The Jiapigou gold ore belt is located in the northeastern corner of the wedge-shaped North China Craton and is hosted by Neoarchean basement gneiss and amphibolite, along with late Palaeozoic and Mesozoic granitoids. In this paper, whole-rock major and trace element geochemistry together with zircon U-Pb ages and Lu-Hf isotope compositions are reported for Late Permian to Triassic igneous rocks from the gold belt. The dominant population of zircons in all these rocks shows oscillatory growth zoning in CL images, and relatively high Th/U ratios (0.10-5.23) that are indicative of a magmatic origin. Zircon U-Pb data indicate that the igneous rocks formed during two major phases: ca. 252 Ma and ca. 230-213 Ma. Geochemically, the Late Permian (ca. 252 Ma) diorites are high-K calc-alkaline in composition and low total Fe 2 O 3 , MgO, and CaO contents, and represented by enrichment in LILEs relative to HFSEs and HREEs, all of which are indicative of a postcollision high-K calc-alkaline granite affinity. In contrast, the Late Triassic (ca. 230-213 Ma) igneous rocks are mainly quartz syenite porphyries, felsites, and granodiorites, and are variable medium-to high-K calc-alkaline series and exhibit a negative Eu anomaly with A-type affinities,indicating an extensional environment. In addition, in situ Hf isotopic analyses of zircons from four dated samples reveal that they have ε Hf (t) values of −3.0 to +2.2, with two-stage model (T DM2 ) ages range from 964 to 1,210 Ma, indicating that they probably originated from the partial melting of a dominantly Mesoproterozoic to Neoproterozoic crustal source. On the basis of the geochemical data and regional geological investigations, we further propose that the Jiapigou gold ore belt in the Late Permian was formed in a postcollisional tectonic setting, whereas an extensional tectonic setting in the Late Triassic that caused lithospheric thinning during a postorogenic event.
The Dongfengshan gold deposit in Heilongjiang Province of China is located at the western margin of the Jiamusi Massif. The mineralization is closely related to the intrusion of the Permian granite porphyry. In this paper, we present new zircon U–Pb ages and whole‐rock geochemical analyses of the granitoids from the Dongfengshan deposit. They are classified as peraluminous high‐K calc‐alkaline to shoshonitic A‐type granites, with enrichment in the large ion lithophile elements (e.g., Rb, U, and Th) and depletion in the high field strength elements (e.g., Nb, P, Ti, and Zr) and clear negative Eu anomalies. The zircons from the granite porphyry are both magmatic and hydrothermal, with the former yielding ages of 281.7 ± 3.3 and 282.1 ± 3.5 Ma that represent the timing of crystallization of this Early Permian pluton. The hydrothermal zircons yield an age of 280.5 ± 0.3 Ma, representing the hydrothermal age, which coincide with the emplacement of the igneous rocks. These data suggest that the Early Permian magmatic and mineralization event led to the formation of the Dongfengshan gold deposit. In comparison, zircons from the monzogranite yield a weighted age of 523.0 ± 6.4 Ma, indicating that magmatism of the study area occurred in the Early Cambrian. On the basis of the regional geological history and the new geochemical and isotopic data from intrusions, we suggest that diagenesis and mineralization of the Dongfengshan gold deposit took place in a postcollisional extensional tectonic setting during the Early Permian.
The Chang’anpu Molybdenum deposit occurs in the monzogranite intrusions in the Lesser Khingan Mountains-Zhangguangcai Mountains metallogenic belt. Previous work focused on the study of deposits, including geological characteristics, mineralization time, S-Pb isotope, etc. However, systematic petrogeochemical study of monzogranite intrusion and comparative analysis with other porphyry deposits in the region are lacking. Three monzogranite dating samples yield LA-ICP-MS zircon weighted mean 206Pb/238U ages of 174.7 ± 1.3 Ma, 174.9 ± 1.4 Ma, and 174.3 ± 1.8 Ma, respectively, indicating that the magmatism occurred in the middle Jurassic of Mesozoic. The 14 monzogranite samples show alkali rich and relatively high silica content (up to 84.39%) with the differentiation index (DI) ranges from 86 to 96, showing that monzogranite have been subjected to fractional crystallization during its evolution; the depletion of Ba, Sr, P, Nb, Ti, and Eu also indicates that the rock has undergone crystallization fractionation, the monzogranite belong to the highly fractionated I-type. Positive εHf(t) values (6.72–8.85) and young TDM2 (551–673 Ma) of the monzogranite indicate that the formation of Chang’anpu monzogranite intrusion is related to the partial melting of juvenile lower crust, originated from the Mesoproterozoic depleted mantle. The magmatism and related Mo mineralization in the Chang’anpu deposit occurred in an active continental margin setting associated with westward subduction of the Paleo-Pacific plate beneath the Eurasian plate.
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