The Magma Conduit System Of XiShiMen Iron Ore Deposit In Wuan,HeBei Province

HanXing-type iron deposit,located in the south of HeBei province,is an important large-scale iron ore concentration area which is known for its reserves and high-grade ores.Concerning the genesis of Hanxing-type deposit,dispute still exists to date.The mainstream academic viewpoint ascribes the formation of the deposit to contact metasomatism,while others associate it with hydrothermal process.We focus our research on Xishimen iron deposit-the largest deposit in our working area,try to make clear the spatial distribution characteristics concerning the component,texture and structure of iron ores,and to provide theoritical instructions for exploration of similar ore deposits.The intrusions related to ore deposits are a complex of basic—neutral—alkaline rocks.The complex can be broadly divided into three magmatic belts from west to east.These three magmatic belts in turn are hornblende diorite,diorite and syenite.They are named Fushan,Wuan,Hongshan.The stratum in this area is carbonate rock of Middle Ordovician Majiagou group.The iron ore bodies are always in contact zone between carbonate rocks and intrusions.Some iron ore bodies are in the cracks of intrutions or carbonate rocks.Through the study on the XiShiMen deposit,author believes that the iron ore body in XiShiMen is a magma-type deposit instead of skarn-type.The ore magma separated from the magma and moved to the upper crust,and located in the contact zone between intrusions and carbonate rocks.The evidence of ore body injecting into wall rocks in this area is very common:The iron ore bodys are not only in contact zone between carbonate rocks and intrusions,but also in the cracks of intrutions and carbonate rocks;Under the mine,the flow structure of iron ore body is visible,reflecting injection genesis;The boundaries of ore bodies and wall rock are very distinced and straight,the baked side of the wall rock is visible;The structure of ores include massive,vesicular and almond-shaped;In the mircroscope,the texture of magnetite is euhedral-subhedral,reflecting crystllization genesis;Small particles of silicate minerals inclusions are visible among the magnetite particles.These phenomena can demonstrate the injection of the iron ore body,provide strong evidence for the presence of iron ore magma.Through the research on XiShiMen iron ore deposit,we can summarize the characteristics of iron ore deposit.Suggesting that the iron ore magma contains a large number of the fluid which is rich in F,Cl,and strong sodium phenomena of the wall rocks surrounding the ore bodies,reflecting iron ore magma is also abound in alkali,especially sodium.A series of Neocathaysian fracture structures are in the southest of this area,they provide a good space for magma and ore magma.The content of titanium oxide as a geological thermometer is used to determine the transportation channel of ore magma,and suggest that it is located in the northeast of the ore field.