矿床地球化学国家重点实验室知识库

The Xuebaoding deposit in the Songpan–Garzê orogenic belt, western China, spatially associated with the Xuebaoding granitic complex, is a unique pegmatite-type Sn–W–Be deposit within the giant Songpan–Garzê polymetallic belt. A lack of precise geochronological constraints on the timing of mineralization for this deposit has precluded definitive statements relating to a genetic link between ore formation and granitoid intrusion, up to now. To address the temporal relationship between the emplacement of granite and the spatially associated Sn–W–Be polymetallic mineralization in the Xuebaoding deposit, systematic cassiterite U–Pb and muscovite Ar–Ar dating were undertaken. U–Pb data of cassiterite analyzed by In-situ LA-MC-ICP-MS provided an isochron age of 193.6 ± 6 Ma (at 95% confidence level, MSWD = 4). The ⁴⁰Ar/³⁹Ar dating on the muscovite intergrown with the cassiterite sample yielded a plateau age of 194.50 ± 1.02 Ma (MSWD = 1.26), and an inverse isochron age of 194.53 ± 1.05 Ma (MSWD = 1.34). Both the Ar–Ar dates overlap the U–Pb date within uncertainties, placing the timing of tin mineralization at ~ 193–194 Ma. This is consistent with field geological relationships that show veins cutting marble and granite, and with previous Sm–Nd dating, within experimental error, for scheelite and indicates that Sn–W polymetallic mineralization at the Xuebaoding deposit occurred during the Early Jurassic.

Combined with previous published trace element and REE data from the Xuebaoding granites and other ore minerals, as well as the timing of granite emplacement, the temporal and genetic associations between granite intrusion events and Sn–W mineralization of this deposit have been discussed in this paper. The results suggest that the Pankou granite is genetically related to the polymetallic mineralization in Xuebaoding Sn–W–Be deposit, and further demonstrate that the latest-phase of granitic intrusion is commonly favorable for Sn and/or W mineralization. Although the Pukou granite also exhibits close relationships with the ore formation in its spatial distribution and element characteristics, the possibility as a parent for this deposit is excluded duo to the time span from its emplacement to mineralization event that exceed the estimated life of modern geothermal systems (< 1–2 Ma). The constraints on the timing of mineralization and for the element and fluid source provide important insight into the genesis of the Xuebaoding deposit.