TThe Yamansu iron deposit developed in Eastern Tianshan, Xinjiang, is one of the typical iron deposits hosted in submarine volcanic rocks in this area. Duo to the controversy on the genesis of the skarn, some researchers suggest it is of submarine type, while others consider it is a skarn deposit. This debates has disturbed the determination of the key metallogenetic factors and the prospecting guidelines. In order to study the genesis of the skarn in the Yamansu iron deposit, in this study, we have obtained the SHRIMP U-Pb ages of the zircons from the diabase dyke which cuts the skarn bodies, the major elements compositions of the volcanic rocks, volcanic-sedimentary rocks and skarn by XRF, and the mineral chemistry of various garnets by EPMA. The age data of the diabase dyke is 335Ma, which indicates the ages of the skarn and iron mineralization are earlier than 335Ma, being coeval with the volcanic activities. Under the microscope, we have found albite in the volcanic rocks has been changed into prehnite initially, then into garnet. There are two stages of garnets. The earlier garnet is mainly brown andradite, while the later garnet is colourless grossular-andradite intergrown with magnetite and pyrite. In view of no obvious genetic relationship between the skarn and intrusive bodies, we suggest that the skarn in the Yamansu iron deposit belongs to the “general skarn”, and this deposit is an iron deposit of submarine volcanic type.