Geochemical Characteristics and Origin of Skarn Rocks in the Nuri Cu-Mo-W Deposit,Southern Tibet

The Nuri Cu-W-Mo deposit is a newly explored and proved large-scale deposit in southern Tibet.It lies in the southern margin of the eastern Gangdese volcanic-magma arc,and belongs to the southern subzone of the Gangdese Cu-Mo metallogenic belt.We chose the skarn,marble and limestone exposed in the ore district to conduct component analysis.The results show that the major elements(Ca,Ti,Al,Mg,Fe and Si)are transferring among marble,limestone and skarn rocks,and the content of the elements between these rocks exhibits a linear change.The skarn rocks are rich in LREE and deficit in HREE,and bear intense Eu negative anomalies.The marbles have the same REE distribution patterns as the skarn,so we conclude they may have some relation in petrogenesis.Based on the mineral assemblage and Eu negative anomalies in the REE distribution patterns,we infer the skarn rocks were formed in a weak oxidation,medium-high temperature environment,which is consistent with the conclusion from the study on fluid inclusions.Besides,the scarcely developed Ce anomalies in skarn rocks suggest that the fluids for skarn forming were mainly derived from magma,and mixed with a lot of meteoric water.Combined with the geochemical characteristics of different rocks,intense differentiation of LREE and HREE,Eu negative anomalies,and the fact that skarn rocks are different from the hydrothermal exhalative mineralization system,we infer that the Nuri deposit was formed by fluid metasomatism.