Genetic Mechanism of the"Yucheng-Type"High-Grade Skarn Iron Deposits
The discovery of high-grade skarn iron deposits in the Qihe-Yucheng area of northwestern Shandong Province is a significant breakthrough for iron prospecting in China.It is expected to become another potential important base of high-grade iron ore resource in Shandong Province after Laiwu,Jinling,and Jinan areas.Un-like traditional skarn iron deposits hosted in the contact zone between intrusions and carbonate rocks,the Litun iron orebodies in the Qihe-Yucheng area are hosted in the Carboniferous-Permian coal-bearing strata.The high-grade iron orebodies have a sharp contact with the surrounding rocks,which have been changed to horns in a large range.We attribute the occurrence of the iron orebodies in the Carboniferous-Permian coal-bearing strata far from the contact zone to the extremely low thermal conductivity of the overlying coal rocks,which allow the hydrothermal fluid to maintain a high-temperature state and long-distance migration.The formation of the Litun iron deposit may be ascribed to the rapid precipitation of magnetite due to decreasing temperature and salinity caused by the mixing of high-temperature magmatic fluid and low-temperature meteoric water.In addition,strong albitization commonly occurs near ore bodies,leading to the loss of iron in the dioritic rocks,which lays an important material foundation for the exsolution of iron-rich fluids and the formation of high-grade iron ores.Finally,we propose that the mantle-derived"highly differentiated"diorite and hypabyssal emplacement is fa-vor for the exsolution of magmatic fluids,and is also prerequisites for the formation of the Hanxing-type iron deposit.
skarnhigh-grade iron oresfluid transportationalbitationYucheng-type
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