. These fluid inclusions homogenize at temperatures of 132 to 255 °C and show salinities of 0.83–11.72 wt.% NaCl equiv. In contrast, crystals in the late quartz–carbonate stage contain only W-type fluid inclusions that show homogenization temperatures of 132–255 °C and salinities of 0.35–7.86 wt.% NaCl equiv. These data indicate that the metallogenic system evolved from a CO2-rich metamorphogenic fluid to a CO2-poor fluid due to inputs of meteoric waters. Fluid boiling and mixing caused the rapid precipitation of sulfides and gold. Trapping pressures estimated from boiling C-type fluid inclusions were 152–367 MPa in the ore-forming stage. This suggests an alternating lithostatic–hydrostatic fluid system controlled by a fault-valve activity at a depth of 13.8–15.2 km. One hydrothermal sericite sample from an auriferous quartz vein yielded an 40Ar/39Ar isotopic plateau age of 170.1 ± 1.9 Ma, indicating that mineralization occurred in the Middle Jurassic and was unrelated to the volcanics and intrusions in the mineralized area. The characteristics of H–O–S–Pb isotopes and fluid inclusions suggest that the ore-forming fluids were of metamorphic origin, with the S originating from Proterozoic crustal components and the Pb originating from a mixture of ore-forming metamorphogenic fluids and host rocks. The results, combined with existing data on the regional geology, ore geology, fluid inclusions, H–O–S–Pb isotope geochemistry, age of mineralization, and tectonic setting, indicate that the Nancha gold deposit was an orogenic-type system that formed in a Middle Jurassic accretionary orogenic regime, following subduction of the Paleo-Pacific Plate beneath the Eurasian continent.
The continental margin of Northeast China, an important part of the continental margin-related West Pacific metallogenic belt, hosts numerous types of gold-dominated mineral deposits. Based on ore deposit geology and isotopic dating, we have classified hydrothermal gold–copper ore deposits in this region into four distinct types: (1) gold-rich porphyry copper deposits, (2) gold-rich porphyry-like copper deposits, (3) medium-sulphidation epithermal copper–gold deposits, and (4) high-sulphidation epithermal gold deposits. These ore deposits formed during four distinct metallogenic stages or periods, at 123.6 ± 2.5 Ma, 110–104 Ma, 104–102 Ma, and 95.0 ± 2 Ma, corresponding to periods of Cretaceous intermediate–acid volcanism and late-stage emplacement of hypabyssal magmas along the northern margin of the North China platform. The earliest stage of mineralization (123.6 ± 2.5 Ma) corresponds to the formation of medium-sulphidation epithermal copper – gold deposits and was associated with a continental margin magmatic arc system linked to subduction of the Pacific Plate beneath the Eurasia. This metallogenesis is closely related to high-K calc-alkaline intermediate–acid granite and pyroxene – diorite porphyry magmatism. The second and third stages of mineralization in the study area (110–104 Ma and 104–102 Ma, respectively) correspond to the formation of gold-rich porphyry copper, porphyry-like copper, and high-sulphidation gold deposits, with metallogenesis closely related to sodic or adakitic magmatism. These magmas formed in a continental margin magmatic arc system related to oblique subduction of the Pacific Plate beneath the Eurasia, as well as mixing of crust-derived remelted granitic and mantle-derived adakitic magmas. During the final stage of mineralization (95.0 ± 2 Ma), metallogenesis was closely related to sodic or adakitic magmatism, with diagenesis and metallogenesis related to the disintegration or destruction of the Pacific Plate, which was subducted beneath the Eurasian Plate during the Mesozoic.
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