The Huangshandong deposit, located in the Central Asian Orogenic Belt (CAOB), is the largest Ni–Cu sulfide deposit in the eastern Tianshan and Beishan regions of China. The deposit is hosted in a postorogenic intrusion that comprises diorite, gabbrodiorite, bojite, olivine gabbro, gabbronorite, troctolite, and lherzolite. Here, we report the Permian zircon U–Pb crystallization ages of 278.5 ± 2.1 Ma, 278.1 ± 1.9 Ma, and 279.6 ± 1.9 Ma for the olivine gabbro, bojite, and gabbrodiorite, respectively, as well as geological, petrological, and geochemical data for the various lithofacies of the deposit. As a result of the edge cooling effect, the intrusion cooled rapidly from the outside inwards as follows: crystallizing diorite → gabbrodiorite → gabbro → lherzolite → gabbronorite. In addition, further tectonic activity resulted in the injection of a more primitive magma in place, which crystallized the lherzolite in the bottom and middle transitional zones of the intrusion. The crystallization sequence of the intrusion is generally as follows: olivine → orthopyroxene + labradorite → clinopyroxene + labradorite → amphibole + andesine. At the beginning of mineral crystallization, the metalliferous magma was segregated due to sulfide immiscibility and separated by gravity. With gabbronorite crystallization, the immiscible liquid sank to the base of the magma chamber and crystallized as Cu‐ and Ni‐rich sulfides. Tholeiitic and calc‐alkaline rocks are characterized by relative enrichment in large‐ion lithophile elements and depletion in high‐field‐strength elements, and values of Th/Ta (2.25–5.94), (Nb/La) N (1.88–4.39), and Th/Nb (0.29–0.82) indicate that the mantle source was composed of a dehydrated subducted plate or mantle wedge. In addition, values of Nb/U (2.64–10.68) and Ce/Pb (1.33–3.53) suggest that the magma was contaminated by the continental crust during its ascent along pre‐existing structures in the Carboniferous strata.
The Laozuoshan gold deposit, located in the central part of the Jiamusi Massif, is hosted by the contact zone between granitic complex and Proterzoic strata. In this study, we present the results of geochronology and geochemistry of ore-related granodiorite and diorite porphyry, and hydrothermal sericite 40 Ar/ 39 Ar dating. The granodiorite and diorite porphyry in the Laozuoshan gold deposit are calc-alkaline and high-K (calc-alkaline) series, which are enriched in LREE and LILE and depleted in HFSE, with no depletion of Eu. The geochronology data show that zircon U–Pb ages of the granodiorite and diorite porphyry are ∼262 Ma and ∼105 Ma, respectively. The sericite 40 Ar/ 39 Ar ages are ∼194 Ma and ∼108 Ma. On the basis of previous researches, ore geology and geochronology studies show that the Laozuoshan gold deposit underwent at least two gold mineralization events. We suggest that the first one, which was related to skarnization, resulted from the collision between the Jiamusi and Songnen Massifs in Late Permian. The subsequent gold mineralization resulted from the subduction of the paleo-Pacific Plate in Early Cretaceous.
The Jiapigou mining district (JMD) in the northeastern margin of the North China Craton mainly contains quartz vein- and altered rock-type gold deposits that have been prospected and mined for over 200 years. However, the ore-formation mechanism and geodynamic setting are still limited understood. Here we present new geological, mineralogical, gochronological, geochemical and Hf isotopic evidences of the ore-related intrusions from the deposits in the JMD to reveal the tectonic setting and genetic relationship between the Au mineralizitions and synchronic magmatism. The results show the following: (1) zircon U–Pb dating of the ore-related intrusions, such as basic dikes (gabbro and porphyritic gabbro), granites, and acid dikes (granite aplite dike and rhyolite porphyry) bracket their emplacement in the range of 177–171 Ma; (2) The basic dikes are characterized by enrichment in large ion lithophile elements (LILEs; i.e., Rb, Ba, and U), moderately depletion of high field strength elements (HFSEs; i.e., Nb and Ta), and high εHf (t) values (–13 to +12.8), whereas granites are characterized by high SiO2 (73.24–75.12 wt%) and total alkali (K2O + Na2O = 5.74–8.58 wt%) concentrations, low TFe2O3 (0.78–1.43 wt%) and CaO (0.98–1.36 wt%) concentrations, enrichment of LILEs (i.e., Rb, Ba, Th, and K) and depletion of HFSEs (i.e., Nb, Ta, Ti, and P), and low high εHf (t) values (–13.6 to –11.0), which features as well as those of the acid dikes. These results indicate that the ore-related intrusions, such as basic dikes, granites, and acid dikes were emplaced during the Middle Jurassic (177–171 Ma), constrained that the giant Au mineraliziton in the JMD occurred in the Middle Jurassic. And the basic dikes were likely derived from an enriched lithospheric mantle source that has been influenced by fluids expelled from a subducted slab, whereas granites and acid dikes were likely derived from partial melting of Archean crustal materials. Combined with regional geological observations, we conclude that the giant Au mineralization and ore-related magmatism occurred in an extensional setting associated with the subduction of the Paleo-Pacific Plate. The basic dikes and granites can be regarded as a precursor for the Au mineraliziton in the JMD. And mantle- and crustal-fluids and metals substantially contributed to the formation of the giant Au mineralization in the JMD.
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 Hongshan complex, located in the southern part of the Taihang Mountains in the central part of the North China Craton, consists of syenite stocks (including fine-grained biotite aegirine syenite, medium-grained aegirine gabbro syenite, coarse-grained aegirine gabbro syenite, syenite pegmatite, and biotite syenite porphyry), with monzo-diorite and monzo-gabbro dikes. This paper presents zircon U-Pb ages and Hf isotope data and whole-rock geochemical data from the Hongshan complex. LA–ICP-MS zircon U–Pb age from the fine-grained biotite aegirine syenite, monzo-diorite, and monzo-gabbro are 129.3 ± 2.0 Ma, 124.8 ± 1.3 Ma, and 124.1 ± 0.9 Ma, respectively, indicating their emplacement in the Early Cretaceous when the North China Craton was extensively reactivated. The monzo-diorite and monzo-gabbro have low SiO2 contents (48.94–57.75 wt%), total alkali contents (5.2–9.4 wt%), and εHf (t) values of −22.3 to −18.4 and are enriched in MgO (4.0–8.2 wt%), Al2O3 (14.3–15.8 wt%), light rare earth elements (LREEs) and large ion lithophile elements (LILEs). Interpretation of elemental and isotopic data suggests that the magma of monzo-diorite and monzo-gabbro were derived from partial melting of the enriched lithospheric mantle metasomatized by slab-derived hydrous fluids. Syenites with high alkali (K2O + Na2O = 9.4–13.0 wt%) and Sr contents (356–1737 ppm) and low Yb contents (0.94–2.65 ppm) are enriched in Al (Al2O3 = 16.4–19.1 wt%), but depleted in MgO (0.09–2.56 w%), Cr (Avg = 7.16 ppm), Co (Avg = 6.85 ppm) and Ni (Avg = 9.79 ppm), showing the geochemical features of adakitic rocks associated with thickened lower crust. Combining zircon 176Hf/177Hf ratios of 0.282176 to 0.282359, εHf(t) values of −18.3 to −11.8 and εNd (t) values of −11.1 to −8.2, we conclude that the syenite magma was derived from the mixing of the thickened lower crust and the enriched lithospheric mantle magma. These magma processes were controlled by Paleo-Pacific plate subduction and resulted in the destruction and thinning of the central North China Craton.
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