The Ore- Forming Fluid And Mineralization Of Epithermal Gold Deposits In Pinyi, Western Shangdong

Located tectonically on the southeastern margin of the North China craton, telluride Au deposits in the Pingyi area, western Shandong, mainly comprise the cryptoexplosive breccia type Guilaizhuang gold deposit and stratified, finely disseminated type Mofanggou gold deposit in carbonate rocks. The Guilaizhuang gold orebodies, hosted in Cambrian-Ordovician dolomite, are controlled by EW-trending fault. Inside the fault zone, orebody No. I is largest, contributing 98% of the total ore reserves of the Guilaizhuang gold deposit. It has a controlled length of 550 m long, a thickness of 3.3–10.1m (mean 6.8 m) and a dip width of >650 m. Drilling has revealed that the ore vein pinches and swells and branches and converges. The gold grade ranges from 3.42 to 26.37 g/t, with a mean of 6.8 g/t and a maximum of 457.4 g/t. The Guilaizhuang gold orebodies are lithologically composed of cryptoexplosive breccia, which comprised diorite (porphyry) and monzosyenite porphyry from Tongshi complex and minor clasts of Cambrian-Ordovician dolomite. Gold minerals mainly include native gold, electrum and calaverite. The Lifanggou and Mofanggou gold deposits occur as bed-like bodies in dolomitic limestone, micrite and dolostone in the Early Cambrian Zhushadong Formation. The orebodies are about 20–30m from the unconformity between Cambrian carbonate rocks and Neoarchean biotite leptite or Paleoproterozoic monzogranite. The Lifanggou ore bed is generally 3–10 m in thickness and controlled by NW-trending secondary detachment faults, whereas Mofanggou gold bed dipping 325°–350°at 8–20°in the Early Cambrian Zhushadong Formation.is ca. 280 m long and 1.0–8.0 m thick. The Lifanggou gold grade ranges from 2.19 to 7.24 g/t, with a mean of 4.9g/t, and Mofanggou gold grade from 1.09 to 25.21 g/t, with a mean of 11.54g/t. Wall-rock alteration comprises pyritization, fluoritization, silicification, carbonatization and chloritization. The Tongshi complex related to mineralization in the ore districts consists predominantly of medium-to fine-grained diorite (porphyry) and pyroxene (hornblende)-bearing monzonite porphyry. Zircon SHRIMP U-Pb dating indicates that the dioritic rocks of the Tongshi magmatic complex give a 206Pb/238U weighted mean age of 175.7±3.8 Ma, interpreted as representing the crystallization age of the Tongshi magmatic complex. The Guilaizhuang, and Mofanggou gold deposits are telluride gold deposits related to alkaline rocks. Therefore, it is reasonable to infer that the age of the gold deposits was Middle Jurassic. Nearly 300 fluid inclusions were examined in 18 samples from the Lifanggou, Mofanggou and Guilaizhuang gold mines. Abundant fluid inclusions were observed in quartz, calcite and fluorite. They are dominated by primary ones with minor pseudosecondary ones.