Geochemistry and Diagenetic Pattern of Ore-Bearing Rocks about Two Types of Gold Deposit in Fengxian-Taibai Basin, South Qinling

Baguamiao and Shuangwang gold deposit are two important gold types in Fengxian-Taibai basin. The gold deposits are all located at the bottom of the Upper-Devonian Xing-hongpu Formation. However the ore-bearing rocks are different between them. The ore-bearing rock of Baguamiao gold deposit is ankerite rocks, which is concordant with the strata by bedded or stratoid and assume rhythmic layering form. The ore-bearing rock of Shuangwang gold deposit is albite breccias, which are mostly lens-shaped. The data of petrochemistry show that both of them are poor in Fe2O3 and K2O, which are different from normal sedimentary rocks. The elements contents of Cu, Pb and Zn are close to Clarke value. But the content of dispersed element Ge is rich in rocks, which reflect hydrothermal sedimentary origin. The characteristic of REE are different between them. The REE contents of ankerite rocks are low and elements of Ce and Eu are positive anomaly. The REE contents of albite breccias are close to regional strata and elements of Ce and Eu are middle negative. The chondrite-normalized REE patterns are also alike. It’s shown that the diagenetic fluid are high-density which been mixed by sea water slightly. So the ankerite rocks hold the REE characteristic of thermal fluid. The diagenetic fluid of albite breccias are low-density thermal fluid which been mixed by sea water intensively. It has same REE characteristic to normal sedimentary rocks.