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Mesozoic volcanic rocks are widespread throughout the Great Xing'an Range of northeastern China. However, there has been limited investigation into the age and petrogenesis of the Mesozoic volcanics in the eastern Great Xing'an Range. According to our research, the volcanic rocks of the Dayangshu Basin, eastern Great Xing'an Range are composed mainly of trachybasalt, basaltic andesite, and basaltic trachyandesite, with minor intermediate-basic pyroclastic rocks. In this study, the geochemistry and geochronology of the Mesozoic volcanic rocks are presented in order to discuss the petrogenesis and tectonic setting of the Ganhe Formation in the Dayangshu Basin. Zircon U-Pb dating by laser ablation inductively coupled plasma-mass spectrometry indicates that the Mesozoic lavas formed during the late Early Cretaceous (114.3-108.8 Ma). This suite of rocks exhibits a range of geochemical signatures indicating subduction-related genesis, including: (i) calcalkaline to high-K calc-alkaline major element compositions; (ii) enrichment of large ion lithophile elements (e.g. Rb, Ba, K) and light rare earth elements (LREEs/HREEs =7.33-9.85); and (iii) weak depletion in high field strength elements (e.g. Nb, Ta, Ti). Furthermore, Sr-Nd-Pb isotopic data yield initial 87 Sr/ 86 Sr values of 0.70450-0.70463, positive ε Nd (t) values of +1.8 to +3.3, and a mantle-derived lead isotope composition. Combined with the regional tectonic evolution, the results of this study suggest that the Ganhe Group lavas are derived from decompression melting of a metasomatized (enriched) lithospheric mantle, related to asthenospheric upwelling, which resulted from lithospheric mantle delamination and produced extension of the continental margin following the subduction of the Paleo-Pacific Plate.

A number of sediment-hosted, Carlin-type/-like gold deposits are distributed in the Youjiang basin of SW China. The gold ores are characterized by high As, Hg, and Sb contents but with low base metal contents (Cu+Pb+Zn < 500–1000 ppm). The Nibao deposit is unique among these gold deposits by having tennantite–tetrahedrite-series minerals in its ores. The deposit is also unique in being primarily hosted in the relatively unreactive siliceous pyroclastic rocks, unlike classic Carlin-type gold deposits that are hosted in carbonates or calcareous clastic rocks. In this study, we have identified tennantite-(Zn), tennantite-(Hg), and tetrahedrite-(Zn) from the tennantite–tetrahedrite-series mineral assemblage. The tennantite-(Zn) can be further divided into two sub-types of Tn-(Zn)-I; and Tn-(Zn)-II;. Tn-(Zn)-I; usually occurs in the core of a Tennantite–tetrahedrite composite and appears the darkest under the SEM image, whereas Tn-(Zn)-II overgrows on Tn-(Zn)-I and is overgrown by tetrahedrite-(Zn). Tennantite-(Hg) occasionally occurs as inclusions near the uneven boundary between Tn-(Zn)-I and Tn-(Zn)-II. An appreciable amount of Au (up to 3540 ppm) resides in the tennantite–tetrahedrite-series minerals, indicating that the latter is a major Au host at Nibao. The coexistence of tennantite–tetrahedrite-series minerals and Au-bearing pyrite indicates the Nibao ore fluids were more oxidized than the Carlin-type ore fluids. The tennantite–tetrahedrite series at Nibao evolved from Tn-(Zn)-I through Tn-(Zn)-II to tetrahedrite-(Zn), which is likely caused by Sb accumulation in the ore fluids. This indicates that the Nibao ore fluids may have become more reduced and less acidic during Au precipitation.

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Abundant Cu and Mo deposits are spatially related to granitic complexes in the Nuomin area, eastern Da Hinggan Mountains, China. The petrogenesis of these deposits is investigated using data from zircon U–Pb dating, whole‐rock major and trace element geochemistry, and Sr–Nd–Pb isotopic compositions. The results show that the fine‐grained biotite monzogranite and medium‐grained biotite syenogranite formed in a Late Jurassic (155.7 ± 3.6 Ma) collision environment, characterized by fluid–melt interaction and plagioclase differentiation. These rocks belong to the high‐K calc‐alkaline, K‐peraluminous series, indicating that the parent magma evolved from the low‐temperature partial melting of lower crust, with geochemistry consistent with Neoproterozoic oceanic crust. The monzonitic diorite porphyrite, monzonite porphyry (with a crystallization age of 130.64 ± 0.74 Ma) and quartz monzonite porphyry belong to the high‐K calc‐alkaline, sodic, quasi‐aluminous series. The results indicate petrogenesis in a post‐collisional or late‐orogenic tectonic environment, characterized by interactions with CO2‐rich fluid and the fractional crystallization of amphibole, biotite and apatite. The parent magma formed from the partial melting of residual Neoproterozoic oceanic crust. The circulation of mineralized fluids was related to the petrogenesis of the monzonitic diorite porphyrite, monzonite porphyry and quartz monzonite porphyry. Copyright © 2015 John Wiley & Sons, Ltd.

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