Genetic Mineralogy And Depth Prospecting Prediction Of Yi Xingzhai Quartz Vein Type Gold Deposit In Fan Shi County, Shan Xi Province

Yi Xingzhai gold deposit, the large-scale quartz vein type gold doposit in the Northeast of Shan Xi province, lies in the northern part of intermediate zone of North China Craton. The proved reserves of the deposit is closed to exhausted. The regularity of the ore genesis and mineralization enrichment is studied by genetic mineralogy research of quartz and pyrite in this thesis. Base on the understanding, the prospective prognosis in depth and periphery of the auriferous quartz vein ore were proposed.It has 9 gold-bearing quartz veins exploited for the moment in this orefield. The overall trend of the gold-bearing is NW and NNW, and the attitude is nearly vertical. The wall rock is biotite-amphibole-plagioclase-gneiss; There is Yanshanian- Sunzhuang mixed Diorite in the area south-east of the mining. Alteration type characterized by broad K-feldspar-red rock developed. Silication and beresitization distributed in the deposit near the range of 2¹0m. Mineralization phase contain beresitization phase, pyrite-quartz phase, quartz-pyrite phase, quartz- polymetallic-sulfide phase, and quartz-carbonate phase.Sulfate minerals such as tennantite and matildite are widely developed in lode gold deposit based on the results of electron probe analysis. The major mineral containing gold is electrum, and it can exist in sulfide minerals and quartzes as inclusion, intergranular minerals and fissure minerals. From 1350m level to 1070m level in stope, the fineness of electrum decrease from 768.48‰to 641.76‰, showing reverse zonation with increasing depth.The typomorphic characteristics of pyrite: the chemical composition shows that pyrites are rich in Fe; The N type is the domestic thermoelectricity type, and the absolute value of the thermal electricity coefficient display regular high-low-high style changes. The decrepitation temperature of pyrites ranges 146～343℃; Unit cell parameters are generally high; trace elements data presents that Pb and Zn concentrate in the upper part of ore body; Co/Ni content rate indicates the deposit has magmatic hydrothermal deposit characteristics. The data combining with REE and HFSE information indicates that the hydrothermal ore-forming solution is Cl-rich fluid.The typomorphic characteristics of quartz: gold-rich quartz display bimodality model luminescent curve characterized with double peak shoulders changing from high-low style to low-high style from left to right and half height width increasing. Fluid inclusions mainly consist of 2 types, fluid-rich type and V-L type with significant composition of CO₂,H₂O,Na⁺,Cl^-,SO₄^2-. The study shows that or-forming fluid is middle-low temperature, middle salinity fluid belonging to weak acid and reducing environment.The result of stable isotope show that the ore-forming hydrothermal fluid of the deposit is magmatic fluid at early stage and incorporated some meteoric water in late. The matallogenic material come from the border between the upper mantle and low crust. Considering the characteristics of ore forming fluid, it is attributed to hypabyssal-medium-low temperature–magmatic hydrothermal deposit. Based on the contour map of gold grade, the changes of ore body occurence, the typomorphic characteristics of typical minerals, and the contact relationships between different geological bodies in field, thirteen predicting target areas (three of them were in the first list) were proposed in depth and peripheral.Among the first list, there are 2 targets have been verified by drilling hole in field.