Genesis Of The Huogeqi Copper Polymetallic Deposit In The Inner Mongolia And The Regional Crustal Evolution

The Huogeqi deposit of the Inner Mongolia is a famous Cu-Fe-Pb-Zn deposit in China.Lots of geological works have been done during the last two decades and made important progress,but the study on the depositional age of the ore-hosting strata,mineralization age,genesis of deposit and the sources of the mineralization materials had strong controversial.In this paper,we obtained the youngest zircon U-Pb ages of1187 Ma and 1189 Ma from the ore-bearing strata and the emplacement age of 907 Ma from the pyroxene hornblendite,combining with the youngest zircon U-Pb age of 1118Ma from the other scholar,we suggested that the depositional age of the ore-bearing strata is 907 Ma?1118 Ma.Based on the field geological work,microscope observing and the composition of bulk elements and rare elements,we concluded that the deposit type of the Huogeqi depsot is a typical magmatic hydrothermal deposit and the mineral arisen sequence from the early to the late is magnet,pyrite,pyrrhotite,chalcopyrite,sphalerite and galena.Meanwhile,the genesis of the tremolite and diopside is a solution-replacement product of the carbonate rocks.In addition,the ore-bearing hydrothermal has obviously positive europium anormaly.The?³⁴S values in the sulfides have a wide distribution,but part of laminated sulfides yielded negative?³⁴S values,showing the similar with the hydrothermal sulfides,which indicates that the sulfur in the sulfides is the mixture between the strata and hydrothermal solution.The magnet,pyrite and pyrrhotite are enriched of the light Fe isotope and the coarse grain magnet yielded heavier Fe isotopic composition than the fine grain magnet,which indicates that magnet that precipitating from the hydrothermal solution is enriched the heavier Fe isotope than the hydrothermal solution.However,the sulfide that precipitating from the hydrothermal solution is enriched the lighter Fe isotope than the hydrothermal solution.The widespread hornblende garbbro yielded a zircon U-Pb age of 239.6±4 Ma,which is consistent with mineralization age.Meanwhile,this rock has similar Pb isotopic composition with ore,which indicates that the hornblende garbbro is the metallogenic pluton.In addition,the north slope and the south slope of the Langshan Orogenic Belt show a different distribution of U-Pb age and Hf isotope.The age peak of the north slope is the Meso-Neoproterozoic,but the south slope of the Langshan Orogenic Belt is Archean and Paleoproterozoic.In the Hf isotope respect,the peak model age of the north slope is Mesoproterozic,but the south slope is Neoarchean.So we suggested that the Langshan Orogenic should be divided into two parts and the north slope belongs to the Alxa Block,but the south slope is a part of the North China Ctaton.The collision time between the north slope and the south slope of the Langshan Orogenic Belt were during Devonian to Permian.