Abstract: The Yangshan gold belt is the largest isolated gold deposit district in the West Qinling gold belt, where disseminated mineralization is dominant with lesser quartz vein type mineralization. Native visible gold and “invisible gold” are both developed in the gold belt, making the Yangshan gold belt ideal for studying gold occurrence in orogenic gold deposits. Such study is significant for understanding gold metallogeny and ore-forming processes and beneficial for guiding mineral processing. Based on detailed field investigation and micro-observations, the ore paragenesis can be divided into early (pyrite-quartz), main (pyrite-arsenopyrite-sericite-quartz) and late (stibnite-quartz-calcite) ore stages. We used a combination of electron microscope, laser ablation inductively coupled plasma mass spectrometry, inductively coupled plasma mass spectrometer, high resolution transmission electron microscopy and X-ray powder diffraction to investigate gold occurrence in different ore stages. We further discussed the implications of the gold occurrence in the ore-forming processes in the Yangshan gold belt. The results show that the early and main ore stage mineralization is dominated by micro-grained disseminated sulfides and gold occurs as lattice gold in pyrite and arsenopyrite, whereas vein type mineralization is dominated in the late ore stage and gold occurs as native visible gold. The changing of gold occurrence indicates that, from early to late ore stages, fluid temperature and pressure decreased gradually and the ore fluid evolved from As-rich to relatively As-poor and Sb-rich fluid.

Key words: gold occurrence, LA-ICP-MS, HRTEM, XRD, Yangshan, West Qinling