A Miocene tungsten mineralization and its implications in the western Bangong-Nujiang metallogenic belt: Constraints from U-Pb, Ar-Ar, and Re-Os geochronology of the Jiaoxi tungsten deposit, Tibet, China

摘要

The Jiaoxi quartz-vein type wolframite deposit is the first tungsten mineralization discovered in the western part of the Bangong-Nujiang metallogenic belt, which is well-known for the porphyry-epithermal-skarn Cu-Au mineralization. The Jiaoxi deposit is associated with a porphyritic monzogranite that intrudes sandstone and shale in the Shiquanhe ophiolite melange. The ages of the magmatism and mineralization in the deposit are here constrained by the dates obtained from the porphyritic monzogranite, hydrothermal muscovite and molybdenite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating of two porphyritic monzogranite samples yields weighted mean Pb-206/U-238 coincident age of 14 +/- 1 Ma. Two samples of hydrothermal muscovite from wolframite-bearing quartz veins yield plateau Ar-40/Ar-39 ages of 13.4 +/- 0.1 and 13.3 +/- 0.1 Ma, respectively. Re-Os model ages of five molybdenite samples range from 11.4 +/- 0.2 to 11.8 +/- 0.2 Ma, with a weighted mean model age of 11.6 +/- 0.2 Ma. These dates indicate that the tungsten mineralization at Jiaoxi was formed during the Middle Miocene. This Miocene tungsten mineralization is significantly different from the Early and Late Cretaceous Cu-Au mineralization in the western part of the Bangong-Nujiang metallogenic belt. Our dating results show that there is a Middle Miocene tungsten mineralization in the western part of the Bangong-Nujiang metallogenic belt. The tectonic setting for the tungsten mineralization is here interpreted to be the regional extension associated with the India-Asia continental collision. The discovery of the Jiaoxi deposit has important significance on regional tungsten prospecting.