Petrogenesis of Shihuiyao Rare-Metal Granites in the Southern Great Xing'an Range, NE China

Shihuiyao Rb-Nb-Ta-rich granites from the Late Jurassic period are newly discovered rare-metal-bearing granites found in the southern Great Xing'an Range, NE China. Further research of these granites may contribute to better understanding the petrogenesis of rare-metal granites and their associated mineralization mechanisms. The granites are high-silica (SiO2 = 73.66-77.08 wt%), alkali-rich (K2O + Na2O = 8.18-9.49 wt%) and weakly to mildly peraluminous with A/CNK values (molar ratios of Al2O3/(CaO + Na2O + K2O)) ranging from 1.06 to 1.16. High differentiation indexes (DI = 95-97) and low P2O5 contents demonstrate that Shihuiyao rocks are low-P and peraluminous rare-metal granites. Mineral chemistry and whole-rock geochemistry can be used to obtain the following lithological sequence: zinnwaldite granite, muscovite-zinnwaldite granite, amazonite-bearing granite and amazonite pegmatite. The effect of the rare-earth element tetrad; low K/Rb (18.98-32.82), Nb/Ta (2.41-4.64) and Zr/Hf (5.99-8.80) ratios; and the occurrence of snowball-textured quartz suggest that extreme magmatic fractionation might be the key factor that causes Rb-Nb-Ta enrichment.