Two Types Of Copper Mineralization In Tongyugou,East Kunlun

The Tongyugou copper deposit,located in the conjunction between the East Kunlun and West Qinlin orogens,is one of the most important copper deposits in the Ela mountain metallogenic belt.The ore-forming process of this deposit can be divided into hydrothermal-sedimentary mineralization period and magmatic-hydrothermal mineralization period,of which the latter is the main mineralization period.The hydrothermal-sedimentary mineralization period is characterized by the occurrence of microcrystalline quartz,chalcopyrite and pyrrhotite.The silicalite in Tongyugou is mainly hosted within the lower-middle Triassic rocks with bedding and banded structure.It mainly consists of micro-fine crystalline quartz grain with minor sericite,chalcopyrite and pyrrhotine.And no biological related texture has been observed.The Al₂O₃-Ti O₂,Fe-Mn-(Cu+Ni+Co)×10 and P₂O₅-Y diagrams and Si-O isotopic characteristics suggest that the silicalite was formed through hydrothermal sedimentary process.And the Si/Al and U/Th values and rare earth element geochemical characteristics also suggest that the hydrothermal sedimentary system had been contaminated by some continental materials.Furthermore,the Al₂O₃/(Al₂O₃+Fe₂O₃)-Fe₂O₃/Ti O₂,Ti/V-V/Y and(La/Ce)N-Al₂O₃/(Al₂O₃+Fe₂O₃)diagrams as well as rare earth elements characteristics suggest a continental-margin environment for the formation of silicalite.The minerals formed during the magmatic-hydrothermal mineralization period are mainly garnet,clinopyroxene,amphibole,chlorite,coarse quartz,chalcopyrite and pyrrhotite,of which chalcopyrite and pyrrhotite show close relationships with skarn in the form of filling in the space between garnet and diopside.The garnet in Tongyugou yields a Sm-Nd isochron age of 216.3+1.9 Ma(MSWD=2.9),suggesting a Late Triassic time for the magmatic hydrothermal mineralization.Eight ore samples closely related to the skarn show similar lead isotopic compositions with the Saishitang intrusion rocks,suggesting that the ore-forming materials during the magmatic-hydrothermal mineralization period were mainly derived from Saishitang intrusion rocks.With the northward subduction of the Anyemaqen Ocean in early-middle Triassic,the Tongyugou area became a back-arc basin where exhalative sedimentation occurred and produced the initial source bed for ore-forming minerals.And the silicalite was an important recorder of the mineralization event.During the late Triassic East Kunlun collisional orogeny,the intrusion of Saishitang granitic magma produced magmatic-hydrothermal fluids which led to the reactivation and concentration of ore-farming materials in the initial source bed and the metasomatism of the carbonate formations,which led to the large-scale skarnization and copper mineralization and the formation of the Tongyugou copper deposit.