Zircon U-Pb Geochronology,Geochemistry Of The Granite With Au Mineralization And Implications For Tectonic Setting In Southern Truong Son Metallogenic Belt In Laos

Truong Son metallogenic belt is distributed mainly along the border in Vietnam and Laos Truong Son granite belt in northwest trending,the north is bounded by LanJiang and the south is bounded by the DaNang-Sepon in Laos,which is developed on the basis of the fault fold zone.Paleozoic strata is exposed in the belt with multiple magmatic emplacement.The mineralization is featured by Fe-Cu-Au mineralization and is closely related to the granitic magma activity. During the Early Ordovician to early Triassic, Truong Son metallogenic belt is in the stage of metallogenic evolution with plate activity, the mineralization is controlled by the evolution of ocean-land conversion system, and mainly developing the Metallogenic system related to subduction boundary.Based on the studies of the Zircon U-Pb geochronology,geochemistry and Sr-Nd isotope system of the granite samples from the south of Truong Son metallogenic belt granite. Conclusions were drawn as follow:1.The rock samples from Truong Son metallogenic belt is per-aluminous granite, mainly belong to low potassium tholeiitic series and high K calc alkaline granite, and a few samples belong to shoshonitic granitoids.2.According to the zircon U-Pb dating and existing geochronologic data, the granitic magmatism in southern Truong Son metallogenic belt can be grouped into such three stages as (1)early Paleozoic granites(485.6Ma-461.4Ma) which related to Caledonian movement; (2) Late Paleozoic granites (401.7Ma-398.7Ma) which related to hercynian movement; (3)Late Paleozoic-Early Mesozoic granites (251.64Ma-245Ma) which related to Indo-China movement.3.Sr-Nd isotopic compositions indicate that the samples from the south of Truong Son metallogenic belt enriched mantle region. samples from LDK-23 and LDK-31 are close to the mantle zone.Combined with comprehensive analysis of REE and trace elements we can have the conclusion that the Late Permian-Early Triassic NO8 samples can be divided into two types, one is derived from mantle mafic magma, and the other is from the lower crust; LDK23 samples derived from lower crust, which is partial melting caused by mantle derived magma. LHJT sample are also derived from mantle source.4.According to the analysis of the metallogenic elements, the diorite-granites sample LDK-31 of late Paleozoic to early Mesozoic (Enrichment of elements W、Sb、Cu、As、Bi、B、 Sn、Au、Mo、Pb), as well as the quartz-diorite granite and syenites sample LZK02 of Early Paleozoic (Enrichment of elements Sb、As、W、Ag、Au、B、Sn) have a high intensity of metallogenic elements enrichment, indicating that the two types of rock mass has promising vision of the mineralization. And Consistent with the results of conclusion made before that their resourse is mantle source.5.1n the discrimination diagram of trace elements Hf-Rb-Ta, the samples are located in the island arc tectonic environment. The Late Permian to Early Triassic granites and the related deposits are in the volcanic island arc environment which generated by the subduction of Majiang ocean down to the Indosinian plate. The Early-Middle Ordovician granites and the related deposits are generated in the volcanic island arc environment by the subduction of Tam Ky-Fukuyama Ocean to the Truong Son terrane, and the Early-Middle Devonian granite are generated in extension collision environment.