Metallogenic Mechanism Of Neoproterozoic Qulukesay Iron Deposit From The North Tarim Craton

The Neoproterozoic sedimentary metamorphic iron deposit is one type of iron deposit,which occurs once again after the 1 billion year??1800 Ma to?750 Ma?.This type of iron formation is closely related to the Neoproterozoic moraine,which is an important symbol of the Neoproterozoic snowball earth.Different from that of the Archean Paleoproterozoic banded iron formation,which formed in the oxygen deficient deep sea,Maybe,the content of free oxygen in the Neoproterozoic has been very high.Qulukesay iron deposit is manily composed by hematite and associated with Neoproterozoic snowball earth,occurs in Saima mountain,stratigraphic division of North Tarim Basin.Qulukesay iron deposit is consist of three mineralized areas,includes 15 iron ore bodies.The Orebody' s shape occurs as layered and lenticular,which distribution direction concurs with the strata strike.The research object of this paper is the first ore body.This orebody occurrence as lenses and exists in the moraine rock strata,angular unconformity upon the lower Qingbaikouan dolostone strata.The ore itself is an iron cemented moraine,microscopic observation showed that the ore mineral is mainly hematite which content is more than 15%.Zircon U-Pb date limits the formation time of Qulukesay iron deposit between 1800Ma-630Ma.The regional stratigraphic correlation further defines the iron deposit forms in Neoproterozoic Nanhua period.Comparative works of Zircon U-Pb date from ore body and lower bedrock and Petrographic study indicate the clastic material mainly comes from quartz sandstone,which belongs to Duduanshan group,Qingbaikouan system.Qulukesay iron ore is characterized by high Sc,Zr content and low Zn/Co ratio,positive Y anomaly and no Eu anomaly,low Nd isotopic composition.These characters all reflect that the ore-forming elements mainly from the weathering of continental crust.what's more,The characters that metallogenic minerals dominated by hematite,with positive Ce anomalies and without obvious fractionation of Fe isotopic composition,reflect the Qulukesay iron deposit formed in arelative oxygen enrichment environment or an environment which is changing from oxygen poor to oxygen rich.The oxidizers of Fe²⁺are more likely to be free O₂.Therefore,this paper presents a model of the Qulukesay iron deposit named proglacial sedimentation model.We argue that the iron source for the Qulukesay deposit originated from saline water below the glacier cap,which liberated Fe²⁺ from subglacial rocks during the progression of glaciers,and the subglacial Fe²⁺ fluids were oxidized at the edge of the glacier when it slided into the ocean.