The hydrogen and oxygen isotopic compositions of water in the ore fluids are related with the initial isotopic compositions of waters and rocks, chemical compositions of rocks, and the ratio of exchangeable oxygen (or hydrogen) atoms in the water to those in the rock (W/R) and the exchanging temperature, Some organic matters may also have some efferts on the isotopic fractionations. A discussion on these problems through the case of Jiaod}ng Rushan gold deposit is presented in this paper.The Rushan gold deposit one of the important quartz-vein gold deposits in the Jiaodong district, is located in the Kunyushan granitic pluton. Initial data on the hydrogen and oxygen isotopic compositions of water in fluid inclusions in quartz from the gold deposit fall within a wide range:δD=-128 to-71 per mil and δ18O=-7.70 to 5.97 per mil, relative to SMOVN. These data compared with those in primary magmatic water and metamorphic water and meteoric waters are shown in figure 1. They have the isotopic compositions ranging from magmatic water to meteoric water, thus suggesting that magmatic and meteoric water should have been mixed in the ore fluids. However that is not the case Fig.2. shows the changes in the δ18O and δD values of magmatic and meteoric waters through equilibnum isotopic exchange with granitic rocks at various temperatures and with various water/rock weight ratios, and suggests that meteoric water alone can evolve into the observed isotopic compositions of the Rushan gold ore fluids by isotopic exchange reactions with granitic racks at temreratmes hetween 200℃ and 350℃.In ether words,a genetic model in which the meteoric water reacts with granitic rocks in different tempcrature and W/R ratio can be used to explain the mmerogenetic mechanism of the Rushan gold deposit. This model is also supported by other geological and geochemical studies of the Rushan gold deposit.As mentioned above, it is not the best method to compare she δD and δ18O values of the ore fluids with those of standard only by means of plotting figure and then determining the origin of the H2O involved in ore mineralizations. Therefore, gread care has to be taken particalarly in the ease to explain the genesis of a deposit using mixing water model because there arc differences in hydrogen and oxygen isotopic compositions between the water of ore fluids and initial water attcr water-rock exchanged. No simple mixing model for origin is likely to explain all or
even most metalliferous ore deposits.