Gold Mineralization Geochemistry In Muping-rushan Gold Belt,Jiaodong Peninsula,china

Muping-Rushan gold belt is one of the most important gold belts in Eastern Jiaodong Peninsula and quartz sulfide vein type is the main ore type.Comparing to the gold deposits in Northwestern Jiaodong Peninsula,differences occur in some aspects.Combining the previous research,field work and microscopic observation,we performed the hot short-lived CL,in-situ analysis,Ar-Ar dating,in-situ S analysis to study the gold mineralization age,gold precipitation mechanism and origin of ore fluid and ore material in Muping-Rushan gold belt.Previous mineralization age has a wide range,whether mineralization only happened once or several times is uncertain.40Ar-39 Ar dating from Yinggezhuang,Xipo and Sanjia gold deposit yields the result of 120.02±0.38 Ma,121.65±0.48 Ma and 116.51±0.47 Ma,respectively,which shows the mineralization time is within the range of 120±5Ma.The main problem in previous studies on the gold precipitation in Muping-Rushan gold belt is that whether the quartz formed together with gold remains unclear.Mineralogy study shows there are 3 main kinds of pyrite,Pya,Pyb and Pyc,namely,and 5 main kinds of quartz,Qa,Qb,Qc,Qd,Qe,namely.Gold mainly occurs in the fractures of Pyb and quartz.The bearing mineral of fluid inclusions formed before the gold,so fluid unmixing in quartz sulfide vein type gold deposits doesn't apply in Muping-Rushan gold belt.Based on the new paragenesis,the trace element content in different quartz and pyrites were tested to study the gold precipitation mechanism.Al content from EPMA in different types of quartz and the sericite consuming H+ during formation indicate the pH changing during the free gold precipitation.LA-ICP-MS shows the invisible gold mainly occurs as the solid solution in the pyrites.The invisible gold could not be reactivated to form the free gold because the highest invisible gold content is 2ppm.The invisible gold precipitation is involved with surface absorption of pyrites.Previous studies on the origin of ore fluid and ore material has many restraints in the samples and test methods,so we use special sample and in-situ method.Combining the D isotope of sericite and fluid-rock reaction calculation result,the ore fluid in Muping-Rushan gold belt may derive from dehydration of subducting Pacific slab,ore fluid from magmatic fluid and metamorphic fluid of Jiaodong Group were excluded.The insitu S isotope result shows the Jiaodong Group,JingshanGroup and granite wallrock could provide the ore material,but contribute differently to various types of sulfide.Through our study,we draw new conclusions on the paragenesis in Muping-Rushan gold belt and Jiaodong Peninsula,namely the coexisting pyrites and quartz don't form at the same time,and relevant gold precipitation mechanism is proposed based on the paragenesis.We provide new data to the study of mineralization age.More pertinence is employed during the study of origin of ore fluid and ore material.Our study has implications to the regional metallogenesis in Jiaodong Peninsula.