Characteristics And Genesis Of The Dunde Iron Deposit In Xinjiang Province

The Awulale iron deposit belt which was found in recent years is a new largescale metallogenic belt in western Tianshan. More than ten large scale iron depositswere found successively in this area, like Shikebutai iron deposit, Chagangnuoeriron deposit, Beizhan iron deposit, Dunde iron deposit and so on. And they arousedwide attention of geologists at home and abroad. In order to identify the origin ofskarn and its relationship to the mineralization, the author selected Dunde irondeposit as the main study object, which was obviously controlled by fracture andclosely associated with skarn. Detailed field investigation, microscopic observation,and mineralogical and geochemical analysis have been carried out on theDahalajunshan formation volcanic rocks and Dunde iron deposit, with a focus on theresearch of the skarn genesis and its relation to iron mineralization.The main rock types of Dahalajunshan formation which lies in the continentalmargin arc zone are basalt, basaltic tuff, trachyandensite, basaltic trachyandensite,trachyte, rhyolitic tuff. Trace and rare earth elements characteristics show that thevolcanic rocks might be formed by crystallization and evolution of magmas derivedby the partial melting of mantle wedge and experienced fractional crystallization andassimilation process during their rising and emplacing. The moyrite（A-type granite）in the southwest of the mining area has little relationship with iron mineralization. Itwas formed by crystallization and evolution of magmas through the partial meltingof the lower crust in the post-orogenic stage.The skarn in Dunde iron deposit can be divided into two types: volcanic-metamorphic skarn and hydrothermal metasomatic skarn. The volcanic metamorphicskarn is composed of garnets which are mainly grossularite and pyroxenes which aremainly diopside formed in a reductive environment. The hydrothermal metasomaticskarn is composed of garnets which are mainly andradite and pyroxenes which aremainly diopside formed in an oxidizing environment. The skarn formed in the two periods have similar total REE content rangingfrom141.331×10^-6to181.076×10^-6to that of the volcanic rocks in the stratum from157.63×10^-6to161.89×10^-6, with similar distribution patterns. The abovecharacteristics indicate the skarn in Dunde iron deposit might have resulted fromthermal metamorphim and hydrothermal metasomatism. Iron ore and the skarnspatially coexisted and experienced similar development and evolution.