Research On Ore-forming Fluid And Stable Isotopes In Xingjiashan Molybdenum Deposit,shandong Province

The Qixia-Penglai-Fushan is an important polymetallic metallogenic belt during the Mesozoic period in Jiaodong Peninsula.The Xingjiashan skarn-type Mo deposit is one of the typical examples as late Jurassic metallogenisis in eastern Shandong.In this thesis,we discuss the geological characteristics,resources and evolution of ore-forming fluids,ore-forming material and metallogenic mechanism based on the fluid inclusions,C-H-O-S isotopes,especially molybdenum isotope.The main achievements are as follows:?1?Ore bodies are hosted in the metamorphic strata in the external contact zone of Xingfushan Pluton.The ore types are skarn and quartz metal-sulfide vein types.The metallogenic stage could be divided into four stages:early skarnization stage???with tungsten mineralization,late skarnization???and quartz metal-sulfide vein stages???with molybdenum mineralization,and quartz-carbonate stages???.?2?Types of fluid inclusions comprise single-phase vapor or liquid inclusion?V or L type?,two-phase vapor-liquid inclusion?LV type?and halite-bearing three-phase inclusion?LVS type?.Homogeneous temperature and salinity of ore-forming fluid are293.5-532.6?and 6.2-61.5%NaCleqv in stage?,271.0-502.0?and3.6->36.0%NaCleqv in stage?,154.1-580.0?and 0.2-53.0%NaCleqv in stage?,73.4-358.0?and 0.4-11.5%NaCleqv in stage?.They are characteried by high homogeneous temperature and salinity.Fluid inclusions have CO,CO₂ and H₂S,indicating the ore-forming fluid belonged to the high temperature and salinity NaCl-H₂O?-CO-H₂S?fluid system,and evolved into the NaCl-H₂O fluid.?3?Hydrogen and oxygen isotopic compositions indicate ore-forming fluid was derived from magmatic water in the quartz metal-sulfide vein stage with mixture of minor meteoric water.Compositions of carbon,sulfur and molybdenum isotopes indicate the deep magmatic source of ore-forming materials with minor stratigraphic sulfur and molybdenum.The fluid boiling in the late skarnization stage was major reason for the sedimentation of metallogenic materials,and the meteoric water promoted mineral precipitation.?4?During the middle-late Jurassic,the subduction of ancient Pacific plate beneath the North China plate resulted in remelting of lower crust.The magma of remelting crust migrated along fault,and formed the Xinfushan Pluton.The immiscibility of initial magmatic fluid formed high temperature and salinity NaCl-H₂O?-CO-H₂S?fluid.The boiling of fluid made the ore-forming materials precipitating in the contact zone,structural fracture zone and the inter-stratigraphic slip space,formed the molybdenum ore bodies.