GEOLOGY AND GENESIS OF DABAISHITOUGOU TITANIUM MAGNETITE DEPOSIT IN MIDDLE QILIAN MOUNTAINS

The Dabaishitougou area in the northern margin of Tuolai South Mountain in middle Qilian Mountains, tectonically located in the mid-Qilian magmatic arc belt, belongs to the Caledonian W, rare metals, Cu(Ti, Sb, Au) metallogenic belt. The titanium magnetite mineralized bodies, obviously controlled by lithology and characterized by multistage mineralization, are mainly occurred in the gneiss member of Palaeoproterozoic Tuolai Group and the schist and quartzite members of Moshigou Formation of Mesoproterozoic Huangzhong Group. With petrographic observation, electron probe microanalysis(EPMA) and artificial heavy concentrate analysis, it is determined that the titanium minerals are dominated by titanium magnetite with minor ilmenite and trace rutile. The source of titanium minerals is discussed based on the in-depth study of metallogenic characteristics and occurrence state of titanium magnetite deposit. It is considered that the mineralization is of volcanic exhalation-sedimentary type, proving that the ore-forming materials are most likely from Ti-rich basic-ultrabasic volcanic rocks brought by volcanic eruption formed after the early fractional crystallization and accumulation rather than from the pegmatite body. It is the first time that titanium magnetite bodies have been found in Dabaishitougou area of middle Qilian Mountains through verification of documents. Thus the study results can provide a theoretical basis for follow-up exploration.