As is widely accepted, cumulative strain and improvement mechanisms of stabilized soil are critical factors for the long-term reliable operation of expressways and high-speed railways. Based on relevant research findings, xanthan gum biopolymer is regarded as a green and environmentally friendly curing agent in comparison to traditional stabilizers, such as cement, lime, and fly ash. However, little attention has been devoted to the cumulative strain and improvement mechanisms of soil reinforced by xanthan gum biopolymer under traffic loading. In the current study, a series of laboratory tests, including cyclic triaxial tests and scanning electron microscopy (SEM) tests, were performed to investigate this issue in more detail. The influences of xanthan gum biopolymer content, curing time, moisture content, confining pressure, and cyclic stress amplitude on cumulative strain were analyzed. In addition, the cumulative strain model was proposed to provide a good description of experimental data. Finally, the microscopic structure of soil reinforced by xanthan gum biopolymer was analyzed to discuss the improvement mechanisms. The results show that the cumulative strain is strongly influenced by xanthan gum biopolymer content. For a given number of loading cycles, the greater the confining pressure, the smaller the cumulative strain. The calculated results of the cumulative strain model show a good agreement with test data. The “flocculent” hydrogel can form a denser structure and greater bonding strength in comparison to the “branch-like” and “net-like” hydrogels.

The Jiepailing deposit in southern Hunan is a typical large to super-large polymetallic tin deposit enriched in beryllium and other rare metals. To enhance the understanding of the mineralization processes of the Jiepailing deposit, detailed mineralogical, in situ geochemical, and sulfur isotopic analyses were conducted on pyrite closely associated with tin–polymetallic mineralization. Five types of pyrite have been identified in the deposit: (1) euhedral to subhedral medium- to coarse-grained pyrite (PyI) in tungsten–tin ore; anhedral fine-grained pyrite (PyII) in tin polymetallic–fluorite ore; anhedral fine-grained or aggregate pyrite (PyIII) in lead–zinc ore; euhedral to subhedral coarse-grained pyrite (PyIV) in beryllium–fluorite mineralization; and subhedral to anhedral fine-grained pyrite (PyV) in carbonate veinlets developed in the wall rock. Backscattered electron imaging indicates consistent structural features across the five types of pyrite. In situ trace element analysis reveals differences in trace element concentrations among the pyrite types. PyI is relatively enriched in Sn, Cu, and Co. In contrast, PyIII is enriched in Pb, Zn, Sn, and Ti, while PyIV and PyV are enriched in Ag and Sb. PyI has a Co/Ni ratio more than 1, while the Co/Ni ratios in the other four types of pyrite are less than 1. LA-MC-ICP-MS in situ sulfur isotope analysis shows δ³⁴S values ranging from 2.5‰ to 5.8‰ (average 4.3‰, PyI), 2.5‰ to 5.8‰ (average 4.3‰, PyII), −7.6‰ to 9.5‰ (average 3.9‰, PyIII), −3.7‰ to 10.6‰ (average 3.6‰, PyIV), and 6.8‰ to 14.1‰ (average 9.2‰, PyV). Based on previous studies, regional geological background, deposit characteristics, and the in situ trace element and sulfur isotope compositions of pyrite, it is inferred that the various ore bodies in the Jiepailing deposit are products of Late Cretaceous magmatic–hydrothermal activity. The early ore-forming fluid originated from magmatic sources and during the migration into the wall rock and shallow formations, mixed with fluids primarily derived from atmospheric precipitation. Temperature, pressure, and composition changed of the ore-forming fluid which carried a large amount of substances, leading to tungsten–tin, tin polymetallic–fluorite, lead–zinc, and beryllium–fluorite mineralization, followed by carbonation during the late-stage mineralization.

Tungsten (W) has recently gained recognition as a potentially powerful tool for reconstructing palaeo-oceanic conditions, yet its enrichment mechanisms in sulfidic environments remain poorly constrained. Here, we investigate W cycling in sulfidic sediments from the Haima Cold Seep (South China Sea), revealing a paradoxical decoupling of low W concentrations and high enrichment factors (WEF), which we attribute to pyrite-mediated W sequestration. Sulfidation promotes pyrite formation and Fe-Mn (hydrogen)oxides dissolution. Inadequate W uptake by pyrite causes low bulk W content, yet the high (Wpy)EF can elevate the bulk sediment WEF, thereby producing the decoupling between low W content and high WEF in the sediment. Furthermore, varying environmental sulfidic levels drive aqueous W speciation, affecting subsequent pyrite adsorption and leading to differences in pyrite W content and WEF. This study significantly enhances our understanding of the W cycle in sulfidic marine environments.