The Geological-geochemical Characteristics And Genesis Of Xinsheng Copper Polymetallic Deposit In Hunan Province

The Xinsheng copper polymetallic deposit is located in north of Huangshaping-Baoshan orefield and south-eastern part of the contact zone of Dayishan granite bodies. Granite is not exposed on the surface, but there are concealed bodies by drilling and tunnel engineering, which composed of biotite granite and biotite monzogranite. Wallrock alteration of mining area is strong, including greisenization, skarnization, silicification and carbonatization, which are closely related to mineralization. There are three types of mineralization:crack or fracture filled-replaced copper polymetallic mineralization, skarn-type copper polymetallic mineralization and greisen-type copper polymetallic mineralization.There are general characteristics with K-rich, Si-high of concealed bodies, which can be classified of calc-alkaline granite (the values of A/CNK are from0.93to0.98, average value is0.96; and the values of A/NK are from1.03to1.13, average value is1.08) and weakly peraluminous granite (the values of A/CNK are from1.03to1.13, average value is1.08). Concealed bodies of mining area have obvious Eu negative anomaly. REE distribution patterns show the type of "gull". This feature is same as A-type granite. The average value of10000Ga/Al is3.62(3.47-4.00), which is close to3.75, the average value of A-type granite worldwide. Discrimination diagrams for tectonic environment of granites proved that concealed bodies of mining area are A-type granites, and there are within-plate granites which formed in the post orogenic stage (A2).Zircon U-Pb dating by LA-ICPMS of concealed bodies of mining area shows that they formed in the first stage (168.5±2.8Ma) and second (147.5±3.5Ma) stage of early Yanshan movement respectively. The values of εHf(t) of zircon are all less than0, from-5.79to-4.15, indicating that there is no new growth of the earth’s crust in mining area and the magma mainly derived from a single source.The model ages of two stages ranges of zircon Hf isotope (TDM2) from1.208to1.290Ga (average value is1.227Ga). This feature indicates that granite bodies originated from melting of early crustal materials formed in mesoproterozoic. In addition, characteristics of major and trace elements illustrate mineralizing materials originated from crust and mantle.S isotope fractionation of minerals does not come to equilibrium. There is great difference of δ34S of ore samples, and their values concentrate on the two ranges (-0.65×10-3-2.03×10-3and-7.63×10-3-7.83×10-3). It indicates that S originated from non-single source:the former is characterized by mantle source; the latter imply the addition of crust materials.The study of compositions of group mineral fluid inclusions shows that ore fluid was composed of magmatic water at the early-forming stage and meteoric water at the late ore-forming stage. The temperature of petrogenesis and mineralization is from189℃to320℃, which indicates the deposit formed in middle-high temperature environment.The characteristics of full differentiation and multiple-stages activity of magma is obvious. The deposit is controlled by fracture, and the intrusion of magma which contains metal ore-forming element such as Cu, Sn, W, Mo, Pb and Zn, and volatile components F and Cl is the most significant ore-controlling factor.