Abstract: The Luozuoshan gold deposit is located in the north-center of Jiamusi massif of Eastern of Xingmeng orogenic belt, which is a large deposit in the Jiamusi gold metallogenic area. The ore bodies are hosted in the NW and NWW trend extension fractures and the contact zone between the granite and calcareous marble and gneiss, and the mineralization is closely associated with skarn. According to the field and laboratory studies, the authors divided the mineralization process into five stages, i. e, skarn, oxide, early sulfide, late sulfide, and quarts-calcite stages. The inclusion petrography shows that the fluid inclusions are mainly composed of daughter-crystal bearing inclusions, gas-liquid inclusions (incl. rich liquid and rich gas inclusions), pure liquid inclusions, and pure gas inclusions. The measured temperatures indicate that the homogeneous temperatures were 448-462℃, 240-509℃, 166-480℃, 118-360℃, and 57-230℃ from early to late respectively. The salinities of mineralization were w(NaCl)9.21%-10.37% in skarn stage, 1.73%-13.77% in oxide stage, 1.73%-23.71% and 23.64%-39.66% in early sulfide stage, 3.05%-6.44% in late sulfide stage, and 1.73%-11.95% in quarts-calcite stage. During the oxide stage, the initial ore-forming fluid was of high temperature, low-medium salinity, and rich in CO₂, H₂O and a little CH₄. The fluid boiled, resulting in the escape of CO₂ and formation of magnetite. The fluid continued to boil at the early sulfide stage, which caused the increase of pH value, the transformation of the fluid from oxidation to reduction, and the deposition of gold and arsenopyrite. With the temperature decrease at the late sulfide stage, the low temperature minerals precipitated, such as galena, sphalerite, and gold. It is presumed that the Laozuoshan gold deposit is a skarn type gold deposit.

Key words: Jiamusi massif, Laozuoshan gold deposit, fluid inclusion, evolution of fluid, genesis of deposit