Geological And Geochemical Characteristics And Metallogenic Prospect Of Baiyun Gold Deposit,Liaoning Province

Baiyun gold deposit is a large gold deposit in east Liaoning,and after years of exploration and mining,it has accumulated the rich information and valuable experience since was found in 1978.On geotectonics,Baiyun gold deposit is on the Sino-Korean Paraplatform,in the middle part of Liaodong rift and in the intersection of Yingkou-Kuandian palaeouplift and Dashiqiao-Caohekou fault sag.It experienced a long geological process and very deep metamorphism,which presents structural development and frequent magmatic activity.The ore bodies are hosted in the liaohe group mesometamophic rocks,the ores are belonged to easy separation type with simple composition,which is of a fine prospecting prospect.Different geologists have been arguing about the origin of ore-forming materials and the deposit genesis.Hence,the systematic study on geological and geochemical characteristics of Baiyun gold deposite including determining the origin of ore-forming materials and minerogenetic age can provide abundant data for the further research,which is of great practical significance for further prospecting of Baiyun gold deposits,and also provides new ideas for research on the genesis of gold deposit in Liaodong area.At first,the regional geological background and geological characteristics of Baiyun gold deposit are summarized.Then with systematically study on the geochemical characteristics of Liaohe group and dikes as well as stable isotope,minerogenetic age of the deposit.The genesis of the deposit has been discussed.This master's thesis achieves the following main results and understanding:(1)The ore bodies of Baiyun gold deposit are mainly consist in the EW fault zone in the middle of the mining area,which is subjected to early ductile deformation with a superposition of brittle fracture at the ore-forming stage.Ore bodies often appear in horizontal and vertical directions for the characteristics of thinning out and reappearing and branching and compounding.(2)The main types of alteration of the surrounding rock are : potassic feldspathization,silicification,calcitization,pyritization,sericitization and chloritization.Potassic feldspathization mainly include microclinization,with metasomatism of abundant aluminium mineral: sillimanite and plagioclase.The siliconization is extensive and is closely related to the mineralization.In space,potassic feldspathization is relatively developed in the deep with silicification in the shallow.Gold Ores tend to be enriched in where potassic feldspathization decreased and silicification increased.(3)The research of ore-forming elements abundance show that the mineralization elements such as Au,Ag,Cu,Pb and Zn in the Liaohe Group have not been significantly enriched and have not reached the enrichment degree of the "source layer".There is a significant difference between the element association and the ratio of elements of Liaohe Group and the mineral.It is concluded that the metallogenic material of Baiyun gold deposit is not directly related to the Liaohe Group.(4)Based on the study of the stable isotopes of H-O-S-Pb-C,it is believed that the ore-forming fluid of the deposit was mainly composed of magmatic fluids.The source of ore-forming material is closely related to the widely exposed veins in the region,and they are the same tectonic-magmatic activity as the ore-bearing fluids.In space,almost all of the upper and lower plates of the main orebodies have the distribution of the diorite porphyrite,quartz porphyry and so on.(5)This paper has carried out LA-MC-ICP-MS zircon U-Pb dating.The ages of diorite porphyry and granite porphyry are dated at(228.96 ± 0.97)Ma and(230.45 ± 0.81)Ma,respectively,combined with the ages determined as 196~ 197 Ma,207~ 209 Ma respectively for the two quartz samples separated from gold-bearing quartz-feldspar alteration rock in Baiyun gold deposit,It is believed that the mineralization age is Indosinian epoch.(6)The Baiyun gold deposit is formed under the extensional system after the orogeny,and is a magmatic hydrothermal gold deposit related to deep magmatic-fluid activity.According to the ore controlling factors,the alteration of the surrounding rock and the division of the elements,it is believed that the Baiyun mining area still has a great prospecting prospect,especially deep.