The Characteristics Of Ore-forming Fluid And Genesis Of The Matou Mo Deposit,Chizhou,Anhui

The Matou Mo deposit is located in the Anqing-Guichi ore cluster area of the middle and lower Yangtze metallogenic belt.The ore bodies are mainly hosted in granodiorite porphyry.According to the types of ore bodies and alteration,the ore bodies are divided into shallow quartz vein type orebodies and deep vein disseminated orebodies.The alteration types in shallow parts mainly include silicification,minor potassic feldspathization,sericitization,argillation and carbonatation.The deep parts are mainly composed of strong potassic feldspathization and silicification.The ore minerals in the Matou Mo deposit are mainly molybdenite,chalcopyrite and pyrite,with a small amount of magnetite,pyrrhotite,sphalerite,and galena.Gangue minerals are mainly K-feldspar,quartz,sericite,calcite.The fluid inclusions in shallow quartz vein type ore bodies and deep vein disseminated orebodies are studied.Through microscopic observation,three main types of inclusions are identified:two-phase aqueous solution inclusions(type ?),two-phase CO2 rich inclusions(Type ?)and three-phase CO2 rich inclusions(Type?).The shallow quartz veins are mainly type ? inclusions,while deep orebodies contain type ?,? and ? inclusions.Study of fluid inclusions showed that type ?inclusions in the shallow quartz vein homogenized into liquid phase,with homogenization temperature 224 to 283 ?.The salinities are between 3.8 and 7.6 wt.%NaCl equiv..Type ? inclusions in deep veinlet disseminated orebody homogenized into liquid phase with homogenization temperature 257 to 306 ?,and the salinities are between 5.1 and 10.3 wt.%NaCl equiv..Type ? inclusions homogenized into gas phase,and homogenization temperature is 365 to 381 ?,with the salinities rang from 0.5 to 2.0 wt.%NaCl equiv..Type ? inclusions homogenized into liquid phase with temperature 331 to 370 ?,and salinities range from 2.7 to 6.7 wt.%NaCl equiv..The study of fluid inclusion shows that the ore-forming fluid of shallow quartz vein orebody is NaCl-H2O system,while the ore-forming fluid of deep vein disseminated ore body belongs to NaCl-H2O-CO2 system.A large number of type ?and type ?,type ? inclusions coexist in the same quartz in the deep quartz veinlet disseminated ore,and they have similar homogenization temperatures and instead uniform way,indicating that the fluid immiscibility may be occurred in mineralization of the deep veinlet disseminated orebody.Immiscibility affects the chemical properties of fluids,thus causing the molybdenum complex in the ore-forming fluid to decompose and precipitate to form molybdenite.Type ? and ? Fluid inclusions from the deep vein disseminated orebodies were used to calculated stress.The stress of mineralization was 65-90 Mpa,corresponding metallogenic depth 2.4-3.3 km.Alteration mineralogy research shows that the deep veinlet disseminated orebody exerts typical porphyry deposit alteration characteristic,with potassic alteration,silicified zone and minor sericite zone.Fluid inclusion research show that the porphyry deposit metal concentration mechanism not only including the classic porphyry deposits in South America the extensive development of NaCl-H2O±CO2 system fluid boiling,also includes the NaCl-H2O-CO2 system fluid immiscibility.The identification of immiscibility for the NaCl-H2O-CO2 provides an evidence for the porphyry genesis of Matou molybdenum deposits.