The Genesis Of Volcanic Rocks Of Early Cretaceous Meiriqieco Groups And Its Relationship With Minerogenesis Of Tiegelongnan Copper(Gold) Deposit In Duolong Ore Cluster, Tibet

The exploration and breakthrough of Tiegelongnan copper(gold) deposit which is located in the Duolong ore cluster is the most important ore prospecting achievement in the Bangongco-Nujiang metallogenic belt in recent years. Determination of deposit type lays the theory and prospecting research foundation for regional prospecting. It is no doubt that it is an important guiding significance on regional prospecting and exploration that strengthening the study on metallogenic geological background of ore deposit. This paper focuses on the volcanic rock of Meiriqieco groups in Duolong ore cluster and discuses the relationship between volcano diagenesis and mineralization of Tiegelongnan deposites through investigation of field geology, petrology, isotope chronology, isotope geochemistry and other works.LA-ICP-MS U-Pb zircon geochronology research shows that the diagenetic age of Tiegelongnan andesites is(110.01±0.68) Ma(MSWD=2.3), it formed in the early Cretaceous. It is thought that the volcano eruption type is the center combination with fissure eruption through mathematical simulation of andesites’ s top and bottom interface. More detailed petrological and geochemical studies show that volcanic rocks of Meiriqiecuo groups developed a rock assemblage type of basalt-basaltic andesitesandesites and dacites, and it shows that the features of the transition from immature to mature arc and transform to the mature continental marginal arc. The geochemical characteristics shows they have the characteristics of island arc volcanic rocks and magma is from II-type enriched mantle(EM II), they are the product of subducted sedimentary melt replaced partial melting of mantle and they mixed with the upper crust during magma processing, their tectonic setting is limited to the Andean type active continental margin, this shows they are a typical continental margin island arc volcano rocks, they formed under the dynamic background of ocean crust of Bangongco-Nujiang northward subducting in the early Cretaceous and they are the magma product of this dynamic background.The petrology study on andesites enclaves shows they are pyroxene andesites that mainly occurred in the orogenic environment, the relationship between their’s location and position of the orebody in Tiegelongnan deposites is closer. The range of andesit containing inclusions can indicates the distribution of Tiegelongnan deposit,it is one of the important indicators of closing to ore body.In conclusion, the formation time of volcanic rocks is later than formation of orebody in Tiegelongnan deposites, the eruption occurred at the beginning of erosion of orebody, and then volcanite covered the orebody. This is one of the important conditions for the preservation of deposit. On the other hand, the study on volcanic rocks of Meiriqieco groups can also provides more evidence to study on metallogenic geological setting of Tiegelongnan deposit.