The Characteristics And Genetic Of Kaladawan Area Iron Deposit, Altyn Tagh, Xinjiang

Kaladawan area iron deposit is located in the central of Hongliugou-Lapeiquan Ordovician rift zone which lies in the mid-eastern of Altyn Tagh, northern Tibet Plateau. It is one of the largest iron deposits in this area, which has been discovered in the recent years. But the genesis of Kaladawan area iron deposit is still in debate.Based on the detailed field geological investigation, the systematic sample collection and the predecessors research work, the characteristics and geochemical features of the deposits has been carried out, the genesis of Kaladawan area iron deposit is clarified in this paper.Through three years study, we make some brief achievements as follows:Kadawan area iron deposit which belongs to Zhuoabulake Group is developed in the volcanic-sedimentary rocks, in the Upper Cambrian lithology. The orebodies is mainly hosted in the volcanic rock with some being in marble, and it is stratabound property. Most of the magnetites in deposit are mid-fine grained, but some are coarse grained magnetite. Coarse grained magnetite is probable to be the recrystallization from the mid-fine grained magnetite. Siltstone and magnetite-bearing intermediate-basic volcanic rock are imbedded under the microscope. The mineral compositions of magnetite imply the magnetite of the Kaladawan area iron deposit belong to volcanic-sedimentary magnetite. So, the Kaladawan area iron deposit is a type of volcanic-sedimentation-related deposit.Skarn in the Kaladawan area iron deposit is fairly developed, and skarn mineral assemblages are composed of garnet, pyroxene, chlorite, epidote. actinolite, tremolite. While, the distribution of skarn in the Kaladawan area iron deposit is different with general skarn deposit. Skarns in the Kaladawan area iron deposit aren’t controlled by the contact of acid-intermediate intrusive rock with carbonate rock. Acid-intermediate intrusive rocks in the Kaladawan area iron deposit have no obvious wall rock alteration. Magnetite and the skarn minerals are mainly symbiotic under the microscope and the end member of garnet is mainly andradite, suggesting that the Kaladawan area iron deposit is probably affected by magmic hydrothermal fluid.Zircon is collected from the intermediate to basic volcanic rocks in the volcanic-sedimentary rocks in Kladawan area. The result shows the age of zircon SHRIMP U-Pb dating is at517Ma, representing the mineralization ages of iron deposit. By analysizing the geochemical of basalt in and out of iron deposit, suggesting the iron deposit might be formed in an island arc environment.The REE distribution patterns of skarn, iron ore and magnetite are obvious divided into two part:one part is slight rich light REE and the other part is rich light REE, this character may imply that skarn, iron ore and magnetite were affected by the different kind of fluid activity.The Y/Ho ratio of skarn in Kaladawan area iron deposit, ranges from28.45to 52.87(average36.45). The Y/Ho ratio of iron ore in the Kaladawan area iron deposit ranges from29.74to36.79(average33.26). They have similarly Y/Ho rate, suggesting that they are affected by the similar fluid activity. Acid-intermediate intrusive rock in the south of the Kaladawan area iron deposit, skarn and iron ore show a significant correlation in Y/Ho-La/Ho, Sm/Nd-LREE/HREE and Sm/Nd-Td/La diagram, suggesting skarnization of the Kaladawan iron deposit is resulted from the acid-intermediate intrusive rock in the south of the Kaladawan area iron deposit.Zircon is collected fron the three samplies of granitic intrusion rock in the Kaladawan area iron deposit, The result shows the age of zircon SHRIMP U-Pb dating of the three samplies is at477Ma,479Ma,488Ma, Re-Os isotopic dating of the molybdenites obtain an isochron age of480.2±3.2Ma, which was consistent with the emplacing age of the granitic intrusion in Kaladawan iron deposit. These features indicated that the molybdenites were results of the magma fluid activity. Meanwhile.480.2±3.2Ma represent the age of skamization of iron deposit.In summary, Kaladawan iron deposit is classified as a volcanic-sedimentary types iron deposit, which is latter effected by the skarnization.