Abstract:

The Manzhouli area located in the northeastern part of Inner Mongolia is the most important AgPbZn metallogenic province in the Derbugan metallogenic belt. In this paper, the authors systematically studied the fluid inclusions of the AgPbZn deposits and discussed their ore genetic types with the Erentaolegai and Chaganbulagen deposits as examples. In the Erentaolegai Ag deposit, the fluid inclusions are characterized by aqueous twophase inclusion, with homogeneous temperatures of 242 to 334 ℃ (averaging 265 ℃), salinities of 173 wt% to 448 wt% NaCleqv (averaging 270 wt% NaCleqv) and densities of 072 to 084 g/cm3 (averaging 080 g/cm3). In the Chaganbulagen AgPbZn deposit, fluid inclusions can be classified into types of aqueous twophase, CO2bearing and pure CO2; their homogenization temperatures, salinities and densities range from 179  to 367 ℃ (averaging 261 ℃), 223 wt% to 687 wt% NaCleqv (averaging 435 wt% NaCleqv) and 065 to 091 g/cm3 (averaging 082 g/cm3), respectively. The oreforming pressures of the Erentaolegai and Chaganbulagen deposits varied from 13 to 26 MPa with an average of 18 MPa and from 15 to 46 MPa with an average of 25 MPa, respectively, corresponding to oreforming depths of 05 to 10 km with an average of 07 km and 06 to 17 km with an average of 09 km, respectively. The oreforming fluids of the both deposits were characterized by lowtomoderate temperature, low salinity and moderate density. The oreforming fluids of the Erentaolegai and Chaganbulagen deposits generally belonged to H2ONaCl and H2OCO2CH4NaCl fluid systems, respectively. The oreforming fluid of the Erentaolegai Ag deposit was mainly composed of meteoric water, and its genetic type belonged to epithermal. The oreforming fluid of the Chaganbulagen AgPbZn deposit consisted mainly of mixed water between magmatic water and meteoric water. And its origin belonged to epithermaltomesothermal lode deposit, and immiscibility or boiling action of oreforming fluid was the dominant factor for silver, lead and zinc deposition. The AgPbZn deposits were closely related to the volcanic and/or subvolcanic hydrothermal solutions of the late stage of the Late JurassicEarly Cretaceous volcanicmagmatic activity. The mineralization period of the AgPbZn deposits in the Manzhouli area was in the Early Cretaceous, those deposits occurred in the Mesozoic intracontinental volcanofault basin with an extensional tectonic setting.

Key words: fluid inclusion, Erentaolegai silver deposit, Chaganbulagen silverleadzinc deposit, ore genesis, Manzhouli area, Inner Mongolia