Shuwen Xing

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.

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.

Characteristics of Disseminated Diaspore in the Longzhou Bauxite Deposit, Guangxi Province, China

Mineralogical investigation reveals that diaspore is the main mineral; pyrophyllite, kaolinite, gibbsite and hematite are minor accessories, and rutile is a relict mineral. Diaspore crystallizes in the orthorhombic dipyramidal class and is often associated with kaolinite, pyrophyllite and other clay minerals, and accompanied by hematite. Semi-quantitative XRD results reveal that the modal mineral proportions are diaspore (36.5% 37% ), pyrophyllite (38.60% 46.70% ), kaolinite (6.10% 15.5%), gibbsite (1.6% 3.10%) and hematite (6.60 6.90%) but that these widely in their abundance. The rutile abundance (0.70%) is relatively consistent. The relatively large quantities of silicates decrease A/S ratio and present difficulties for mineral separation.