Deformation, metamorphism and mineralization of the Mengku iron deposit, Altay, Xinjiang

The Mengku iron deposit, located in south margin of Altay orogenic belt, occurs in metamorphosed volcanic sedimentary rocks of the Lower Kangbutiebao Subgroup of Lower Devonian age. The ore bodies of the deposit are controlled by the Tiemuxiaergun syncline within the Kangbutiebao Group. Our study shows that the deposit has experienced three mineralizing periods, which are marine volcanic sedimentary mineralizing period, regional metamorphic mineralizing period and hydrothermal metasomatic mineralizing period. Regional metamorphic mineralizing period includes disseminated-banded magnetite stage and massive magnetite stage. Hydrothermal metasomatic mineralizing period includes calc-silicate metasomatism stage, sulfide stage and calcite-quartz vein stage. Among them, regional metamorphic mineralizing period is the most important one, with banded or massive magnetite formed by pressure-solution and enrichment. Skarn-like rocks were generated by metasomatic hydrothermal fluid flowing through silicon-rich and calcium-rich rocks and posterior to the formation of massive magnetite. The later copper mineralization was a hydrothermal metasomatic mineralizing event Homogenization temperatures of primary fluid inclusions in metamorphic layer quartz veins (Q(2)) are 235 similar to 511 degrees C, and those of secondary are 157 similar to 326 degrees C for lateral fluid inclusions. Homogenization temperature of fluid inclusions in the later quartz veins (Q(3)) varies between 122 similar to 337 degrees C. We got trapping pressures of coexisting pure CO2 and H2O-NaCl fluid inclusions in Q, by isochore crossing method, which are 73 similar to 90MPa. The oxygen isotope data on magnetite show a range of -2 parts per thousand similar to +1. 28 parts per thousand in delta O-18(SMOW) with the average of -0. 15 parts per thousand, which is similar to those of volcanic sedimentary-metamorphic iron deposits in other areas. Decrepitate curves of magnetite also clearly shows the features of multi-stage metamorphism superimposing. It could be presumed that the Mengku iron deposit was finally formed by enrichment of regional metamorphism and hydrothermal metasomatism during Altay Orogeny.