Characteristics and Geological Significance of Late Miocene Skarn-Type Tungsten Mineralization in Ramba, Southern Tibet

The Ramba leucogranite, located in the eastern part of the Northern Himalaya, is mainly composed of two-mica granite. The amphibolite in contact with it is commonly skarnized and accompanied by scheelite mineralization. To qualify the diagenetic and metallogenic ages and the ore-forming fluid characters, an integrated approach involving zircon U-Pb and mica Ar-Ar dating, and mineral geochemistry was carried out. The Ar-Ar age (6.3 Ma) of muscovite from the scheelite-bearing quartz vein yielded is comparable to the zircon U-Pb age (7.3 Ma) of two-mica granite, indicating that the granite emplacement and associated tungsten mineralization both occurred in the Late Miocene, which is the youngest known rare-metal mineralization event in the region. The iron ratios of garnet and pyroxene mineral pairs within the scheelite-bearing skarn (3.12 to 3.74), and the relatively low Mo content (12.0×10-6-56.8×10-6) of scheelite, collectively indicate that the ore-forming fluid is reduced, which is consistent with the magmatic zircon oxygen fugacity calculated results (ΔFMQ=-5.78 to -2.08). The rare-earth element characteristics of scheelite are inherited from the leucogranite granite, further indicating that the W-rich ore-forming fluid was dissolved from the evolved granitic melt and subsequently reacted with the Ca-rich wall rocks to induce the precipitation of scheelite. This study reveals that the contact metamorphic zone between Himalayan leucogranite and surrounding wall rock is a favorable site for rare-metals, and deserves attention in future prospecting. © 2024 China University of Geosciences. All rights reserved.