Geology, Geochemistry And Genesis Of The Saishentang Cu Deposit, Qinghai

Located in the conjugate and transfer between the west Qinling and east Kunlun orogens, Saishentang copper deposit is one of the most important medium deposits in Elashan metallogenic belt. The ore beds are low metamorphic phyllite, metamorphic siltstone and marble in lower-middle Triassic, the quartz diorite is the main metallogenic rock body. The ore body mainly produced on the edge of the rock mass and in the formation, occur as stratified, statoid and pod-like types, and have the same occurrence with its surrounding rock. The ore is divided into skarn type ore and ore of hydrothermal sedimentation, the main metallic mineral are pyrite, magnetite, pyrrhotite, sphalerite, chalcopyrite, galena, etc.With banded structure occurrences, chert contacts conformably with metamorphic siltstone. The particle size of chert is consistent with siltstone, between 50-100 um. So the chert has the characteristics of exhalative sedimentation. Characteristics of acroelements(SiO2, Al2O3, TiO2, MnO, Fe2O3, etc) show that the chert are formed at the continental margin, and affected by some terrigenous material. The REE curve normalized by NASC is horizontal, and the REE fractionation is not clear. The value of silicon isotope δ30Si for chert in Saishentang copper deposit ranges from-0.8‰to0.1‰, the average is-0.4‰, and it is overlapped with the value of hydrothermal sedimentary silicalite. The δ18O values range from 9.4‰to11.7‰, the average is 10.85‰, which consistent with the value of the igneous quartz and the quartz on the foreshore. Its because of that the formation environment is closer to the beach, so the chert affected by some terrigenous material. Also the later magmatic rock intruded the chert.A single zircon U-Pb age of 215.5±4.6 Ma was obtained from the quartz-diorite which is the product of folding orogenic movement, indicating that the suite formed in the medium-later Indo-Chinese epoch. The petrological study and studies in element and isotopic geochemistry indicate that the pluton in Saishentang belongs to calc-alkaline, high-K calc-alkaline metaluminous I-type granite, which is the product of subduction-collision process of Anyemaqen ocean, and the tectonic setting of which was volcanic island arc.Lead isotope Geochemical Characteristics of the Saishentang copper Deposit indicates that the Pb isotopic composition of skarn type ore, quartz diorite and formation constitutes a well-correlated line, reflecting that they have cogenetic relationship. While the lead isotope composition of the ore in metamorphic siltstone was dispersive. There are only some can constitutes a well-correlated line with the lead isotope composition of quartz diorite. The hot water in the mantle may provide part of the mineralizing material. This study suggested that there should be several sources of ore-forming materials and multiple mineralizations. It is thought that the deposit is the result of both hydrothermal sedimentary mineralization and medium-later Indosinian magmatic hydrothermal mineralization. A metallogenic model is established for this deposit based on above analysis results.