Structural geometry and evolution of ore fluid compositions in the Mingshan gold deposit in the Youjiang Basin

• Mingshan gold deposit controlled by low-angle imbricate thrust faults. • Elevated δ 34 S values from pyrite core to rim caused by fluid-rock interactions. • Ore materials derived from deep source regions with wall rock contamination. Structural controls and ore fluid compositions in the Mingshan gold deposit in the Youjiang Basin remain poorly understood. Structural geometry, mineral assemblage, sulfur isotopes, and trace elements in this deposit were studied to resolve using field structural geological surveys, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and in situ sulfur isotope analysis. Structural investigation indicates that the gold ore bodies hosted in the Middle Triassic turbidites are controlled by NW- to NWW-trending low-angle imbricate thrust faults formed under N-S-oriented compression, and are subsequently cut by NE-trending strike-slip faults. Three stages of gold mineralization were identified, including quartz-pyrite (stage I), pyrite-arsenopyrite-quartz (stage II), and polymetallic sulfide-calcite (stage III). The pyrite comprises framboidal pyrite (Py1) and zonal hydrothermal pyrite, including the gold-arsenic-poor porous core (Py2), the arsenic-rich bright mantle (Py3), and the gold-rich rim (Py4). In situ sulfur isotope analysis reveals δ 34 S values ranging from +3.1 to +15.1 ‰ for Py1, −8.5 to −2.4 ‰ for Py2, −8.0 to −0.8 ‰ for Py3, and −3.1 to 0.8 ‰ for Py4. The hydrothermal pyrite sulfur isotope composition and an increase in δ 34 S values from core to rim show that ore-forming materials originate from deep source regions but are contaminated by wall rock via fluid-rock interactions. The imbricate thrust-controlled gold ore systems not only enhance our knowledge of structural deformation characteristics and metallogenic mechanisms but also provide important clues for regional prospecting and exploration.