Study On The Geological Characteristics And Genesis Of Shajingou Gold Deposit,Yanbian Area,Jilin Province

The Shajingou gold deposit is located in the northern margin of the North China Craton and adjacent to the Xingmeng Orogenic Belt.The structures of the mining area mainly consist of two groups of NE-trending and NW-trending fault structures.The NE-trending faults are mainly regional deep faults,and the NW-trending faults are the main ore-controlling structures in the mining area.The intrusive rocks in the mining area mainly develop Indosinian granites,Yanshanian diorite and intermediate-basic dikes.The hosted rocks of the gold deposit are diorite and intermediate-basic dikes,which of the latter are closely related spatially auriferrous quartz veins.The ore-forming process of Shajingou gold deposit is mainly divided into four mineralization stages,magnetite-quartz-orthoclase stage?stage??,quartz-pyrite-pyrrhotite stage?stage??,polymetallic Sulfide stage?stage??and quartz-carbonate stage?stage??,in which stage?and?are the main metallogenic stage.The types of ore-forming fluid inclusions are complex,mainly composed of aqueous and gas two-phase,daughter mineral-bearing three-phaseand CO₂-rich three-phase inclusions.The stage I fluid inclusions are daughter mineral-bearing three-phase inclusions with456-478?homogeneous temperature and 51.70%-53.81%_NaCleqv salinity.The stage II fluid inclusions are coexisting with CO₂-rich three-phase and gas-aqueous two-phase inclusions with 297-365?homogeneous temperature and 0.62wt%-10.37wt%_NaCleqvaCleqv salinity,indicating Fluid-boiling or immiscibility.The stage?fluid inclusions aregas-aqueous two-phase inclusions with homogeneous temperature of 238-279?and salinity of 1.56wt%-10.11wt%_NaCleqv.The stage VI inclusions are gas-liquid two-phase inclusions with homogeneous temperature of 224?±,salinity of 1.9 wt%-8.27wt%_NaCleqv.By analyzing ore mineral combination and fluid characteristics,It is suggested that the fluid system is oxidizing in stage?,and is neutral and reductive in the main ore-forming stage?stages?and??,while is weakly alkaline and weakly oxidizing in stage?.The ore-forming depths of the Shajingou gold deposit are estimated to be 9.5-9.7km,6.9-9.2km,6.0-7.1km and 5.9-6.3km respectively in the stage?,?,?and?.The H-O isotopic composition of the Ore-bearing quartz shows that the?D is-79.9‰to-97.9‰,and the?¹⁸O_H2O is 0.8‰to 6.9‰.Mainly through H-O isotopic data and fluid characteristics analysis,it is suggested that the fluid is mainly composed of magmatic water,and atmospheric water is added in the later stage,and stage?fluid-boiling and stage?fluid mixing between atmospheric water and magmatic water are the key facter in Au precipitation.The?³⁴S_V-CDT value from the ore metal sulfide is-2.4‰to+1.0‰,within the range of Meteorites?³⁴S_V-CDT value,which indicates that the sulfur source is a deep source?magmatic or mantle source?.Finally,it is determined that the metallogenesis of the Shajingou gold deposit is mesothermal-?hypothermal?vein-type gold deposit.Here,the paper also present a detailed study on the U-Pb dating,magma source,and tectonic setting of the diorite-porphyrite dykes associated with mineralization.The zircon U-Pb dating of the dykes yields an early Cretaceous age of 133.4±1.4 Ma.The rocks are alkali-calcic and aluminous to weak peraluminous,and have lower Rb/Sr?0.04⁰.11?,higher Nb/Ta?13.47¹7.02?,which are indicative of mainly mantle-derived magmas.These indicate that the magmas that formed the dykes were generated by melting of upper mantle material.Higher Na contents of the samples indicate that the magma source is could be derived from an depleted mantle source.They are enriched in LILEs(e.g.,Rb,Ba,K,Sr,LREEs and lively incompatible elements?e.g.,U?,but are depleted in HFSEs?e.g.,Ta,Nb,Ti?,showing characteristics of volcanic arc magmas.This characteristics can be identified on the La/Yb-Sc/Ni and La-P₂O₅ tectonic setting discrimination diagrams.For the northeastern China,the Early Cretaceous to Early Late Cretaceous entered the second peak of the palaeo-pacific plate subduction in the early stage and was consistent with the peak period of lithospheric thinning in eastern China.Along with the continued subduction,a series of hydrothermal deposits were formed under the extension system from the northeastern China,The different types of hydrothermal deposits in the region are formed under a unified tectonic setting,and constitute hydrothermal deposit minerogenic series at the different crust depth levels.such as the widely-developed epithermal gold deposits in the eastern part of Jilin?such as Naozhi,Jiusangou,Dong‘an,Jinchang,Sipingshan and Sandaowanzi gold deposits,etc.?;mesothermal gold deposits?such as Shajingou,Xicha,Nancha,and Jinchanggou gold deposits,etc.?and porphyry copper deposits?such as Changfagou and Tianhexing Copper deposits,etc.?.