Abstract: Abstract: The Jingshansi iron deposit in Henan Province is located in the southeastern part of the North China Craton. The orebodies occur in nearly bedded and lenticular forms, and the iron ores are predominantly banded, with minor massive ones. Taihua Group Tieshanmiao Formation marbles are developed as main wall rocks and interlayers among the orebodies. Geochemical studies of carbon, oxygen and silicon isotopes of the ore deposit were carried out to investigate the ore?forming fluid nature and its potential sources. The results show that δ13CV?PDB values of ore?forming calcite range from ?5.2‰ to ?1.4‰, δ18OV?SMOW values range from 8.5‰ to 16.9‰, δ13CV?PDB values of carbonate host rocks calcite range from ?1.0‰ to 1.6‰, and δ18OV?SMOW values range from 20.3‰ to 23.4‰, the C and O isotope evolution indicates that drastic water?rock interaction took place at the ore?forming stage, and isotope exchange took place between ore?forming fluids and carbonate host rocks. The carbon isotope components were mainly provided by the marine carbonate rocks through dissolution, influenced by middle?low temperature alteration. The characteristics of δ18OH2O indicate that the hydrothermal solution is?the?mixture?of?magmatic?water?and?seawater.?The δ30Si NBS?28 values of iron ore quartz range from ?1.9‰ to ?0.4‰, and the δ30Si value of leptite quartz is 0‰, which indicates that the silicon isotope were derived from volcanic?exhalation. The Si isotope fractionation took place in the ore?forming process. A comprehensive analysis shows that the Jingshansi iron deposit?was?formed?in?a submarine?volcanic?eruptions?sedimentary?environment?in Precambrian.