The Geochemical Characteristics Of The Rock Mass And Their Controls Of Mineralization In Chagele Pb-Zn-Cu-Mo Deposit,Tibet

The Chagele Pb-Zn-Cu-Mo deposit is located in the western section of the Nianqing Tanggula Pb-Zn-Ag-Cu-Fe metallogenic belt and is the only large Pb-Zn-Cu-Mo deposit found in the west section of the belt,but it has no clear understandings of the geological features,the relationship between the ore-forming rock bodies,the relation of rock bodies and metallogenic types,and the metallogenic potential of the Pb-Zn polymetallic deposit on the west section.Therefore,through the systematic studies of zircon U-Pb chronology,zircon trace elements,zircon Hf isotopes,all rock main trace elements and all rock Sr-Nd-Pb isotopes of the ore-forming rocks in the Chagele deposit,we systematically discuss the relationship among the ore-forming rock bodies,among the rock bodies and the metallogenic types.At present,the following points have been made:Zircon LA-ICP-MS U-Pb dating of the monzonitic granite porphyry in the Longgen Pb-Zn ore block yielded weighted mean ages of 62.9±0.8Ma;Zircon LA-ICP-MS U-Pb dating of the granite porphyry in the north chagele Pb-Zn ore block yielded weighted mean ages of62.1±1.1Ma;Zircon LA-ICP-MS U-Pb dating of the granite porphyry in the south chagele Mo ore block yielded weighted mean ages of 63.3±0.8Ma.The magma crystallization ages of the three ore sblocks are almost identical,all of which are the products of different stages of magma evolution of the collision of India-Eurasian plate in the early palaeopalaeocene after the Yarlung Zangbo River basin to the North subduction.The ore-forming rocks in the Chagele deposit have the characteristics of high silicon,potassium rich,aluminum rich and poor phosphorus and belong to the series of peraluminous and high potassium calc alkaline rocks.The three ore-forming porphyries in the those ore blocks show the characteristics of rich lithophile elements(Rb,Th,K),poor high field intensity elements(Nb,Ta,Ti and P,etc.)and obvious negative Sr anomalies.The total amount of REE was distinct and show the distribution of"Seagull type",indicating that the rocks experienced the crystallization differentiation of different degrees.The geochemical characteristics of the rocks indicate that the ore bodies in the Chagele deposit have the characteristics of the volcanic arc co-collision granite.The characteristics of zircon trace elements indicate that the Chagele deposit is formed in the continental margin arc environment.The ore-forming rock in the Chagele deposit may be a excessive environmental product of the late subduction-early main collision.The ore-forming porphyries in those three ore blocks of the Chagale deposit have high Sr(0.709353?0.722025),low Nd(0.511763?0.512242)and the negative?_Nd(t)value(-15.48?-6.17).The Pb isotope ratios of the ore-forming rock masses in each block of the Chagele deposit are similar.The similarity of?_Hf(t)values(-8.53?-0.23)and the Hf isotope two-stage model ages(1.02?1.43Ga)of the ore-forming porphyries in each ore block of the Chagele deposit.All of above indicates that they may originate from the same magmatic source area,but own different degrees of melting of the ancient crust,and be removed from the depleted mantle from the Paleoproterozoic to the Proterozoic.However,the inhomogeneity of?_Hf(t)in each ore block is likely to indicate the interaction between the two endmembers of the mantle source with more radioactive Hf and the crust source with less radioactive Hf.Although the magmas in each ore blocks are homologous but have varying degrees of incorporation of mantle-derived materials or ancient crust materials,different stages of magma surge in place,different crystallization temperatures and magma oxygen fugacity and differentiation evolution of different rock masses,different surrounding rock conditions after magmatic emplacement,may be part of the reasons that cause the ore-forming differences in each ore block of the chagele deposit.