Molybdenite Re-Os Isotopic Dating of Xitian Deposit in Hunan Province and Its Geological Significance

The Xitian large-scale W-Sn polymetallic ore field has been explored in recent years. It is found in jointed adjoining areas of the Nanling and Qinhang metallogenic belts which are located on the boundary between Hunan and Jiangxi provinces, and the junction of the Yangtze and Cathaysia blocks. At present, there are several debates about the formation ages of the ore bodies and nearby granitic intrusions. For example, is W-Sn mineralization related to either Indosinian or Yanshanian granites? Were numerous different types of ore bodies formed in the corresponding period? The separation of molybdenite minerals from two tin polymetallic deposits, Shantian greisen-quartz vein ore deposit and Tongmushan crushed zone-alterated rock ore deposit was undertaken and is reported in this paper. Re-Os model ages of molybdenite in these two deposits yielded (158.9±2.2) Ma (2SD) and (160.2±3.2) Ma (2SD), respectively, which show they were generated in the early stage of the late Jurassic period. According to statistical data of mica Ar-Ar and molybdenite Re-Os ages, Longshang, Heshuxia, Shantian and Tongmushan ore deposits were all formed during 150-160 Ma, which is the peak period of W-Sn large-scale mineralization related to granitic intrusions. Rhenium contents of the two molybdenite samples are 12.44×10^-6 and 2.367×10^-6, respectively, which suggests that metallogenic materials were derived from crustal-mantle mixture and crust. Combining with ninety data of rhenium contents in molybdenites of W-Sn polymetallic deposits closely related to granitoids in Nanling area in late Jurassic, the suggestion that a majority of metallogenic materials were derived from crust is given, with only a few of them derived from crust-mantle mixture.