Geological And Geochemical Characteristics Of Yuqia Rutile Ore And Ore-controlling Factors Research,Qing Hai Province

In recent years,Yuqia eclogite-type rutile deposit is the first ultra-large rutile deposit which was found in the northern margin of Qaidam basin,Qinghai province.It is large in scale,rich in grade,with great exploitation and resource potential.It was generated by ultrahigh pressure metamorphism,and in the space domain,it was related to the ultrahigh pressure metamorphism of eclogite.The discovery of the deposit provides a direct basis for further exploration the rutile deposits on the northern Qaidam UHP metamorphic belt.In order to study the metallogenic model of the rutile deposit,this article researched the eclogite in Yuqia area from the petrography,rock geochemistry and mineral chemistry.Based on the compisitional zonation of garnet,distribution and type of mineral inclusions,Yuqia eclogite has undergone three metamorphic evolution stages:pre-eclogite facies stage,eclogite facies stage and late retrograde amphibolite facies stage.The eclogite facies stage can be divided into three sub-stage of early-,peak-and early retrograde-eclogite.The eclogite facies stage is the main stage of rutile mineralization,but part of the rutile was turned into ilmenite and sphene and other titanium minerals in the late retrograde amphibolite facies,and it is not conducive to the preservation of rutile.From the field geological observation,combined with the content of Ti O₂in eclogite,the Yuqia eclogite is divided into two types of high-Ti group(Ti O₂>2%)and low-Ti group(Ti O₂=1-2%).The geochemical analysis showed that the high-Ti group is derived from the basalts with OIB properties in the source area,while the source area of low-Ti group is came from the basalts with MORB characteristics.Combined with the marble protolith age which interlayer output with the eclogites,we think they should be homologous,and may be an island arc basalt from the fore-arc or back-arc basin,influenced by different magma evolution.And the Mg^#(0.38-0.44)in the high-Ti group is lower than that the low-Ti group.It is showed that the magma of high-Ti group have the characteristics of high degree of evolution and low degree of contamination by continental crust.In combining of petrography,petrology and geochemistry,we have concluded that titanium mineralization in Yuqia rutile deposit should have been experienced four stages:primary Ti enrichment in protolithes of eclogites,titanium mineralization during deep subduction,titanium mineralization during exhumation and rutile mineralization in fluid activity.Deep subduction stage is the most favorable stage of rutile mineralization in the period before and after,while the destruction of rutile is detrimental to the preservation of rutile during exhumation.The rich-Ti basic rocks with high TFe(13-15.48%)and depleted Si(45.9-49.83%)content are the source of the ore shoots in the eclogite-type rutile deposits.The field prospecting signs are dark brown massive eclogites,the higher the freshness of the eclogite,the more self-shaped mineral,the more favorable the formation of rutile rich ore with intergranular output.