Typomorphic Characteristics Of Main Gold-bearing Minerals,Gold Deposit Genesis,and Tectonic Background In The Zhesang Gold Deposit,Yunnan

The Zhesang gold deposit in Funing,Yunnan is a Carlin-type gold deposit located in the"Golden Triangle"structural belt of Yunnan,Guizhou and Guangxi.Pyrite and arsenopyrite are the best typomorphic minerals and important carrier minerals of the deposit.There is a certain regularity between the gold-bearing properties of different types of pyrite and its chemical composition and other standard characteristics.The ore in this area can be divided into diabase type,argillaceous slate or siltstone type,and marl type.The crystal form of pyrite in the three kinds of ores is mainly pentagonal dodecahedron and cube,and the gold content in descending order is fine-grained crushed pyrite,fine-grained self-shaped pyrite,coarse-grained crushed pyrite,and coarse-grained pyrite.Automorphic pyrite and colloidal pyrite.The main forms of arsenopyrite are needle columnar,columnar,and rhombus.The gold content of fine-grained arsenopyrite is better than that of coarse-grained arsenopyrite.The elemental characteristics of pyrite are Fe deficiency and S deficiency,while arsenopyrite is As deficiency and S rich.In addition,the w(Co)/w(Ni)of pyrite is between 1.731 and 3.215,with an average of 2.646(the hydrothermal origin w(Co)/w(Ni)is between 1 and 5).The crystal forms and main trace element characteristics of pyrite and arsenopyrite,indicating the origin of the middle-low temperature hydrothermal fluid in the Zhesang gold depositThrough the collection of predecessor's electron probe microscopic analysis of As and Au data of arsenic-containing pyrite in the three Carlin-like Carlin-like gold mining areas,it can be seen that Au is mainly present in the pyrite structure as a solid solution(Au~+),Only a small amount of Au participates in the structure of pyrite with nano-particle gold(Au~0).Electronic probe data analysis is carried out on the arsenopyrite and arsenopyrite of different ore types in this mining area.The positive correlation between As and Au and Au/As The ratio(mol%)is lower than the solubility limit of Au in arsenopyrite.According to previous studies,it has been shown that the gold is likely to exist in the Au complex in the form of Au~+.During the hydrothermal ore-forming period,the fluid is rich in As,and As enters the pyrite and arsenopyrite,which leads to the unbalanced replacement of As to S,causing extra cavities and/or defects on the surface of the pyrite and arsenopyrite.Arsenopyrite and arsenopyrite concentrate Au in the unsaturated ore-forming hydrothermal fluid relative to Au~0through surface cavities and/or defects and As activity,forming the Sankarin-type gold deposit.Based on the genesis of the deposit,combined with the relevant geological data of the predecessors,to understand the history of polymetallic multi-stage mineralization in the Yunnan,Guizhou and Guangxi regions and even the South China Craton,it is concluded that the main age of the mineralization of Carlin-type gold deposits in the mineralization domain is the Indosinian period.Mineralization(230-200 Ma)and Yanshanian(180-150 Ma and 130Ma)may have mineralization,but its mineralization is relatively light,mainly due to the extraction and transformation of late Indosinian mineralization.In addition,based on the Neoproterozoic tectonic thermal events in the South China Craton,a metallogenic model is established,and it is concluded that the Zhesangkalin-type gold deposit was formed in the extensional tectonic environment after the subduction of the South China Craton and Indosinian blocks.