Oligocene Nb-Ta-W-mineralization related to the Xiaruleucogranite in the Himalayan Orogen

Himalayan leucogranites are abundant within a ~2000-km-long, E-W trending belt on the Tibetan Plateau. Recently, it has been shown that several and pegmatites (including aplites) of Himalayan leucogranitic closely related to rare-metal mineralization. The commonly peraluminous strongly peraluminous, classifying as highly-fractionated granites in terms whole-rock geochemistry characteristic mineral assemblage with phases such garnet, mica, zircon oxides. contain typical rare-metal-bearing minerals formed during magmatic-hydrothermal stage, including spodumene, beryl, columbite-group (CGMs), cassiterite, wolframite, associated Li-, Be-, Nb-Ta-, Sn- W-mineralization. Multiple episodes magmatism mineralization (~25−12 Ma) have identified for leucogranites. Nevertheless, our understanding orogeny its age range remains limited. Xiaru Dome, which crops out central part northern Himalaya, is mainly composed middle-high grade metasedimentary rocks granitic gneiss. Intrusions tourmaline-garnet-bearing leucogranite Be-Nb-Ta pegmatite relatively common. Beryl CGMs previously observed total Nb2O5 Ta2O5 contents up ~0.014wt%. During recent field work, Nb-Ta-W-bearing tourmaline granite/pegmatite was found first time. To further constrain evolution Nb-Ta-W mineralization, we studied rock-forming ore-forming leucogranite/pegmatite country rock We characterized geochemical compositions, textures chemical compositions oxide minerals, complemented these by U-(Th-)Pb dating CGMs, monazite. Our work shows samples (ACNK =1.06−1.26), high silica (SiO2 = 72.2wt%−75.5wt%) alkali (Na2O+ K2O 8.4wt%−9.4wt%). They concentrations B, Nb, Ta W (780×10−6, 58×10−6, 17×10−6 67×10−6, respectively), hosted schorl, wolframoixiolite, qitianlingite, wolframite. Zircon monazite at ~530−387, ~44, ~36−35 Ma, indicating multiple intrusions, while U-Pb reveals Nb-Ta occurred exclusively ~34−33 Ma. Oligocene district thus oldest (earliest) ever discovered. highlight best determined ore-minerals directly instead or conclude B concentration parental magma possibly permitted fractionation Nb Ta. Magmatic columbite early, later metasomatically altered Ca-W-F-rich fluids. At hydrothermal formed, scheelite, microlite. enrichment local gneiss, located adjacent granite, ingression W-bearing fluids from leucogranite. Compared skarn-type Cuonadong pluton eastern orogen, there least two types leucogranites: Skarn-type granite-type. discovery gneiss dome deepens provides basis exploration similar elsewhere Orogen.