The Characteristics Of Ore-forming Fluids And Geological Significance From The Yinan Gold Deposit, Shandong Province

As a typical skarn deposit in the western Shandong Province, the Yinan gold deposit is located on the west side of Yishu fault zone. It includes the Tongjing and Jinchang ore districts which are 6 km away from each other. The deposit is controlled by magma, strata lithology, wall rock alteration and structure. The location of the ore-forming intrusions were controlled by the intersecting places between the NW and NE or the NW and NEE trending fault structures .The ore-controlling and ore-bearing structures mainly include contact zone, interlayer fractured zone and unconformity structure,etc. The metalogenic processes can be devided into the anhydrous skarn stage, the hydrous skarn-magnetite stage, the oxide-sulfide stage and the carbonate stage. In the recent years, new ore layers have been discovered, but the investigations on the fluid inclusions of the deposit which restrict the ore genesis and metallogenic laws is urently needed.Based on the fluid inclusion study, this paper made further discussions on the source of ore-forming materials and ore genesis of the deposit. Petrographic observations and temperature results indicate that the main type of fluid inclusions are aqueous inclusions, CO2-H2O inclusions, crystalline melt inclusion and daughter mineral-bearing multiphase in four mineralization stages. Melt inclusions were recognized in garnet, epidote and quartz. In the first and second mineralization stage, the ore-forming fluid is characterized by high temperature and high salinity , homogenization temperature is 430℃～510℃and 330～390℃respectively with salinity 56.7 wt% NaCl and 2.2～53.5 wt% NaCl respectively, indicating the fluid activities during Fe mineralization; In the third mineralization stage, the ore-forming fluid is salinities(6.45～53.5 wt% NaCl ); In the last stage, the homogenization temperature ranged from 130℃to 190℃, with salinity from 2.07 to 15.76 wt% NaCl. The mineralization occurred under the epithermal conditions of 0.6～1.7km.The appearance of the melt inclusions in garnet and epidote is the evidence of magmatic skarn.The assemblage of different fluid inclusions and the evolution characteristics of fluid inclusion show that fluid immiscibility is the main cause for mineralization. The composition of H and O isotopes shows that the ore-forming fluids were mainly magmatic hydrothermal fluids and were mixed with meteoric water during the later mineralization stage.