Mineral paragenesis and ore-forming process of the large Xiaoyingpan Te-rich gold deposit, North China Craton: Insights from deposit geology and pyrite geochemistry

• The first detailed study of mineral paragenesis and ore-forming process at Xiaoyingpan Te-rich Au deposit. • Three mineralization paragenetic stages corresponding to three pyrite generations were recognized. • Changing in physicochemical conditions and intensity of fluid boiling controlling the occurrence of Au and Te at Xiaoyingpan. • Te-rich metallic melts is alterative mechanism for Au and Te enrichment. Quartz vein-type gold deposits in the North China Craton form the world’s third-largest gold province. Although widely studied, the Xiaoyingpan Te-rich Au deposit in the Zhang-Xuan district remains not well understood regarding mineral paragenesis and ore-forming processes. This study conducts an integrated analysis of deposit geology, pyrite microtextures, in-situ trace element, and sulfur isotope (δ 34 S) compositions to elucidate these aspects. Field observations and petrographic examinations reveal three distinct mineralization paragenetic stages associated with three generations of pyrite (Py-1, Py-2, Py-3). These three pyrite generations have comparable Au, Ag, Te, Bi, and Cu contents, while Py-1 exhibits distinct Co and As enrichment. Bi contents across three pyrite generations are mainly below the detection limit indicating a minimal Bi availability in ore fluids. Microtexture and geochemical compositions suggest Au occurs as lattice-bound solid solutions and submicroscopic nanoparticles in Py-1, which correlates with the absence of visible native gold in stage I. In contrast, Au in the stage II and III exhibit three occurrence patterns, including lattice-bound, nanoparticle, and visible micro-scale grains (mostly 1–50 μm in size). Similarly, As-Te plotting combined with petrographic analyses indicates that Te is mainly bounded within Py-1 structure, whereas it occurs as solid solution and micro- to nano-scale particles in Py-2 and Py-3. Negative δ 34 S values are suggestive of fluid oxidization. Based on these integrated analyses, we propose that Py-I formed under realtively high-temperature, oxidized, alkaline conditions with gentle boiling, which promoted Te solubility and limited Au solubility in liquid-rich fluid systems. The incorporation of Te and Au into Py-1 as solid solution is mainly controlled by high As contents in ore fluids. In contrast, Py-2 and Py-3 formed under relatively acid to neutral, reduced conditions with vigorous fluid boiling. This would destabilize of Au(HS) 2 – and HTe 2 – and trigger their precipitates. Smoothboundaries between tellurides and native gold, along with high mineralization temperatures, suggest the deposition of polymetallic Te-rich melts that scavenged Au from ore fluids., accounting for the enrichment of Au and Te in stages II and III.