Abstract: Abstract：The Tongguanshan copper field in Tongling, Anhui, is one of the typical skarn orefields in the middle-lower Yangtze Valley iron, copper, sulfur and gold metallogenic belt of China. The Xiaotongguanshan copper deposit located in the Tongguanshan copper field is related to the Tongguanshan quartz monzodiorite. The formation of the copper deposit progresses through the skarn stage, quartz-sulfide stage and quartz-carbonate stage. Based on the geological setting, mineralogy and tectonics of the deposit, combined with the hydrogen, oxygen, carbon, sulfur and silicon isotopic compositions and REE geochemistry of the ore-forming fluids, this paper deals mainly with the sources of water, silicon and sulfur in the ore-forming fluids and their evolution. The results show that the ore-forming fluids were dominated by magmatic water at the early stage, whereas with an increase in meteoric water entering the mineralizing system, the meteoric water might predominate at the late stage. Sulfur has two sources, i. e. strata and magmatic hydrothermal fluids, with the latter predominating. Silicon shows the features of deep-seated magma or magmatic hydrothermal fluids. Chondrite-normalized REE patterns are right-inclined, and the REE distribution patterns for skarn and ores are similar to those of the Tongguanshan quartz monzodiorite, which indicates that the hydrothermal fluids of the skarn deposit in the study area were mainly derived from dioritic melt.