Abstract:

Located in Taxkorgan area of western Kunlun Mountains, the largescale Kalaizi BaFe deposit is hosted in the metamorphic volcanic sedimentary sequences of previously defined “Bulunkuole Group”. As a unique BaFe deposit in western Kunlun Mountains, the ore minerals mainly consist of magnetite and barite, and the ores are characterized by banded or laminated structure. While the wallrocks consist predominantly of metaargillaceous clastic rock (garnetbearing twomica quartz schist), which is interlayered with magnetitebarite ore, and a small amount of metaacid volcanic rocks (biotite plagiogneiss and biotite plagioclase granulite). LAICPMS zircon UPb dating age of biotite plagiogneiss limits the oreforming age of the Kalaizi BaFe deposit to ca. 537.2±6.4 Ma, which also suggests that the previously defined “Bulunkuole Group” can isolate the Cambrian volcanosedimentary metallogenic series. Oxygen isotope compositions of magnetite samples, sulfur isotope compositions of sulfate minerals and pyrite show that the ore deposit was marine hydrothermalexhalation sedimentary type deposit (SEDEX) that was affected by bacterial sulfate reduction. So the specific mineralization mechanism may be as follows: in the Early Cambrian semirestricted marine basin, when barium and ironbearing hydrothermal fluids were migrated and encountered with sea water by fault, the minerals precipitated because of the changes in temperature, pH and oxygen fugacity. To summarize, barite formed by mixing of bariumbearing hydrothermal fluids and sulfatebearing pore waters. Pyrite precipitated where ironbearing hydrothermal fluids encountered pore waters that had been charged with H2S by bacterial sulfate reduction. And after the H2S was consumed, magnetite precipitated directly by suboxic ironbearing hydrothermal fluids in the sea floor.

Key words: barite, magnetite, zircon U Pb dating, sulfur and oxygen isotopes, Kalaizi Ba Fe deposit, Western Kunlun Mountains