Early Paleozoic Magmatism And Metallogenesis In Dayaoshan Area,Guangxi Province

The Dayaoshan area,in the southwestern Qin-Hang belt,is located in the joint area of Yangtz plate and Cathaysia plate,which was historically famous for quartz vein type gold deposits.Recently,a series of Early Paleozoic granitoids related porphyry-skarn-quartz vein type W-Mo polymetallic deposits were found in the Dayaoshan area,which show well exploration prospects.As these deposits were lately found,their magmatism and metallogenesis are not well studied.To solve this problem,the newly founded Yupo tungsten polymetallic deposit in the Dayaoshan area was selected as an example for this study.Hopefully,this study will improve our understanding of Early Paleozoic magmatism and metallogenesis in the South China.Yupo tungsten polymetallic deposit is an Early Paleozoic granodiorite related skarn type deposit.We firstly obtained the SHRIMP zircon U-Pb age?441.9±1.9Ma?of Yupo granodiorite and molybdenite Re-Os age?437.9±2.9Ma?.Combined with previous data,we proposed that there is a significant Early Paleozoic granitoids related W-Mo polymetallic metallogenic event with ages range 470Ma to 420Ma in the Dayaoshan area,even in the South China.Geochemical data show Yupo granodiorite is weakly fractionated I type granite?Rb/Sr=0.33¹.24;A/CNK=1.03¹.18?,which is dramatically different with general opinion that the tungsten deposits are closely related to highly fractionated granitoids,indicating some tungsten deposits have no strict preference for the degree of differentiation of magma,which means W deposits can form from either highly or weakly fractionated granitic magma.Results of oxygen fugacity show the Yupo granodiorite is relatively reduced?FMQ–0.57?,which is beneficial to the precipitation of tungsten element.Elevated zircon?¹⁸O_V-SMOW values?5.9 to 7.2‰?and negative?Hf?t?values?–3.2 to–0.8?,together with T_DM2 of 1.5 to 1.6 Ga indicate that these plutons formed via partial melting of a Mesoproterozoic crust mixing with some mantle materials.Studies of fluid inclusions and H-O-S isotopes show the ore-forming fluids came from magmatic water with injection of meteoric water in the late stage,and ore-forming elements?eg.W,S?came from the magma.Temperature drops,pH rises and fluid mixing are the primary mechanisms of ore-forming materials precipition.Trace elements in the sulfides are mainly exist in the mineral lattice in the form of isomorphism.Analyses of ore-controlling factors show the ore bodies are mainly distributed in the inside and internal or external contact zone of plutons.Hereby,we firstly built the deposit model of the Early Paleozoic porphyry-skarn-quartz vein W-Mo deposits in the Dayaoshan area.As the absent of Early Paleozoic depleted mantle,i.e.new oceanic crust,we proposed the Early Paleozoic orogen is an intracontinental orogen.