Mineralogical Characteristics And Geological Significance Of Typical Minerals In The Huanggangliang Iron-Tin Polymetallic Deposit, Inner Mongolia

The Huanggangliang iron-tin polymetallic deposit is one of the most important iron-tin deposits in north China,which is located in the southern section of the Great Xing’an Range.It forms the main ridge metallogenic subzone of the Great Xing’an Range with the surrounding lead-zinc,tungsten-molybdenum polymetallic deposits.Most ore bodies in the deposit are mainly stratified and like stratified,which have similar orebody occurrence characteristics to the Dongguashan copper deposit in Tongling,Anhui province,the Yongping copper deposit in Jiangxi Province and the Dabaoshan copper-iron polymetallic deposit in Guangdong Province.At present,the formation of the bedded or similar bedded ore body is still controversial.This paper discusses the genesis of the deposit by studying magnetite,pyrite and sphalerite and their isotopes.(1)In view of the differences in the production environment and mineral composition of the Ⅰ,Ⅲ and V mining areas,the magnetite in the three mining areas was analyzed by EMPA and LA-ICP-MS.The test results show that there are obvious differences in crystallization temperature of magnetite in each mining area.T-magnetite(Ⅲ)<T-magnetite(V)< T-magnetite(Ⅰ)(“T” stands for temperature),which are consistent with the formation temperature of magmatic hydrothermal skarn magnetite.In terms of oxygen fugacity and water-rock reaction,the oxygen fugacity is the highest in zone Ⅰ,the second in zone Ⅲ,and the lowest in zone V.The water-rock reaction is strong in zone Ⅰ,while the water-rock reaction has a long time in zone Ⅲ.The intensity of water-rock reaction changes from strong to weak.(2)Pyrite divided into vein(Py1)and disseminated(Py2)pyrite has undergone detailed petrographic observations like sphalerite which is disseminated and laminated.The results of EMMA and LA-ICP-MS showed Co/Ni > 1 for Py1 and Co/Ni <1 for Py2.Combined with petrographic characteristics,Py1 developed in quartz veins interspersed with skarn,Py2 co-existed with chalcopyrite and sphalerite.Therefore,pyrites of both types belong to hydrothermal origin,and Py2 were formed in the late hydrothermal stage with lower temperature.The geological thermometer of sphalerite shows that the formation temperature of sphalerite ranges from 297℃ to 323 ℃ in medium-high temperature environment,which is consistent with the mineralization temperature of sulfide stage in typical skarn deposits.In addition,the Cd/Fe and Cd/Mn ratios of sphalerite also indicate that magmatic hydrothermal process was involved in the mineralization process.(3)The hydrogen and oxygen isotope characteristics of quartz and magnetite indicate that the ore-forming fluid is mainly magmatic fluid,and meteoric precipitation is involved in the late stage.The S-Pb isotope of metal sulfide shows that the sulfur isotope has the characteristics of deep source of sulfur and the addition of crustal sulfur,and the lead is the mixed source of crust-mantle.(4)Combining geological,elemental and isotopic geochemical characteristics,the Huanggangliang iron-tin polymetallic deposit is considered to be a skarn type deposit related to magmatic hydrothermal solution.