Yin Gong

The upper Permian Dalong Formation in western Hubei Province is a crucial strategic successor for shale gas development in South China. However, the geological controls on reservoir pore development, particularly the influence of organic–inorganic interactions on the pore system, remain poorly understood. This restricts the precise optimization of shale gas exploration targets in this formation. To investigate the pore development characteristics and main controlling factors of the Dalong Formation shale reservoirs, this study takes the DFS from the Shuanghe section in western Hubei as the research object. X-ray diffraction (XRD), argon-ion polishing-scanning electron microscopy (SEM), and N₂/CO₂ gas adsorption–desorption technologies were integrated to achieve qualitative characterization and quantitative assessment of the pore network, with analyses of pore size distribution. The results show that the pores of the DFSs are dominated by interparticle pores and organic matter pores, and the pore structures of organic-rich and organic-lean shales exhibit significant differentiation characteristics. The quartz in the DFSs are mainly of diagenetic origin, and authigenic quartz cementation blocks primary intergranular pores, exerting a significant negative effect on pore development. In contrast, the smectite-to-illite transformation promotes the development of interlayer micropores, leading to a good positive correlation between clay mineral content and micropore volume, as well as specific surface area. Organic matter abundance is the core controlling factor for the construction of micro–nano pore networks. This study clarifies the dominant mechanisms of pore development driven by organic–inorganic interactions in the DFS. Authigenic diagenetic quartz impedes pore development, while smectite-to-illite transformation promotes micropore formation. Organic matter abundance is the dominant control on the micro-nanopore system. This study lays a critical geological theoretical foundation for the exploration evaluation and target selection of shale gas in the Dalong Formation.

Marine black shales are important to geologists, because they are not only potential sources and reservoir rocks for shale gas/oil, but also, their deposition could influence the climatic and oceanic environments. Here, a detailed study of the shales in the Dalong Formation in South China was conducted to understand the changes in continental weathering and upwelling and their influences on organic matter accumulation in the late Permian. The results revealed that the deposition of the Dalong and Daye Formations could be divided into five stages, with the highest TOC values (>2%) being observed in stages 2 and 4, intermediate TOCs (~1% to 2%) being observed in stages 1 and 3, and the lowest TOC values (26Mg values) and intense upwelling (high Mo/TOC ratios and low δ¹³C_org and Co_EF × Mn_EF values), both of which contributed to high primary productivity and increased anoxia of the bottom waters, further leading to the accumulation of organic matter. Overall, both enhanced continental weathering and upwelling contributed to the development of anoxia, even euxinia, of the seawater and further triggered an end-Permian mass extinction (EPME).

With the increasing demand for lithium (Li) resources in industry, there has been new attention on clay-type lithium-rich deposits recently. In this study, a Li-rich clay deposit with a Li₂O content up to 0.3% in the Liangshan Formation in the upper Yangtze, South China Block was demonstrated. We analysed the mineralogy and element geochemistry of the samples from the Liangshan Formation and its underlying and overlying layers. Kaolinite (average 53%, up to 93%) was the major mineral in the samples from the Liangshan Formation. The Li concentrations increased with increasing kaolinite compositions and Al₂O₃ concentrations. Furthermore, based on the geochemical indicators, it was suggested that the clay formation and Li enrichment were related to the weathering processes of the bottom impure limestone under the hot and wet climate, and the sedimentary processes in the anoxic, still, and flat land–sea interaction area in the Upper Yangtze. The Li was probably sourced from the bottom impure limestone during the weathering stage. The samples from the Liangshan Formation also showed REE enrichment from 117 to 729 μg/g.

The Mahuagou gold deposit is among the most important gold deposits in the core of the Huangling Anticline. However, the geochemical exploration on the surface of the mining area presents challenges due to the thin overburden. This paper focuses on the overburden soil of the Fengxiangshugou (FXS)-Mahuanggou (MHG) section as the research object. It utilizes chemical form analysis of gold, soil halogen survey, and heat-released mercury survey to determine the key deep-penetrating geochemical methods for the mining area. The results indicated that Si and Al components of samples exhibit minimal variation, suggesting that drift loads did not influence the overburden soil. Based on the systematic clustering, As, Sb, Mo, Bi, W, and Hg emerge as ore-body or ore-belt front elements of hydrothermal gold deposits. In the study area, the predominant chemical form of gold in soil is the strong organic bond. Compared to the total amount, strong organic bound gold and heat-released mercury show higher anomaly contrasts, making them crucial indicators of faults, intrusions, and hidden ore bodies. Consequently, chemical form analysis of gold and heat-released mercury surveys can enhance the anomaly contrast, proving beneficial for geochemical prospecting for weak anomalies in this area.

The Mahuagou gold deposit is among the most important gold deposits in the core of Huangling Anticline. However, the geochemical exploration on the surface of the mining area presents challenges due to the thin overburde.This paper focuses on the overburden soil of Fengxiangshugou (FXS) – Mahuanggou (MHG) section as the research object, utilizes chemical form analysis of gold, soil halogen survey, and heat-released mercury survey to determine the key deep-penetrating geochemical methods for mining area. The results indicated that Si and Al components of samples exhibit minimal variation, suggesting that drift loads did not influence the overburden soil. Based on the systematic clustering, As, Sb, Mo, Bi, W and Hg emerge as ore-body or ore-belt front elements of hydrothermal gold deposits. In the study area, the predominant chemical form of gold in soil is the strong organic bond. Compared to the total amount, strong organic bound gold and heat-released mercury show higher anomaly contrasts, making them crucial indicators of faults, intrusions and hidden ore bodies. Consequently, chemical form analysis of gold and heat-released mercury surveys can enhance the anomaly contrast, proving beneficial for geochemical prospecting for weak anomalies in this area.