Abstract:

The studied area is located in the middle section of the north margin of North China craton, which is one of the most important gold and nonferrous metal metallogenic belts. In the Xiaotazigou ore district, the hosted rocks of gold deposit are the Archean metamorphic complex of Xiaotazigou formation, and the orebodies are primarily hosted in EWstriking and NEstriking fractures, while Beidashan monzonitic granite body is closely associated with metallization. The ore natural type of 1# vein is the quartz vein type; its economic value is the highest in the ore district. Fluid inclusions of quartz crystals in 1# vein can be classified into types of aqueous twophase, CO2rich three phase and pure gas. The salinities of fluid inclusions range from 2.06% to 11.72% NaCleqv，concentrating in three ranges of 2.06%3.37% NaCleqv，4.69%6.97% NaCleqv and 9.86%11.72% NaCleqv. The densities of fluid inclusions range from 0.689 to 0.977 g/cm3. The homogenization temperatures of fluid inclusions range from 174 ℃ to 348 ℃，concentrating in two ranges of 302348 ℃ and 174187 ℃. During the early oreforming stage, the oreforming fluids were characterized by high temperature, low salinity, and the coexistence of CO2rich three phase and aqueous twophase. The reason for the coexistence is that the mixture of two different kinds of fluids caused nonuniform capture. During the middlelate oreforming stage, the oreforming fluids were characterized by the fall in temperature，and the rise in salinity. The abrupt fall in temperature resulted in boiling characterized by CO2 loss, from which the salinity and the density of remnant fluids were raised. According to the diagram of coexistence surface，the oreforming pressure can be calculated and it is in the range of 1628 MPa, the oreforming depth is in the range of 1.62.8 km. In contrast to other orogenic gold deposits worldwide, Xiaotazigou gold deposit is defined as epizonal orogenic gold deposit and the intracontinent collision was its metallogenic dynamic background.

Key words: nonuniform capture, boiling, fluid inclusion, epizonal orogenic gold deposit, Xiaotazigou 1# vein, Chaoyang