Magmatism And Scheelite Mineralization In The Qinhai Tongde Jiawu Mine Area

The Jiawu mine area is located in the contact area of the Qinling orogene and the East Kunlun orogene,also known as the Qinhai Nanshan micro orogene.Base on study of petrography,whole rock geochemistry,mineralogy,fluid geochemistry research,combined with previous data,we discuss about magmatism and genesis of metallic mineral origin,the regional dynamic,thermodynamic characteristics and scheelite mineralization.The study has important significance for guiding the geological prospecting.The granites in the Jiawu mine area are I type granite.Granodiorite has the characteristics of high sodium,low potassium,peraluminous,and belongs to high-K calc-alkaline granties.The rock is enriched in large ion lithophile elements(LILE)such as Rb,Ba,U,Th,lowly depleted in high field strength elements(HFSE)such as Ni,Ta,Ti.REE has a significant fractionation.The anomalies of europium and cerium are not obvious,while strontium is slightly negative.Granite-porphyry has the characteristics of high sodium,low potassium,peraluminous,and belongs to calc-alkaline granties.The rock is enriched in large ion lithophile elements(LILE)such as Rb,Ba,depleted in high field strength elements(HFSE)such as Ni,Ta,Ti,strong fractionation between light and heavy rare earth elements.The value of Yand Sr is low,at the same time,it has a weak Eu negative anomaly.Combined with regional dynamics study and diagenetic age analysis,the granite porphyry originated from the old crust and granodiorite originated from the lithospheric mantle.The main fluid inclusion type of Quartz veins with different output states in the Jiawu mine area is the rich liquid inclusions.The temperature of ore-forming fluid is between 200~ 290?,and the salinity is lower than 10 wt% Na Cl.These show ore-forming fluid has the characteristics of epithermal.Hydrogen and oxygen isotopic datas show that the ore-forming fluid is probably derived from magmatic fluid,and does not exclude the possibility of mixing a small amount of metamorphic fluids.Electron probe analysis show that compared withtheoretical value,the main Scheeliteconstituent has the characteristics of low W,slightly high Ca,and the value of Mo is lower than 0.1%.With different types of scheelite composition were compared,the Jiawuscheelite showed characteristics of quartz vein type tungsten scheelite.At the same time,analysis on relationship between WO3-Ca O and scheelite cationic W-Mo-Ca triangular diagram,also showed the same type.In summary,ore-forming fluid of the Jiawu scheelite deposite has the characteristics of epithermal,its origin is closely related to granite in this area.The Jiawu scheelite deposite is the quartz vein type scheelite deposit.