Geochemistry Trace Of Subsurface Geology And Mineralization For Yangjiaba Polymetal Field Of South Qinling

Qinlin orogene is one of the important metallogenetic belt for China.The Mian(Mianxian)-Lue(Lueyang)-Ning(Ningqiang) triangle block lying in the south Qinlin collision belt of Yangtz plate and Huabei plate is composed of Mian-Lue tectonic belt and Bikou micro-block and northwest Yangtz plate.It is a important ore serried area, where occur many middle-large deposits of Au,Ag,Cu,Pb,Zn,Ni and so on. According to the regionally geological background datum,the Mian-Lue-Ning block has undergone processes with rifting and accretion of paleo-basement during late Archaean to early-mid Proterozoic, piece togather in late Proterozoic, lifting togather during Caledonian and Indosinian-Yanshanian orogenics, and it has characteristics of alert crust-mantle impact, complicated tectonic movememt, substance-energy exchanging frequently,and mineralization notability. The subsurface geology play a important role in mineralization with the special geological background. We choose the Yangjiaba polymetallic ore field as object of study to research it's subsurface geology process and mineralization through study of fluid inclusion,rare-earth element,trace element and isotopic element from rock and ore in Mian-Lue-Ning triangle block.The divided-area phenomenon(A and B) for the distribution of fluid inclusions types is discovered by analyzing and studying for series characters of fluid inclusions in minerals from quartz veins which were closest to mineralization in the polymetallic ore field. Pure liquid-inclusion distributes mainly in area-A and homogeneous temperature of primary gas-liquid-inclusion, which is composed by H₂O, 184℃. Primary gas-liquid-inclusion (big volume and high gas space ratio), composed by H₂O and C₆H₆ ,distributed mainly in area-B and its homogeneous temperature has higher temperature than the highest temperature(293℃) that was tested by other researchers, was 245-348℃, concentrating to 260℃and 330℃. The result shows that ore-fluid of higher temperature and reducibility was concerned with mineralization in the polymetallic ore field.The characteristics, as rich in LREE and different assembled abnormity of Ce and Eu and Yb, are found in ore and quartz-calcite veins and volcan host rock by analying and studying their REE and trace element. It is concluded that the rich in LREE is one of the obvious characeristics for the action of mantle fluid. Anomalies of positive Eu and negative Ce and Yb in ore and veins and the H2O-C6H6 fluid from fluid inclusion in vein are the important symbols that the mantle fluid has the nature of high temperature and reluction. Existence of anomalies of positive Ce and negative Eu and Ce,Eu,Yb nanomlies'weakening and disappearance are an expresssion as mixing of crust-mantle fluid and matter. Pattern of trace elements of Veins ,mineralized rock and ore are similar. Comprehensive research indicates that poly-metallization is controled by the mantle fluid being of the natures of high temperature and reduction and rich in LREE. It is the strong mixing of crust-mantle fluid and matter to play an important role in the poly-metallization, but the mante fluid is of domintant position in the process from start to finish..Research detectes that previous"dolomite"displayed the occurrence of intrusive contact in volcanite series for mid-Proterozoic Bikou Group, and the rock is confirmed as carbonatite which derived from mantle based on the studies of petrography, geochemistry of elements and isotopes. The carbonatite had an ensemble displays in the aspects of enriching LREE and LILE (large-ion lithophile elements), especially Sr and Ba, and depleting transition elements, especially Ti, Cr and Ni. Else as HFSE (high field strength elements) had more enrichment in metallizing alteration carbonatite than in weak or no alteration rocks. The understand is compatible with petrographic features, which polymetallization was accompanied by silication and sulfide alteration, and isotopic study results that setting was similar as EMâ…¡enriched mantle and the rock had intergrade from carbonatite to carbonate rock. The research conclusions suggested that the metallization related to the formation of carbonatite were probably correlate intimately to crust-mantle superimposed alter, which was resulted in syngentic mineralization or intensive land orogenesis while the tectonic framework was transformed from mid-Proterozoic to Meso-Cenozoic for Qinling orogene. Therefore, discovery and confirmation of carbonatite provide new petrology evidence for study subsurface geo-geochemistry geology dynamic event and process, and contribution that crust-mantle contamination superimposed alter improved metallization.Syngenetic mineralization of Proterozoic is one of the reasons that Qinlin orogene is one of the important metallogenetic belt, however, a more important reason for this is the mineralization based on crust-mantle contamination superimposed alter after syngenetic mineralization. The geologic background of superimposed mineralization has close relationship with transformation of Qinlin orogene's tectonic framework in Meso-cenozoic.So, from this perspective, by the deep fluid being of the natures of high temperature and reduction and rich in LREE and carbonatite magma upsurge to crust in this backdrop of subsurface tectonic dynamics ,then mixed with substance and fluid of crust to different extent together with mineralization.Though there is not the exact age data of fluidic activity,the action of mantle fluid in this reaserch, either shows that the special process of subsurface geology lay the substance foundation for syngenetic mineralization of Proterozoic together with volcanic action of Bikou group in mid- Proterozoic at that time or become a sign of the significant event during the process of extensively alter mineralization of Qinlin orogene.