Link Between Xinyu Iron Deposit And "Snowball Earth"

The banded iron formation re-emerged in the Neopraterozoic nearly billions of years after its disappearance from the Mesoproterozoic.This is considered an important symbol of the"Cloudball Earth"event.The Xinyu iron deposit,located in the central Jiangxi Province,is a Neoproterozoic iron formation that was deposited in the Xiafang Formation of the Nanhua System.Although Xinyu iron deposit has a high degree of research,the issues about the genesis mechanism have under debated and not yet been determined,and its relationship with glacial effects is still contriversal.Base on analysis on major andtrace elements(including rare earth elements),it is supposed that the material sources of the Xinyu iron ore are mainly the endmembers of submarine hydrothermal and terrigenous debris.The hydrothermal fluid on the sea floor continues to provide ore-forming materials,and the proportion of terrigenous clastics gradually decreases from the Gujia conglomerate section to the iron-bearing rock section.It is transferred from land to submarine sediments by glaciers and ice rafts.The rare earth element Ce anomaly is not obvious,which indicates that the oxygen fugacity in seawater is not as high as moden sea water,which is consistent with the situation of the"snowball earth"hypothesis.Due to the ice seal in the Neoproterozoic sea,the ocean floor cannot be supplemented with oxygen from the atmosphere,so it gradually turns to a reduced state,and a large amount of Fe²⁺will be accumulated in the seawater.After the ice seal is lifted,the seawater oxidation results in the deposition of Fe elements.This mechanism is"Blood Falls"phenomenon has been verified.The Y/Ho ratio of the rare earth element in the iron ore sample shows that the terrigenous debris from the surface has undergone considerable weathering alteration,which proves that the iron ore was formed in the interglacial period.Additionally,with comprehensive stratigraphic comparison,Xinyu iron ore exhibits a glacial sedimentary conglomerate section similar to the Chang'an Formation,as well as a manganese-containing layer similar to the Fulu Formation above the iron formaiton.This is due to the climate rebound and the proliferation of large numbers of organisms.Therefore,it is inferred that the Xiafang Formation is an interglacial deposition after the Sturtian glacial period.Combining the above arguments,this contribution proposes a modified model of the ore-forming mechanism of the Xinyu iron ore,and summarizes the ore prospecting signs and rules.Because its mineralization is closely related to the"Snowball Earth"event,the Gujia conglomerate section of the Xiafang Formation,which marks the glacier movement,can be used as an ore prospecting indicator for Xinyu iron ore in future.The main source of iron is hydrothermal fluid from sea floor.Consequently,the Xinyu iron depoist is closely related to plutons in the area(especially the Jinning period pultons).