Discussion On The Characteristics Of Ore-forming Fluids And Genesis Of Hadamengou Gold Deposit In Inner Mongolia

The Hadamengou gold deposit is located in the Wulashan Daqingshan gold concentration area on the northern margin of North China platform,which is the largest gold deposit in Inner Mongolia.The deposit has a history of more than 30 years since its discovery.A lot of geological exploration and scientific research work have been carried out on Hadamengou gold deposit by predecessors,but there are still great disputes on the characteristics of ore-forming fluid and the genesis of the deposit.In this paper,the characteristics of magmatic rocks,fluid inclusions,diagenetic chronology,metallogenic materials and fluid sources of Hadamengou gold deposit are studied systematically by means of the methods and means of rock geochemistry,isotopic geochronology,stable isotope geochemistry and micro-temperature measurement of fluid inclusions,and the genesis of the deposit is preliminarily discussed.The following main conclusions are obtained:(1)The Hadamengou gold deposit is obviously controlled by the EW-trending structure.The orebody can be divided into three types : quartz vein type,K-feldspar-quartz vein type and potassium-silication altered rock type.The main ore mineral is pyrite with the total sulfide content is not more than 5 %,which is a poor sulfide orebody.(2)The Dahuabei intrusion and Shadegai intrusion are I-type granites with high potassium calc-alkaline series and quasi-aluminate-weak peraluminate.The REE characteristics of some samples in the central phase of Dahuabei intrusion and the pegmatite veins developed inside the intrusion are similar to those of the orebody,both of which are right dipping type and have obvious positive Eu anomaly.(3)The geochronology study shows that the emplacement time of Dahuabei intrusion(360? 350Ma)and Shadegay intrusion(235 ? 220Ma)are similar to the occurrence time of gold mineralization in the area,and the nearest distance between the orebody and the above intrusion is not more than 5 km,indicating that the Dahuabei intrusion and Shadegai intrusion may have a certain genetic relationship with the formation of gold deposits.(4)The study of fluid inclusions shows that the types of fluid inclusions,the variation trend of homogenization temperature and salinity,the fluid system and the gas-liquid phase components in the inclusions in Dahuabei intrusion and orebody have similar characteristics,indicating that the rock-forming and ore-forming fluids in Dahuabei rock intrusion and orebody have certain similarities.(5)Isotopic studies show that the ore-forming fluid is dominated by magmatic water,and the ore-forming material has the characteristics of mixed crust and mantle sources,which is similar to that of the Dahuabei intrusion,which has both crust and mantle sources.Mineralization and diagenesis may be homologous.(6)The Hadamengou gold deposit is a typical gold deposit related to(alkaline)intrusion,which named IRGD.The formation of this deposit have close connections with the Dahuabei intrusion in the Hercynian and the Shadegai intrusion in the Indosinian.Its possible mineralization mechanism is: a large number of ore-bearing fluids dissolve in the late magma crystallization?fluids migrate along the EW structure and reflects with the surrounding rock?physical and chemical conditions change?mineral precipitation and the formation of the deposit in a favorable position.The lowest depth of deposit formation is 3.94 km.