The Diagenesis And Metallogeneses Studies On Yuanzhuding Porphyry Cu-Mo Deposit In Guangdong

The Yuanzhuding Cu-Mo porphyry deposit with a Cu and Mo resources of0.98Mt and0.26Mt, is located at Fengkai County of Guangdong Province and occupies the southwest of the Qin-Hang metallogenic belt in the connection between the Yangtze and Cathaysian plates. As one of the newly discovered large-scale Cu-Mo porphyry deposits in recent years, the Yuanzhuding deposit attracts much attention of the domestic and overseas brilliant ore experts, on which the thorough studies will contribute a lot to improve and perfect the regional metallogenic theory and to guide the future ore prospecting.After detailed dissecting of geological features to the Yuanzhuding deposit, this thesis resorts to methods of mineralogy, petrology, geochemical geology, isotopic geochronology, radioative and stable isotopic geochemistry, and inclusion studies, focus on petrogenesis, ore-forming material origin, fluid evolution, and metallogenic mechanism and geodynamic setting, and aims at establishing of metallogenic model.With the methods of field drilling data and microscope observation, the rock type that related to the Yuanzhuding ore deposit is limited to monzogranite porphyry. The ore body of the deposit is mainly in the Cambrian meta-sandstones and with a ring shape on the map, and vertically like a cylinder around the porphyry that distributed the Mo interiorly and Cu exteriorly. Due to the influence of hydrothermal fluid, alteration zoning of the deposit is very clear. For instance, the phyllic alteration zone, potassium silicated zone, phyllic-pyrite-silicate zone appear outward from inner of the porphyry and coincide well with the metallogenic zoning.Zircon U-Pb geochronology result shows that forming age of the Yuanzhuding monzogranite porphyry is153.4±1.6Ma, belonging to Mesozoic Middle-Late Jurassic. According to major and trace elements analysis results, the porphyry is enriched in LREE and HFSE and is depleted in HREE and LILE with a little Eu and Ta-Nb-Ti negative anomaly, from which the source of the porphyry is referred to garnet-bearing amphibolite and orogenic calc-alkaline series and magnetite series granite. Furthermore, zircon Hf isotope study indicates that the porphyry contains more mantle material and contaminated by continental crust during ascending and formed form a crust-mantle mixed origin. Considering forming age, rock types, geochemistry and preexist regional study data, it is inferred that the porphyry was formed under the geodynamics setting of slab window and partial-melting which is triggered by oblique subduction of paleo-Pacific plate, or Izanagi plate underneath to the Euroasian plate at Middle-Late Jurassic.The study of S and Pb isotopic geochemistry of the ore minerals show that sulfur comes mainly from the ore-forming magma and634S values of sulfide in the ore distribute in a range between-4.3‰～3.9‰. The ore-forming material source is controlled by partial-melting of subduction as well, in which the overlying sediments of the oceanic crust are the major source for the metallogenic material.Inclusion study shows that the common boiling fluid inclusion assemblage in porphyry deposit is absent in the Yuanzhuding deposit, and gaseous and liquid inclusions are the main types of the inclusions, denying the boiling and fluid immiscible formation mechanism for deposition of metal minerals in the deposit. H and O isotopes composition and fluid inclusions forming temperature and salinity analysis of quartz vein for each stage suggests that ore-forming fluid of the Yuanzhuding deposit is composed of a NaCl-H20system with medium to low level of temperature and salinity, and the magma hydrothermal fluid is the major material of metallogenic fluid with minor mixing of precipitation. That mixing betweent precipitation and hydrothermal ore-bearing magma is the key factor that caused the Yuanzhuding metallic minerals precipitated out of the ore-forming fluids.Consequently, discovery of the Yuanzhuding Cu-Mo porphyry deposit enriches the ore deposit association in the southwest of the Qin-Hang metallogenic belt. Further genesis comparison among the other porphyry-skarn Cu-Mo-Pb-Zn-Ag deposits that distributed along the same belt gives a coincident geodynamic setting, which provides a theoretical clue for prospecting the similar type of deposit in the area.