• Mineralization at the Shuangmiaoguan deposit occurred under an extensional regime during the Early Cretaceous. • Visible gold includes native gold, electrum, and petzite, occurring with hessite, naumannite, tellurobismuthite, argentite, matildite, and paderaite. • Invisible gold of a solid solution Au + in pyrites exhibits strong geochemical coupling with Ag, Te, and Bi during the four-stage mineralization. • Addition and immiscibility of deep-sourced magmatic fluids enriched in chalcophile elements (Ag, Te, Bi) controlled Au enrichment. Lode gold deposits account for 40–45% of global gold resources. They are typically formed through precipitation of ore fluids in orogens during compressional to strike-slip setting. Chalcophile elements in the ore fluids can significantly promote the enrichment of gold. However, the mechanism by which this type of ore fluid operates lode gold mineralization in an extensional setting is unclear. This study conducts geological, geochronological, and geochemical analyses on the newly discovered Shuangmiaoguan gold deposit in the Dabie region, south of the North China Craton. Gold mineralization at Shuangmiaoguan can be divided into four stages (Stage 1–Stage 4), and eleven generations of pyrite were identified. Hydrothermal titanites coexisting with pyrite from the major mineralization Stage 3 yield a mean U-Pb age of 127.9 ± 2.7 Ma. It is coeval with the Early Cretaceous detachment event associated with the metamorphic core complex in the Dabie region, indicating that the deposit formed in an extensional setting. Trace element analyses of pyrites from Stages 1–4 reveal the mean Au content from 0.02 to 0.28 ppm, indicating invisible gold of solid solution in this deposit. Positive correlations between Au and Ag, Te, and Bi through the four stages of mineralization reveal that ore fluids are enriched in chalcophile elements. Typical zoning textures of pyrites from Stages 1–3 and their variations in trace elements and δ 34 S suggest that fluid immiscibility developed through the precipitation of visible and invisible gold. The δ 34 S values (with a mean of 0.71‰, 0.06‰, 0.89‰), Co/Ni ratios (> 1), and the contents of chalcophile elements such as Te and Bi in the three generations of Stage 3 pyrites, as well as the homogenization temperature of fluid inclusions in Stage 3 quartz, are considerably higher than those of Stage 2. These lines of evidence reveal the addition of deep-source, high-temperature magmatic fluids enriched in chalcophile elements in the major mineralization Stage 3. Immiscibility of these fluids enriched in chalcophile elements caused significant precipitation of visible gold of native gold, electrum, and petzite in Stage 3, and also the associated hessite, naumannite, tellurobismuthite, argentite, matildite, and paderaite within or along fractures of these pyrites. Significantly decreasing contents of Au and Ag in pyrites, and the appearance of numerous carbonate minerals in Stage 4 mark the termination of mineralization. The proposed model for Shuangmiaoguan highlights that an ore fluid enriched in chalcophile elements controls lode gold mineralization in an extensional setting.
Li et al. (Wed,) studied this question.