Abstract:Based on the study of the petrology, mineralogy, structural geology and fluid inclusion of the Dafulou ore deposit in the Dachang ore field, the ore deposit geology and ore-forming fluids were analyzed. It shows that there are five main hydrothermal alteration types in the Dafulou ore district, namely the silicification, carbonate, sericite, pyrite and pyrrhotite. The mineralization types are composed of the stratiform type, interlayer type and stockwork type. The ore textures present as metasomatic texture, euhedral-subhedral granular texture and solid solution texture. The ore structure consists of massive structure, dissemination structure, fine veined structure, stockwork structure and brecciated structure. Four ore types are recognized, namely the disseminated ore, dense massive ore, veinlet ore and brecciated ore. Six types of fluid inclusions are determined, i.e. the single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO₂-rich fluid inclusions and solid(s)-bearing fluid inclusions, all of which form in three dominant temperature scopes, 120-150, 230-270, 350-460 °C. But, the majority of them form in the high temperature environment (350-460 °C). The tectonism plays an important role in the mineralization, which usually controls the scale, occurrence and shape of the Sn orebody. There are four types of hydrothermal fluid systems, H₂O-NaCl-CaCl₂, H₂O-CaCl₂, H₂O-NaCl-MgCl₂ and H₂O-MgCl₂. Similar to the other ore deposits in the Dachang ore field, there also exists the multiple source of ore-forming fluids. Overall, the Dafulou ore deposit should be the result of the crust-mantle interaction.

Key words: fluid inclusion; mineralization; Sn-polymetallic deposit; Dafulou; Dachang