Jing-Gui Sun

Early Cretaceous arc magmatism and high-sulphidation epithermal porphyry Cu–Au mineralization in Yanbian area, Northeast China: the Duhuangling example

Yanbian area (Northeast China) is part of the Western Pacific porphyry–epithermal gold–copper metallogenic belt. Here, we present the results of a detailed study of Early Cretaceous mineralization-associated magmatic events in this region and, based on the results, identify the geological setting and mineralizing processes involved in mineral deposit formation. We focus on the timing and geodynamic mechanisms of hydrothermal alteration and metallogenesis of the Duhuangling high-sulphidation epithermal gold deposit, located ~15 km NW of the large Xiaoxinancha gold-rich porphyry copper deposit. New data are presented for zircon U–Pb, fluid inclusion Ar–Ar, whole-rock geochemical, and in situ zircon Hf isotopes for igneous rocks of the Duhuangling deposit, and the data – integrated with results of previous research – reveal that Yanbian area epithermal and porphyry Cu–Au deposits are associated with two stages of Early Cretaceous intermediate-felsic magmatism (116–118 and 112–109 Ma), with the later stage of magmatism more closely associated with mineral deposit formation. Our new data constrain the timing of formation of high-sulphidation epithermal gold deposits to 108–106 Ma and the timing of formation of gold-rich porphyry copper deposits to 111–109 Ma. The two stages of magmatism are associated with magmas derived from different sources, with the first-stage magmas potentially derived from partial melting of a depleted mantle wedge that had been metasomatized by subducted slab-derived fluids or melts; these first magmas are also mixed with material derived from the underplated lower crust. Second-stage magmas were probably generated by partial melting of subducting oceanic slab and some oceanic sediments and the interaction of these magmas with melts derived from the overlying lower crust. Most mineralization in the study area is associated with Cu- and Au-rich post-magmatic hydrothermal fluids that were generated during fractionation of hydrous, sulphur-rich, and high oxygen fugacity adakite-like/adakitic mixed magmas. The formation of both igneous rocks and mineral deposits in the study area occurred in a tectonic setting dominated by Late–Early Cretaceous subduction of the Izanagi or Pacific Plate beneath eastern Asia, indicating that the formation of epithermal and porphyry Cu–Au deposits in the Yanbian area involved subduction-derived fluids, melt modification, partial melting, magma mixing, and crystal fractionation.

Oldest zircon xenocryst (4.17 Ga) from the North China Craton

Prior to this work, the existence of crustal materials older than 4.0 Ga has not been reported from the North China Craton (NCC) – one of the few global terrains where crustal rocks from ∼3.8 Ga have been identified. Here we report the first occurrence of a xenocrystic zircon with a 207Pb/206Pb age of 4174 ± 48 Ma, from the Anshan–Benxi Archaean supracrustal greenstone belt, based on laser ablation–inductively coupled plasma–mass spectrometry. The 4.17 Ga zircon xenocryst is hosted within ∼2523 ± 12 Ma massive fine-grained amphibolites which were subsequently metamorphosed at ∼2481 ± 19 Ma. The xenocryst age is ca. 350 million years, older than the oldest zircon previously identified in the NCC, and is consistent with prior zircon Lu–Hf isotopic studies. Documentation of 4.17 Ga xenocrystal zircon not only provided a geochronological record of the oldest known crustal materials in the NCC, but also identified the geologic environment for further search for the rocks that formed during Earth’s earliest recorded evolution.

Geology and ages of porphyry and medium- to high-sulphidation epithermal gold deposits of the continental margin of Northeast China

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.

Zircon U–Pb–Hf isotopes and bulk-rock geochemistry of gneissic granites in the northern Jiamusi Massif, Central Asian Orogenic Belt: implications for Middle Permian collisional orogeny and Mesoproterozoic crustal evolution

We conducted bulk-rock geochemical and zircon U–Pb–Hf isotope analyses of gneissic granites from the northern Jiamusi Massif, in order to investigate their sources, petrogenesis, and geodynamic significance. Zircons contain fine-scale oscillatory zoning with high Th/U ratios (0.12–0.80), indicative of a magmatic origin. U–Pb dating indicates that they formed during the middle Permian (264 ± 4.2 Ma to 268.6 ± 0.81 Ma), and contain a 531 Ma inherited zircon core. The gneissic granites have high contents of K2O + Na2O and Al2O3, and low MgO and CaO. With A/CNK ratios of 1.01–1.11, they are classified as peraluminous calc-alkaline to alkaline S-type syn-collisional granites. Enriched in large ion lithophile elements such as K, Rb, Ba, and Th, they are depleted in high field strength elements such as Nb, Ta, and Ti. Bulk-rock geochemical analyses display moderately negative Eu anomalies (Eu/Eu*) of 0.36–0.52, and (La/Yb)N ratios of 13.24–29.51. In situ Hf analyses of zircon gave ϵHf(t) values of –0.1 to –3.2 and crustal average model ages ( ) of 1.35–1.4 Ga. These data suggest that the gneissic granites formed by partial melting of Mesoproterozoic continental crust during a middle Permian collisional event. Hf isotopes indicate the substantial presence of Mesoproterozoic juvenile crust in the northern Jiamusi Massif, derived from depleted mantle that underwent crustal contamination at 1.4–1.35 Ga. The Jiamusi Massif provides a local record of the assimilation and subsequent rifting of the Rodinia–Gondwana supercontinent.

Early Cretaceous gold mineralization in the Lesser Xing’an Range of NE China: the Yongxin example

ABSTRACT The northern Lesser Xing’an Range in NE China hosts many gold deposits. However, genesis and tectonic background for the mineralization remain unclear. The newly discovered Yongxin gold deposit in this region provides a good example for understanding the related issues. Two economic orebodies have been recognized at Yongxin and they are mainly hosted in the hydrothermal breccias. Zircon U–Pb ages of granite porphyry and diorite porphyry are 119.3 ± 0.7 Ma and 119.9 ± 0.6 Ma, respectively. These data provide constraints to the upper limit of ore-forming age. The δ34S values of pyrite from orebodies range from 2.3‰ to 5.1‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the pyrite are of 18.126–18.255, 15.492–15.537 and 37.880–38.019, respectively. The δ18OH2O and δD values of ore-forming fluids range from −12.5‰ to 1.8‰ and from −124.8‰ to −102.1‰, respectively. The REE compositions of gold-bearing pyrite are similar to those of the volcanic rocks of the Longjiang formation, diorite porphyry and granite porphyry. The combined geological, geochronological and geochemical characteristics of the Yongxin gold deposit indicate that the ore-forming materials were likely sourced from the volcanic rocks of the Longjiang formation, diorite porphyry and granite porphyry, whereas the ore-forming fluids are dominated by meteoric water. The Yongxin gold deposit could be a product of the Early Cretaceous large-scale gold mineralization in northeast China which occurred in an extensional tectonic setting and were related to the rollback of the subducted Paleo-Pacific Oceanic Plate beneath the continental margin of northeast China.