The Wall Rock Alteration And Fluid Inclusion Study At Bilihe Gold Mine, Inner Mongolia

Bilihe gold mine lie in the north edge of Huabei tectonic plate. As an important gold mineralization area, it is in southern subduction zone closing to Huabei plate. From pervious works, five mineralization alteration zones were cycled in Bilihe mining zone: zone No.1 (exploited), zone No. 2 (new reserves found), No.26 vein, No.23 vein, and No.22 vein.Geological background of deposit of the mining zone have been investigated in detail. Rock samples from 201 mine body of zone No.1 were studied through microscope and Near-Infrared spectrometer to identify the types of alteration, spatial distribution, and the relationship with gold mineralization. Rock phase of fluid inclusion, homogeneous temperature, and salinity have been studied from zone No.1 and zone No.2. Considering with the results of Geological background, alteration character, and fluid inclusion, the mine forming characters and prospective mines have been discussed. Results are listed below:(1) Wall rock of mine body: Zone No.1 include andisite, granite-diorite-porphyrite, granite-porphyry; Zone No.2 include sub-volcanic rock (granite-diorite-porphyrite and monzonite-granite-porphyry) which is controlled by structure of north-west and north-east and minor volcanic clastic rock.(2)Alteration of wall rock in mining zone includes chloritization, silicification, sericitization, argillization, tourmalinization, and carbonatation. Chloritization happened around mine body, Silicification, sericitization, argillization are in the same places with gold mineralization in many areas,and distribute along structural zone and contact zone of stratum, and stratigraphic crossing and contacting layer between rock body and stratum have strong silicification, sericitization, argillization.(3) The study of high abundance and small size fluid inclusion from 5,6 middle parts of No.1 mining zone show that they are usually NaCl-H2O inclusion (gas phase inclusion and gas-fluid inclusion) and crystal inclusions. There are three peaks appearing in uniform temperature at 220 C-280 C, 160 C-220 C, and 120 C-160 C. It suggests that the mineralization temperature is 160-220 C, and salinity<5%. (4)Considering gold mineralization in the mine zone and Near-Infrared spectra data, the No.22 vein and south-east river of No.2 mine zone could be the prospective mine zone.