Petrogenesis of Scheelite-Bearing Albitite as an Indicator for the Formation of a World-Class Scheelite Skarn Deposit: A Case Study of the Zhuxi Tungsten Deposit

Abstract

Abstract Scheelite-bearing albitite is present in the form of rare, highly fractionated felsic dikes in the world-class Zhuxi tungsten deposit. Morphologically, the Zhuxi albitite forms individual dikes with thicknesses from 0.01 to 5.1 m in the orebodies. Additionally, the Zhuxi albitite is characterized by high sodium concentrations (Na2O = 6.08–8.04 wt %), low silicon (SiO2 = 56.81–62.56 wt %) and potassium concentrations (K2O = 1.44–2.62 wt %), and increasing P2O5 (0.1–0.7 wt %), Y (2.72–8.62 ppm), and rare earth element (8.28–28.89 ppm) concentrations from the tops to the bottoms of the dikes, which are controlled by the heterogeneous distribution of apatite grains in the albitite. The trace element geochemical characteristics and Sr-Nd isotope compositions of the albitite and the geochemistry of plagioclase, muscovite, apatite, and scheelite that formed in both the albitite and ore-related (altered) granites strongly suggest a genetic relationship between the two rocks. Given our new data and previous experimental data, as well as natural examples from around the world, we propose that the Zhuxi albitite is the product of a silicate-poor, H2O-rich melt that formed by melt–melt-liquid immiscibility processes in an extremely fractionated residual magma. A deep-seated (>3 kbar) granitic magma reservoir was directly related to the formation of these rare scheelite-bearing albitite dikes. Albitite dikes are the product of extreme fractionation of a granitic magma, and W is highly incompatible during magma evolution regardless of oxygen fugacity; therefore, intense tungsten mineralization development within albitite dikes should serve as an important criterion for judging the tungsten metallogenic potential.