Abstract:

The Shangdaohui Mo deposit is located in the Xiong’ershan-Waifangshan region which is in the southern margin of the North China Craton. The orebodies, controlled by the secondary fault of the Machaoying fault, occur as veins and are hosted by the Mesoproterozoic intermediate to felsic volcanic rocks of the Xiong’er Group. The major metallic minerals are molybdenite and pyrite. The silicification, K-felsparization and carbonatization are the main hydrothermal alteration types. The hydrothermal ore-forming process can be divided into three stages, quartz+pyrite stage (early stage), quartz+molybdenite+polymetallic sulfide stage (middle stage) and quartz+calcite stage (late stage). Three types of fluid inclusions can be identified in the Shangdaohui Mo deposit, including aqueous (W-type), CO₂-rich (C-type), daughter mineral-bearing (S-type) fluid inclusions. The early stage quartz contains mostly W-type, C-type and minor S-type fluid inclusions, the middle stage quartz contains C-type, W-type and S-type fluid inclusions, and the late stage calcite only contains the W-type fluid inclusions. The homogenization temperatures of early-stage fluid inclusions range from 210  ℃ to 390  ℃, with salinity of 1.0%-13.4% and 27.2%-33.2%. The middle-stage homogenization temperature is 180℃ to 300 ℃, with salinity of 0.3%-14.1% and 27.3%-28.5%, and the last-stage homogenization temperature ranges from 120 ℃ to 220 ℃, with salinity 0.1%-14.2%. The ore-forming fluid evolved from carbonic to aqueous from early to late mineralization stage. Fluid boiling occurred in both early and middle stages, and resulted in release of CO₂, which caused the precipitation of the MoS₂ and other sulfides. Trapping pressures estimated according to the C-type fluid inclusions are 148-371 MPa and 108-383 MPa in the early and middle stages, corresponding to metallogenic depth of 5-14 km.

Key words: Shangdaohui Mo deposit, K-feldspar-quartz vein type, geological characteristics, fluid inclusion, Xiong’ershan region, western Henan