Geochemical Feature Of Ore-Forming Fluid In Mayoumu Gold Deposit, Tibet

Tibet lies in the huge ore-forming belt of Alps-Himalayas, which is the largest in the world and in which the background of geological structure is very useful to mineralize the gold mine. Mayoumu gold deposit is the first greater rocky gold deposit discovered in Tibet in recent years.Mayoumu gold mining area lies in the south of Mayoumu and Laangcuo-Chaiqu anticline in the mid of the area which is located in the west of Yaluzangbu River suture zone. This deposit is mainly originated from the green schist of Qiwugongba groups in Sinian system and Cambrian system. Based on the association of original mineral, ore types can be divided into gold-pyrite and electrum-sulfosalt.This text regards fluid geochemistry and theory of mineralizing as guidance, has studied the fluid source of mineralizing fluid, physical chemistry conditions of ore-forming, gold migration form and precipitating mechanism, which using fluid inclusion and the composition of hydrogen and oxygen isotope, thermodynamics research approach. The result of research shows:The ore-forming fluid of Mayoumu gold deposit may be the groundwarter hydrotherm which is formed by atmospheric water.Gold mineralization mainly takes place in mid-low temperature (198²59℃), shallow (0.85—1.14km), weakly acidic (pH=5.149⁵.347), weak reducibility (Eh =-0.104⁰.039V), low oxygen fugacity (f_O2) =10^-49.612×10⁵ —10^40.756×l0⁵Pa), rich in H₂S. Gold mainly migrates by Au(HS)^-₂, the droping of reducing sulfur concentration, pH value and temperature are the main reasons causing the gold to precipitate.The research suggests Mayoumu gold deposit belongs to the epithermal-mesothermal deposit.