Geological Features Of Diagenesis And Metallogenic Mechanism In Wandao Gold Deposit, Zhaoping Country,Guangxi

Dayaoshan region in Guangxi is well-known with producing gold which is quartz vein type gold deposits and subvolcanic rock type gold deposits in South China. Wandao gold deposit is located in the western of Gupao gold field within the Dayaoshan uplift,which is a medium-sized deposits recently discovered.Its deposit type has great controversy, some believe it is quartz vein type gold deposits, and some considers Porphyry type gold deposits.To make sure the type of deposit to guide exploration work in future, this paper focuses on studying geological characteristics of depoits, geochemical features of the granites, chronology, fluid inclusions and stable isotope etc., in order to explore mineralization periods, the evolution of ore fluids, the mineralization mechanismof the deposit etc.The study of detailed mine mapping, the measurement of profile and microscope shows that the gold ore bodies are characterized by quartz veins, which mostly presences within the granitic porphyry and Cambrian sandstone/slate. The ore bodies trend is parallel to nearly EW faults rather than around the magmatic rock in surface （ring） distribution, moreover, the ore structure demonstrate large quartz vein instead of stock work. Therefore, the Wandao gold deposit is believed to be quartz vein deposit rather than porphyry gold deposit, as same as the Gupao, Taohua gold deposit. Furthermore, great amount of Molybdenite-scheelite quartz vein are found in porphyry granite and along the contact zone of porphyry granite, cut by the gold-bearing sulfide quartz veins, suggesting the presence of two different mineralization stage.We carried out zircon LA-MC-ICP-MS U-Pb agesandRe-Osisotopedating for the ore-bearing granitic rocks in the deposit. Zircon LA-ICP-MS dating shows porphyry age of （436.1±2.1） Ma^436.4±2.4 Ma; molybdenite Re-Os chronology measurement indicating the age of tungsten-molybdenite quartz veins of （436.6±3.8） Ma. Combined with previous dating results of Taohua gold deposit（148±1OMa）, it is believed that the porphyry within the Wandao gold deposit inplaced during Caledonian, and are closely associated with tungsten/molybdenum mineralization, and gold mineralization during Yanshan.In this paper we report geochemical and petrological characteristics of the buried granite stock of the Wandao gold deposit. All samples from Wandao gold deposit in this study by rich in silica、alkali、magnesium and calcium.They are rich in K、Rb、 U、Th and depleted in Ti、Nb、Ta、P in the primitive mantle-normalized spidergrams, this confirm the truth of the formation of Granite porphyryclosely related tocontinental crustof rock,REE shows thefractionationof LREE more pronounce,but heavy rare-earth elementsis not, with a relatively strongnegative Eu anomalies indicate its source may have residual plagioclase., which shows the source of Granite porphyry may berelatedwiththe crust. The measured value of87Sr/86Sr is0.7232-0.7363,and the initial ratio of Strontium0.7146-0.7336.The measured value of143Nd/144Nd is0.5121-0.5126, and the initial value ofε Nd（t） is-6.0,-3.9,-3.6,0.1,3.7, Nd modle ages is0.93-1.95. Pb isotopeanalysis results of Granite porphyry shows the206pb/204pbrangebetween18.762and20.747,and207Pb/204Pb is15.74-15.867, and208pb/204pb is38.805-40.18. Comprehensive Sr-Nd-Pb isotopic and the geochemical of granite porphyry, this paper think granite porphyry was formed by mainly partial melting of the ancient upper crust and the latter may have a small amount of mantle material added. And this ancient upper crust may be old basement in Middle Proterozoic.Based on detailed petrographic observations, this paper carried out microthermometric and Raman microspectroscopic studies of fluid inclusions formed at different ore-forming stages in the wandao gold deposit deposit. There are three dominant types of fluid inclusions, pure vapor or pure liquid single-phase inclusions, Carbon dioxidegas phase and Liquid water two-phaseinclusions, containing Carbon dioxide three-phase inclusions.Ore-forming fluids islow salinity and CO2-rich.The hydrogen, oxygen and sulfur isotopic data imply that the ore-forming fluids in the wandao gold deposit were mainly derived from magmatic fluids, mixed with metamorphic water and atmospheric water in the process of ore-forming.The results above indicate that the fluid mixing and boiling led to the decomposition of the metal complex in ore forming fluids and ore deposition.In summary, wandao gold depoits in guangxi is quartz vein type gold deposits during yanshan, which mainly controlled by a set of EW trending faults. In this paper, we suggest that gold deposits are the most economic exploration talgets in Liucen-Taohua-Gupao gold mineralization belt, and Caledonian Shendong type quartz vein-skarn-porphyry tungsten-molybdenum deposit deserves equal efforts.