Genesis of the recently discovered Daxiyingzi Rb–Be deposit on the northern margin of the North China Craton: Evidence from 40Ar/39Ar ages and geochemical data

Abstract

A new Rb–Be rare metal deposit has been discovered in the northern margin of the North China Craton in Fuxin City, western Liaoning Province, China. The Daxiyingzi Rb–Be deposit is a granitic pegmatite-type deposit and composed mainly of biotite granite, albite granite, and amazonite granitic pegmatite. Amazonite and beryl are the main ore minerals containing Rb and Be, and occur in the amazonite granitic pegmatite. We present integrated biotite 40Ar/39Ar geochronology, mineralogy, whole-rock geochemistry, and Nd–Pb isotope analyses of the Daxiyingzi ore-bearing granites to better understand their petrogenesis and geodynamic setting. Biotite separates in biotite granite and albite granite yield 40Ar/39Ar ages of 223.27 ± 2.39 and 223.37 ± 2.45 Ma, which we interpret as the metallogenic age of the deposit. The Daxiyingzi granites have high A/CNK ratios (1.01–1.11) and sufficient contents of SiO2 (74.68–79.42 wt%), total alkali (K2O + Na2O, 7.89–9.49 wt%), Li (64.0–300 ppm), Be (6.85–10.95 ppm), Nb (38.2–144 ppm), Ta (12.6–109 ppm), and Rb (60.8–1426 ppm). Depletion in Eu, Ba, Sr, P, and Ti and enrichment in Rb, Th, Nb, Ta, Nd, and Hf indicate that the granites are highly fractionated I-type granites. The Nd–Pb isotopic compositions [εNd(t) = −2.5 to −4.1; TDM2 = 1320–1202 Ma] of these granites suggest that they were derived from a single magma reservoir in an extensional orogenic setting at ∼223 Ma via high-temperature partial melting of Mesoproterozoic–Neoproterozoic basement and the injection of mantle derived magma. As a peraluminous magmatic polymetallic deposit formed in an orogenic setting, the Daxiyingzi Rb–Be deposit represents a potential new direction for prospecting along the northern margin of the North China Craton.