Evolution Mode for the Ore-forming Fluid System of the Laozuoshan Skarn-Magmatic Hydrothermal Vein Gold Deposit,Heilongjiang Province,China

The Laozuoshan gold deposit, located in the Jiamusi Massif uplift zone of eastern Hercynian Xingmeng geosyncline, is hosted in Hercynian granitoids, and Yanshanian granodiorite and diorite porphyrite, which has been obviously controlled by the fracture.This gold deposit belongs to a skarn-magmatic hydrothermal vein deposit, and the hydrothermal ore-forming process can be divided into four stages.For the fluid inclusions from the former three stages, their homogenization temperatures range from 287℃ to 472℃, from 156℃ to 412℃ and from 155℃ to 412℃, while their salinities vary from 3.21% NaCl equiv to 50.85 wt.% NaCl equiv, from 2.73% NaCl equiv to 42.65wt.% NaCl equiv and from 2.73 wt.% NaCl equiv to 8.13 wt.% NaCl equiv, respectively.The (Fe) Au mineralization was mainly occurred in the stageⅡ, while the Au (Cu) mineralization was dominated by the stage Ⅲ, and this stage serves as the main mineralization stage.The heat source for the formation of this gold deposit was provided by the original hydrothermal magmatic waters, the deposition of Au,Cu, and Fe was caused by the escape of CO₂ and H₂S, as well as the input and mixing of meteoric water.Thus, the rapid precipitation of sulfides and gold was caused by the fluid unmixing, boiling and mixing.The fractures were infilled with Hercynian gneissic granite and gneissic granodiorite, and Yanshanian granodiorite and diorite porphyrite, supplying the ore-forming space.Therefore, the evolutionary processes observed in the ore-forming fluid system of this deposit is different from the presented regional crustal continuous mineralization mode, orogenic gold deposits and epithermal gold deposits formed in the geodynamic settings.