Chemical Stratigraphic Study On The Sailinhudong Group Of Damao Banner In Inner Mongolia

The Bayan Obo REE-Nb-Fe deposit,located in the central part of Baotou City,Inner Mongolia,is a world famous giant polymetallic deposit.Widely concerned by the Geosciences at home and abroad,However,the material composition and formation history of the Bayan Obo deposit are very complicated.There is still much controversy over the metallogenic mechanism and age.One of the main reasons is that there are great divergences in the understanding of the formation age of the Bayan Obo Group in the ore-bearing strata.The Sailinhudong Group in this area is a well-developed and well-preserved sedimentary formation of carbonate rocks.Like the Bayan Obo Group,it is unconformity on the Early Precambrian metamorphic basement.They have similar rock assemblages and similar tectonic settings.It suffers only slight deterioration.It can be well compared with the Bayan Obo Group.Furthermore,new constraints on the formation age of the Bayan Obo deposit are put forward.Due to the limited application potential of chronostratigraphy and biostratigraphy in these disputed sedimentary stratigraphic correlation and division.Chemical stratigraphy has become an important means of correlation and division of controversial strata such as the Sailinhudong Group.In this paper,systematic studies on inorganic carbon isotopes and rare earth element chemical stratigraphy of carbonate rocks of the Sailinhudong Group are carried out.Compared with the chemical stratigraphic framework of typical Proterozoic geological profiles,the age attribution of the Sailinhudong Group was determined.The sedimentary environment is restricted by its evolutionary characteristics.The following innovative achievements and understandings have been achieved:1.For the first time,the evolutionary curve of the carbonate rocks of the Sailinhudong Group in Inner Mongolia has been established.The range of variation of the value of?¹³C_carbarb ranges from-3.4‰to+1.2‰.There are two negative drift events.The first negative drift event occurred in the middle of the second parotid group.The maximum negative deviation is-3.4‰.It may be caused by diagenetic alteration or the importation of terrigenous materials.The second negative drift event occurred at the boundary of interval II and interval III.Quickly negative drift to-1.3‰,it is closely related to oxidation events.2.For the first time,the evolution characteristics of water body during the sedimentary period of the Sailinhudong Group were established.There is a trend of change from atypical seawater to typical seawater to atypical seawater.The evolution trend of Ce anomaly is from decreasing to increasing?the second group:Ce_N/Ce^*_N=0.72⁰.87;the third group:Ce_N/Ce^*_N=0.69⁰.92;the forth group:Ce_N/Ce^*_N=0.73¹.05?.It is proved that there is an oxidation event.3.The carbonate rocks of the Sailinhudong Group recorded the variation trend of relatively stable carbon isotopes and the sedimentary environment of relative reduction.By comparing with the chemical stratigraphic framework of typical Proterozoic geological sections.It is determined that the Sailinhudong Group was deposited in the Mesoproterozoic.