Geological Characteristics And Metallogenic Element Migration Mechanism Of Baoxinggou Gold Deposit In The Great Hinggan Mountains?NE China

The baoxinggou gold deposit is located in the southern part of the upper heilongjiang foreland basin,the northern part of the yao station fault depression and the southern part of the twenty-two station uplift.It belongs to grade IV metallogenic belt in upper heilongjiang province.Its tectonic background is the superposition of the paleo-asian metallogenic region and the Pacific metallogenic region,and it is a large rock gold deposit recently discovered.The ore bodies occur mainly in the sandstones of the twenty-two station formation of middle Jurassic or in contact with the hypabyssal dioritic porphyrite and are controlled by NE and NS trending faults.At present,more than 15 tons of resources?333+334?have been submitted,and the average grade is 1.22×10^-62.29×10^-6.Starting from the analysis of the metallogenic geological background,this paper makes an in-depth study of the geological characteristics and geochemical characteristics of the deposit,analyzes the metallogenic geological conditions.Through the analysis of the ore,quartz fluid inclusions and plagioclase by scanning electron microscopy and electron probe,combining with previous studies on stable isotopes and the metallogenic age of Baoxinggou deposit,the hydrothermal system formed,the migration of metallogenic elements and the genesis of the deposit are expected to be discussed,so as to enrich the metallogenic theory.Based on the study of regional geological background,combined with previous research results,field geological survey and indoor analysis,the main conclusions of this paper on the study of geological characteristics and metallogenic element migration mechanism of baxinggou gold deposit in the greater hinggan mountains are as follows:1.Baoxinggou gold deposit was formed in the continental extensional environment,the ore body is generally controlled by the North-East fault structure,and partly controlled by the near-east-west fault structure.The metallogenesis can be divided into four stages,and the metallogenic process may be multi-stage.2.The ore bodies were produced in veins in the contact zone between diorite porphyrite and diabase porphyrite and the sandstones of the twenty-two station formation.The metallogenic materials were mainly derived from quartz diorite and diorite porphyrite,followed by the sandstones of the twenty-two station formation.3.Gold mineralization mainly occurred in altered sandstone,altered diorite and altered diorite porphyrite.Gold mineralization is more concentrated in altered sandstone.4.Ore metal minerals are mainly pyrite,arsenopyrite,sphalerite,galena,chalcopyrite and so on.The alteration of surrounding rock is well developed,which mainly includes biotitization,adularization,albitization,silicification,sericite formation,carbonization,chloritization,anhydrition,alunitization and kaolinization.According to alteration combination and interpenetration,there are two stages of mineralization alteration in this deposit.Late mineralization is closely related to gold mineralization.The alteration of adularia-calcite indicates that the deposit is a typical low-sulfur epithermal deposit.5.The mineralization of the gold deposit occurred in 118.13¹24.92Ma and was formed in the early cretaceous.The main ore-forming fluid is meteoric water.The metallogenic heat source is derived from magmatic activity.The metallogenic temperature was between 210³20?,the salinity was 4⁹ wt%NaCl,and the metallogenic depth was less than 1.5km.6.Gold is mainly stored and transported in the form of complexes,in which Au[HS]₂^-is the most important gold complex.The mixture of magmatic hydrothermal fluid and meteoric water is the source of gold metallogenic fluid.The portability of gold is determined by its iron affinity and sulfur affinity.The early stage was characterized by high H₂O-CO₂ and low salinity migration,while the late stage was characterized by high NaCl-H₂O-CO₂ and relatively high salinity migration and accumulation.Pyrite and arsenopyrite are the main carriers of gold transport.The change of temperature and pressure,fluid boiling,fluid-surrounding rock reaction and fluid mixing are the decisive factors for gold precipitation.