Minerals

The Yawan gold deposit, located in the Western Qinling Orogen, contains gold mineralisation that is predominantly controlled by approximately east-west-trending fault systems. This study integrates field geology, petrography, cathodoluminescence imaging, electron probe microanalysis of gold-bearing minerals (pyrite and arsenopyrite), and in situ laser ablation U-Pb dating of calcite to constrain the timing of mineralisation and to elucidate the mechanisms of gold enrichment. This study reveals that the deposit is significantly structurally controlled and comprises two discrete mineralisation stages: a quartz-pyrite (Py1)-arsenopyrite (Apy1)-chalcopyrite assemblage (Stage 1), and a quartz-calcite-pyrite (Py2)-arsenopyrite (Apy2)-stibnite-sphalerite-galena assemblage (Stage 2). Py1 displays distinct zonation, with rim As contents notably higher than core values, while Co and Ni contents gradually decrease from core to rim. Py2 is characterised by high As (0.00%–4.72%), low Fe/S ratios, and a porous texture, containing gold and arsenopyrite inclusions. Invisible gold occurs in lattice-bound form in both Py1 and Py2. The As-Fe-S ternary diagram of pyrite indicates that Au⁺ likely entered the crystal lattice as a solid solution. Arsenopyrite geothermometry yields a mineralisation temperature of 389 ± 44 °C, and sulfur fugacity (ƒS₂) decreased markedly from Stage 1 to Stage 2. Combined with the S and Fe characteristics of pyrite, these features support a medium-temperature metamorphic hydrothermal environment. U-Pb dating of calcite from Stage 2 yields an age of 215.6 ± 7.1 Ma. In summary, the Yawan gold deposit belongs to the orogenic gold system, with its gold precipitation and enrichment controlled by sulfidation triggered by Late Triassic tectono-fluid activity.

Coal and its associated minerals are vital geological resources, holding significant value for both energy security and the supply of strategic materials [...]

In magnetic separation processes, the capture radius R_c of magnetic particles achieved by the magnetic matrix constitutes a critical parameter governing the separation efficiency and operational performance of magnetic separation equipment. Through a systematic study of the characteristics of R_c and the factors influencing it, the application capability of separation systems can be notably improved. To address the lack of systematic research on R_c under low magnetic field intensities (<0.6 T), a key gap compared to conventional high gradient magnetic separation (HGMS) operating at ≥0.6 T, the motion trajectories of magnetic particles adjacent to a rod-shaped matrix, as well as their final capture or repulsion behaviors, were observed via a high-speed camera. Concurrently, these processes were accurately reproduced using the finite element method (FEM). This study innovatively integrates experimental validation and FEM simulation, achieving mutual verification that single-method studies cannot provide. Based on the experimentally validated FEM model, the effects of magnetic field intensity H, rod-shaped matrix diameter Φ, magnetic particle diameter d, and fluid viscosity η on the motion of magnetic particles were methodically investigated. The velocity characteristics of particles at critical positions between the capture and repulsion zones were analyzed to determine the capture radius of the rod-shaped matrix under specified conditions. Drawing on the identified parametric effects, the developed capture radius prediction model fills the research gap in low-intensity HGMS and serves as a theoretical reference for optimizing both the spacing design of industrial-scale rod-shaped matrix arrays and their matching with relevant operating parameters, and the development of energy-efficient magnetic separation equipment.