Origin And Metallogenic Significance Of Silicalites In The Southwest Of Dabancheng, Xinjiang Uygurautonomous Region

The siliceous rocks of Qiergusitao Group of Upper Carboniferous(C2q) was widely distributed in the southwest of Dabancheng, Xinjiang Uygur Autonomous Region. The field geological mapping, commodity survey and the geichemistary characters of major elements, REE, trace elements of the siliceous rocks indicates that the genetic types of the siliceous rocks are polygene. Volcanic genesis and hydrothermal genesis are dominant, and biochemistry genesis is also contributing.The geochemical characteristics of siliceous rocks containing clast is low P₂O₅ content and SiO₂/Al₂O₃ ratio, high TiO₂ content and∑REE, and Al₂O₃/(Al₂O₃+Fe₂O₃) less than 1 which is the characters of Volcanic siliceous rocks. The siliceous rocks containing Radiolarian have the biochemical genesis characteristics of high SiO₂, P₂O₅ content and SiO₂/Al₂O₃, SiO₂/(Na₂O+K₂O) ratio, low Al₂O₃, TiO₂, FeO, MgO and alkali content, and K₂O/Na₂O, Al₂O₃/(Al₂O₃+Fe₂O₃), Si/(Si+Al+Fe) less than 1. Maroon siliceous rocks (containing iron) have the geochemical characteristics of hydrothermal sedimentary siliceous rocks which is high SiO₂, total Fe, MnO content and Fe₂O₃/FeO ratio, low Al₂O₃, TiO₂ content and SiO₂/(Na₂O+K₂O), Al₂O₃/(Al₂O₃+Fe₂O₃) ratio, K₂O/Na₂O more than 1, Fe/Ti more than 20, (Fe+Mn)/Ti near 15, lower∑REE, Ba average content 766.5ppm and Co/Ni<1. The MnO/TiO₂, Al/ ( Al+Fe+Mn ) , (La/Ce)N, Th/Sc, Th/U ratio ,δCe, chondrite-normalized REE curve and a series diagram not only can be used to indicate the genetic types of the siliceous rocks, but also show that the siliceous rocks were formed under the tectonic setting of continental margin-bathyal sea.The study area was in pullapart environment at Upper Carboniferous. On the process of the formation of the siliceous rocks of Qiergusitao Formation, proximal gravitational collapse happened and the siliceous conglomerate-diffusive lamellar siliceous rocks were formed. The sedimentary and petrological characteristics, sedimental structure, the size of grain and sedimentary sequence of the siliceous rocks were discussed in the article, and then the characteristics of the mixed provenance turbidite in the study area were discussed.