Discussion On The Age And Origin Of The Formation Of Mafic-ultramafic Dykes In Gold Metallogenic Belt Of Dadu River

The Dadu River gold metallogenic belt is located in the western margin of the Yangtze platform and Kangding Dadu river. The tectonic location of Ganzi Songpan orogenic belt is located in the transition zone between the north and South trending tectonic belt and the southwest Sanjiang orogenic belt. The Dadu River gold metallogenic belt of mafic-ultramafic dyke rocks are mainly diabase, the diabase dikes in the Dadu River gold metallogenic belt in typical gold deposits were found exposed. And there is a close relationship between diabase in spatial distribution. Papers to the gold mineralization in the Dadu River with mafic-ultramafic dikes of the formation of age and genesis as the focus, the geological characteristics of the deposit, geochemical characteristics, metallogenic epoch, dike chronology and previous some research results comparative analysis research of Dadu River Basin typical gold deposit in acquisition of diabase are discussed, through the study reached the following understanding:(1) the Dadu River gold metallogenic belt in the pre Sinian basement formation stage, the Sinian to Middle Triassic period, passive continental margin from the beginning to the development, the Late Triassic Cretaceous orogenic stage and Cenozoic intracontinental orogenic stage. These favorable geological tectonic movement provided favorable dynamic source, material source and migration channel for the study of the magmatic activity in the area. According to the zircon U-Pb test data, it is concluded that the Dadu River gold metallogenic belt of basic ultrabasic vein can be divided into three period, first phase for 754Ma. Such as Guza-Changheba diabase dikes; the second phase of the 430Ma, such as partial rock sub diabase dikes; the third phase of the 220mA, such as Erligou, a stick of incense diabase veins. Three basic ultrabasic rock veins with a certain distribution, namely in the basement in the dew of the mafic-ultramafic dikes exclusion platinum table and a handful of an earlier formation of mafic dikes in 220Ma formation, and in the cover layer of mafic-ultramafic dikes formed time is about 430Ma.The vast majority by 220Ma vein(2) because of the Dadu River gold metallogenic belt of the tectonic environment of complexity and multi period, contributed to the magmatic activity is more active, according to the area of basic ultrabasic rock chemical properties difference analysis can be three times the base-Ultra mafic dikes is divided into two genetic types, the first species belong to the volcanic island arc environment formation of mafic dikes and the formation period of mostly in the power source in the plate subduction and collision, material sources from the subducted slab dehydration metasomatized mantle melting due to the plate subduction fault zone upwelling form, this class of mafic dikes exist in basement strata. The second mechanism similar to MORB, intraplate rift pulls a form of, this group of mafic dikes age at about 430Ma, the material sources of the asthenospheric mantle, through the extensional environment of formation fracture Chung melt formation, the mafic dikes from dew in the cover strata.(3) the Dadu River mafic ultramafic rocks veins of rock chemical characteristics indicate that material source of the mafic ultramafic dikes from deep crust or upper mantle, the mafic dikes appear indicating the location had occurred in the deep crust or upper mantle pulling a role and the Dadu River fault is the deep crust or upper mantle deep fault. In the environment of regional tension, it is not only in favor of the deep crust or the upper mantle mafic magma intrusion, it is also conducive to the deep hydrothermal fluid migration. Similarly, previous studies show that the initial abundance of gold elements in shallow crust is very low, most of the gold in the earth's crust is derived from the deep crust or upper mantle. In field geological survey found that most of the region is gold deposit/body with mafic ultra mafic dikes in space exist close relationship, according to the project group as measured by the Dadu River gold metallogenic belt of gold deposit/age in the 5-50Ma range, far later in the area mafic ultramafic dikes formed era, so the formation of gold deposits of gold bearing hydrothermal fluids may follow the mafic ultramafic magma migration pathway.