Study on internal characteristics and mineral inclusions of zircons from the Daixian rutile deposit, Shanxi and its geological implication

Combined with petrographic observations and mineral compositions, morphologies, inner structures and mineral inclusions in zircons of ores from the Hongtang rutile deposit of Daixian, Shanxi. The zircons are subdivided into complicated zircons with core, mantle and rim and single zircons without overgrowth based on their relative locations, morphologies, CL images, SHRIMP ages and mineral inclusions. Type I zircons are considered as inherited zircons, with rounded shape and no obvious zoning, which contain enstatite and phlogopite, showing different mineral association from that of its host rock. They are inferred to be previous minerals preserved in zircons before the formation of its host rock, and likely derived from mantle. Type II zircons have broad and clear zoning, and contain anthophyllite and hedenbergite ( ? ), in accordance with mineral associations of the host rock. They are speculated to be high grade metamorphic zircons. Type III zircons are mainly rimed and speculated to be fluid-related zircons. Type IV zircons are mostly euhedral, with low-luminescence of CL and narrow growth zoning. They have albite, quartz and muscovite mineral inclusions, corresponding to middle-pressure green-schist facies. Type IV and type III zircons might form in coeval thermal event. Combined with petrographic study results, it is inferred that the parent rock of this rutile ore deposit may be magmatic rock, and experience at least two thermal events, the earlier ones may result in the reset of system U-Th-Pb in zircons. The results of this investigation also show that study and analysis of mineral inclusions in zircons of high grade metamorphic rocks are an effective means of discussing the genesis and subsequent geological events of the host rock.