Cherts have been thought to originate from biosilicification, terrestrial inputs and hydrothermal activity. The study of cherts is helpful in understanding the paleo-ocean environment and tectonic–sedimentary processes. Large amounts of cherts occur widely in the Maokou Formation in the Sichuan Basin, which may be largely connected to the Permian Chert Event (PCE). However, the source of silica and the formation process of cherts remain debated. Here, we analyze the petrographic and geochemical features of the cherts from the Guadalupian Maokou Formation (~268–259 Ma) in six sections in the Sichuan Basin. Two main types of cherts, nodular and bedded, are recognized in the Maokou Formation. The formation of nodular cherts was mainly affected by hydrothermal fluids, whereas the bedded cherts are mainly of biogenetic origin. The Emeishan large igneous province (ELIP) caused the activation of deep faults, accompanied by intense hydrothermal activities. Correspondingly, the cherts of significant hydrothermal origin developed near the active deep faults. The intensified hydrothermal activities may provide extra silica supplies and flourish the silica-secreting organisms by the associated volcanogenic upwellings that facilitated the enrichment of cherts. The study of Maokou cherts can help to record the volcanic- and silicon-related biological activities in the eastern Paleo-Tethys Ocean and can provide significant implications for chert enrichment in analogous settings.

Dolomite bodies in the Middle Permian of the central Sichuan Basin have been reported as favorable natural gas reservoirs. The Middle Permian dolomite consists of three types of recrystallized dolomite (Rd1, Rd2, and Rd3) and one type of dolomite cement (Sd). Rd1 might be formed as the primary mineral along the calcite in the original sea-water. Its δ¹³C value and ⁸⁷Sr/⁸⁶Sr ratio, consistent with those of marine limestone and Permian seawater, support that the dolomitizing fluid for Rd1 was Permian seawater preserved in the strata. Rd2 consists of fine to medium (50 μm to 250 μm) and planar to curved crystals. Geochemical indicators (slightly high ⁸⁷Sr/⁸⁶Sr ratio, similar rare earth element patterns, negative δ¹⁸O, slightly high salinity) confirm that the dolomitizing fluid of Rd2 was mainly Permian seawater during shallow burial, with a small number of hydrothermal fluids. Rd3 and Sd are featured by very large (>250 μm), curved crystals, and high-temperature, high-salinity, and obviously positive Eu anomalies, suggesting that their diagenetic fluids were mainly hydrothermal fluids from deep. Additionally, inherited carbon sources and the ⁸⁷Sr/⁸⁶Sr ratios of some samples fall within the range of Permian seawater distribution, confirming the contribution of Permian seawater. ELIP activity caused the formation of this dolomite through the mixing of seawater and hydrothermal fluids. The main fluid circulation channels were activated basement faults, epigenetic karst pores, and shallowly buried high-permeability strata. During the peak period of ELIP activity, the continuous upwelling of deep hydrothermal fluids led to the continuous formation of Rd2, Rd3, and Sd. The dolomitization fluid of Rd2 was mainly composed of seawater and featured a certain lateral extension, which was away from faults. Rd3 and Sd are mainly distributed along the fault system, and excessive dolomitization caused by the hydrothermal activity, to some extent, inhibited the lateral movement of hydrothermal fluids. This study provides a good example for exploring the genetic mechanism and distribution pattern of structurally controlled dolomites under a volcanic activity background.

Red mud, a hazardous industrial waste generated during alumina production, faces great challenges in safe stacking and utilization due to its complex chemical composition and poor engineering properties. Long-term stacking of red mud is accompanied by repeated natural drying-wetting cycles, which significantly alter its strength characteristics and further threaten the stability of red mud stockpiles. In this study, Bayer red mud (BRM) and mixed red mud (MRM) from the No.5 stockpile of Guizhou Aluminum Plant were tested under 0, 1, 3, 7, 12 drying-wetting cycles. Their physical, microscopic, and mechanical properties were investigated. Stockpile stability under extreme rainfall was evaluated using Geo-Studio software (SEEP/W and SLOPE/W modules). The results showed that unconfined compressive strength (q_u) and cohesion (c) of BRM decrease with cycles, while those of MRM increased significantly. Specially, the (q_u) of MRM rise from 115.78 kPa to 150.38 kPa and the cohesion (c) doubles from 61.67 kPa to 121.91 kPa. The internal friction angle (φ) of BRM increases slightly, while that of MRM decreases slightly. Under extreme rainfall conditions, safety factors of red mud are 1.205, 1.219, 1.240, 1.263 and 1.288, respectively, all greater than the critical value of 1.0 and increasing with cycles. This study demonstrates that stacking MRM on BRM is feasible and effective for improving the long term stockpile stability, which provide theoretical support and engineering guidance for the safe stacking and resource utilization of red mud.