U-Pb dating of zircon and cassiterite from the Early Cretaceous Jiaojiguan iron-tin polymetallic deposit, implications for magmatism and metallogeny of the Tengchong area, western Yunnan, China

摘要

The newly discovered Jiaojiguan deposit, a medium-scale skarn iron-tin polymetallic deposit on the Sino-Burma boundary of Yunnan Province (SW China), is spatially associated with the biotite monzonitic granite. Here, we report new in situ zircon LA-MC-ICP-MS U-Pb ages, trace element and Hf isotope data from the granite, and U-Pb dating ages of cassiterite from the ore bodies. In this study, we obtain a weighted mean Pb-206/U-238 age of 124.1 +/- 1.4 Ma for the zircon and a Pb-207/Pb-206-U-238/Pb-206 intercept age of 123.8 +/- 2.2 Ma for the cassiterite. The granite crystallized during the Early Cretaceous, with zircons exhibiting epsilon(Hf)(t) values from -5.8 to -0.6 and two-stage Hf model ages (T-DM2) of 1.21-1.54 Ga. The close temporal and spatial links between pluton emplacement and ore-forming events suggest that magmatic-hydrothermal events were the key factors that triggered the genesis of the iron-tin polymetallic deposits in the area. Regional geochronological data show that tin mineralization took place three times during the Cretaceous-Palaeogene in the Tengchong block due to re-melting of the underlying supposed Proterozoic (1.5 +/- 0.5 Ga) Sn-rich strata/materials. Compared with those in the Bangong-Nujiang metallogenic belt (BNMB), we propose that the Cretaceous iron-tin polymetallic mineralization events in Tengchong-Baoshan closely resemble those of the Bangong-Nujiang belt in northern Tibet, both of which have experienced similar tectono-magmatic-metallogenic histories since the Mesozoic.