Multistage in situ fractional crystallization of magma produced a unique rare metal enriched quartz-zinnwaldite-topaz rock

Abstract

Highly fractionated granites and pegmatites have special petrogenesis and potential economic significance due to the enrichment of incompatible elements (Li, Rb, Cs, etc.) and flux elements (F, B, Li, etc.) in the magmatic volatile phase (MVP). Here we decipher the origin of the giant Zhengchong Rb-dominated deposit associated with highly fractionated A-type granite in South China. An extreme fractional crystallization (up to 98.3%) was required to generate super enrichment of incompatible elements and flux elements by the model of single-step in situ crystallization. An alternative model incorporates episodic remobilization and multistage in situ crystallization of a long-lived mush. The MVP and incompatible elements migrate via reactive flow at intermediate degree of crystallization (70–80%) in each intrusion fits with the observed geochronological and geochemistry data. This geochemical model can help us understand the evolution of magma reservoirs and the concept of magmatic distillation columns.