Sphalerite Rb-Sr Dating and in situ Sulfur Isotope Analysis of the Daliangzi Lead-Zinc Deposit in Sichuan Province, SW China

This study reports the sphalerite Rb-Sr age and LA-MC-ICP-MS in situ sulfur isotope analysis results of the Daliangzi Lead-Zinc Deposit in the Sichuan-Yunnan-Guizhou (SYG) triangle. Sphalerite Rb-Sr dating yields a Mississippian age of 345.2±3.6 Ma (MSWD=1.4), which is older than the published Late Triassic mineralization ages (230‒200 Ma) of some other deposits. This indicates that at least two stages of lead-zinc mineralization have occurred in the SYG lead-zinc triangle. The first stage occurred in the Mississippian under an extensional environment, while the second stage occurred in the Late Triassic under a compressional environment. In situ sulfur isotope analysis of sphalerite growth zoning presents relatively large δ 34 S values of 11.3‰‒15.2‰ with small variations. The large δ 34 S values indicate a reduced sulfur source of thermochemical reduction of seawater sulfates. Abundant organic matter in the black fracture zone possibly supplied reductants for thermochemical sulfate reduction (TSR) at the mineralization site. The small variation of δ 34 S values suggests a slow and stable TSR process that could prevent the sudden supersaturation of sphalerite in the fluid and the resulting of fast participation. This is consistent with the well-crystallized characteristic of the sphalerite of the Daliangzi Deposit.