Deqin County Lu Spring Copper-polymetallic Deposit Geological And Geochemical Characteristics And Genesis Of Study

The geological and geochemical characteristics of the Luchun copper-polymetallic deposit are discussed in the paper based on the basic geological data and a large amount of collected geological and geochemical data through the well-knit field and indoor work of the and the team researching the subject.Several problems of great importance to deposit research,including the source for metallogenic substance, metallogenic environment and the original pattern of deposit are primarily explored.Jinshajiang Paleo-Tethyan Orogenic belt is an important metallogenic belt of china. Luchun copper-polymetallic deposit is just located in the taking-up position of this belt. Jinshajiang Orogenic belt is formed by Palea-Tethys Jinshajiang ocean crust and arc rushing westward to subduction and collision. This composite orogenic belt collided and jointed by intra-oceanic arc and continental margin colcanic arc in early or middle Trissic period. To the East the belt is abutted with Zhongza-shangri-la micro-landmass and to the west it is adjacent to Changdu-Lanping-Simao micro-landmass. The belt was evolved by the breaking up during Devonian and Carboniferous, expanding and formation of oceanic basin during Late Carboniferous and Early Permian, westward subduction of Jinshajiang ocean crust, during Permian, extending at back-arc in times of Early Triassic and arc land colliding in the Late Triassic. Luchun-Hongpo back-arc rift basin is located in the middle section of Jiangda-Deqin-Weixi volcanic arc, and formed in the back-arc extension environment after the subduction of Jinshajiang ocean and is a strip-like sedimentary basin with a nearly N-S directed alignment.Revers of strata occurred through the area since the growth of large-scale over-thrust and nappe-extensional detachment structure. The strata in chronological order are Early Triassic Pantiange Formation (Tip), Cuiyibi Formation(T1c), Middle Triassic Shanlan Formation (T2S) and Hongpo Formation (T3h) from top to bottom. The strike direction of the strata are overall N-S and east-dipping. The geochemical characteristics of major elements, trace elements, and rare earth elements of Chlorite rocks, cherts and landed limestones show that their formations are closely related to the bimodal volcanic activities. Chlorite derived from rhyolitic volcanic tuff, laminated cherts and banded limestones are hydrothermal sedimentary rocks related to deposition of submarine exhalative hydrothermal (hot water).The research result of the zircon U-Pb geochronology shows that the volcanic rocks is a combination of bimodal volcanic rock developing in the Early Triassic. Typically the basalts are composed of tholeiite and calc-alkaline series, the rhyolites are mainly composed of calc-alkaline series, which are the main ore-hosting rocks. Geological and geochemical characteristics of the mineral area that indicate the bimodal volcanic rocks are the product of back-arc expanding environment formed by Jinshajiang ocean crust colliding with Changdu-Lanping block.The evidence from ore-forming elements and REE indicates that the ore-forming material of the deposit derived from the underlying bimodal volcanic rocks, especially the felsic rocks by the means of the hydrothermal leaching.The result shows that Luchun copper-polymetallic deposit is a the Zn-Pb-Cu polymatallic type of volcanogenic massive sulfide (VMS) depositformed in bimodal-felsic rocks under the environment of initial arc.