Geological Characteristics And Discussion On The Genesis Of The Langshan Huo Geqi NO.2 Deposit In Inner Mongolia

The Huogeqi deposit,located in the western segment of the north margin of the north China Craton,is a large-scale Cu polymetallic deposit in Inner Mongolia.There are three main medium-large scale ore deposits in the mining area and the NO.2 deposit is in the north of the mining area.The ore bodies are controlled by the second rock formation of Langshan group and are in concordance with the occurrence of stratum with the same shape of fold.Its protolith is ore-bearing sedimentary formation which is a set of argillaceous,chemical sedimentary,carbonate and clastic rocks.The orebodies are characterized by obvious zonation both in vertical and horizontal direction,which is a typical feature of sedimentary geochemistry differentiation.The total rare earth elements(REE)of magnetites are very low,and light and heavy rare earth elements had evidently differentiated.Magnetites are characterized by obvious enrichment of light REE and depletion of heavy REE with positive Eu and La anomalies,and high ratio of Y/Ho,which indicates that ore-forming fluids are mixed by seawater and hydrothermal fluid.The characteristics of rare earth elements pattern of magnetites are similar with that of ores,which reveal the genetic relationship and homology between them.Trace elements of magnetites have consistent distribution trend and great variation range,which reveal that they underwent relatively simple mineralization and different degrees of late hydrothermal reform.Magnetites have very low V and Cr contents,which indicates that magnetites were irrelevant with magmatic differentiation,and this also excludes the possibility of that the magnetites belong to volcanic rock type and accessory mineral type.The value of Co in magnetites range from 0.403 to 2.5103×10-6,which deviates significantly from magmatic iron deposit(30?10-6)and skarn iron deposit(70?247×0-6).The major ore-host rock is termolite whose protolith iscarbonate rock,which depicts that the deposit is a sedimentary reconstructive deposit.Namely,magnetites were derived from the reconstruction of early sedimentary sulfides by late geological processes.The layered sulfides are enriched in heavy sulfur and the ?34S are concentrated in the range of+10.6‰ to+23.5‰,with a mean value of 16.68‰.The ?34S in barite sample is+22.2‰,which indicates that the sulfur come from the sulfate in seawater.The ?34S of the vein sulfide are lower than layered sulfides which may cause by that sulfides formed in deposition period have changed remarkably during metamorphism and magmatism.On the whole,the ?34S ranges from+8‰ to+20‰,with great varying range and no obvious peaks,presenting a wave distribution,which should be the result of homogenization of sulfur isotope by regional metamorphism and thermal metamorphism.Based on previous studies,the geological and geochemical characteristics of No.2 ore deposit in Huogeqi ore field indicate that the No.2 ore deposit is an exhalative sedimentary deposit which were reformed by late regional metamorphism and contact metasomatism.