Abstract The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered (from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn‐ or porphyry–skarn‐type deposits; however there have been recent discoveries of numerous vein‐type Au, Ag, and Pb‐Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore‐controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits (skarn‐, porphyry‐, and vein‐type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore‐forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry‐, skarn‐, and vein‐type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep‐seated and concealed porphyry‐type Cu (–Mo, –Au) deposits as well as shallow vein‐type Au, Ag, and Pb–Zn deposits in this area and elsewhere.
The Chating Cu–Au deposit is an important porphyry deposit located in the Middle–Lower Yangtze River Metallogenic Belt (MLYMB) of eastern China. Drill core logging and ore petrographic observations were systematically employed to recognize the geological features of the deposit. Several important and peculiar geological characteristics are revealed as fellows: (1) the ore-bearing quartz diorite porphyry emplaced within carbonate-dominated strata rather than clastic strata and volcanic rocks, (2) the ore-hosting location confined in the whole cryptoexplosive breccia pipe inside the porphyry stock, and (3) large-scale and barren marbles, marbled limestones, and hornfels almost encircling the porphyry stock and sporadic and barren skarns scattered within the porphyry stock. The fluid-inclusion study at the deposit reports a wide range of homogenization temperatures (161.4 °C–454.2 °C) and salinities (0.2–54.7 wt% NaCl eq) for the ore-forming fluids, and two fluid boiling events as suggested by the coexistence of halite-bearing liquid-rich inclusions and vapor-rich inclusions. In contrast with classical porphyry deposits, the Chating deposit has similar characteristics in the close relationships between the mineralization and the porphyry stock, the hydrothermal alteration zonation, and the fluid evolution process, while the wall-rock strata and ore-hosting position mark outstanding differences of the Chating deposit. The comprehensive geological and geochemical research in this study has been integrated to explore the ore-forming mechanisms of the deposit. The carbonate wall-rock strata were baked by early magma to form low-permeability thermal metamorphic shield at the contact zone, which prevents the migration and loss of the ore-forming fluids and avoid hydrothermal metasomatism for skarn ores. After that, the cryptoexplosions open up the porphyry system and promote the magmatic hydrothermal fluids mixing with the meteoric water, which successively induce the ore-forming fluids boiling and further cause ore-forming materials unloading and precipitation in the cryptoexplosive breccia pipe.
To date, the types of fuels used in pottery kilns during the Western Zhou Dynasty have not been adequately addressed. Samples from updraft kilns and semi-downdraft kilns at the Fengjing site, the capital in the late Western Zhou period, were selected for analysis. Through phytolith and wood charcoal analysis, various grasses mainly Panicoideae, Pooideae, and Eragrostidoideae, as well as millet, rice, and wheat crops were identified. Additionally, wood primarily from trees of the Quercus, Ulmus, and Liquidambar taxa was found. These findings suggest that different pottery kilns used similar fuels, demonstrating a broad-spectrum rather than specialized fuel utilization during the Zhou period.
In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even < 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even < −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.
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