The formation of the world-class Zhuxi scheelite skarn deposit: Implications from the petrogenesis of scheelite-bearing anorthosite
Abstract A quartz-free scheelite-bearing fine- to medium-grained anorthosite occurs as a dike in the world-class Zhuxi scheelite skarn deposit of South China. The anorthosite mainly comprises An-rich plagioclase (An avg = 91, ~90 vol%) + scheelite (~3 vol%) + apatite (~2.5 vol%) + ilmenite (~1.5 vol%) + titanite (~1 vol%), as well as minor (~2 vol%) fluorite, prehnite, chalcopyrite, pyrrhotite, pyrite, sphalerite, rutile, and uraninite. This paper reports the first occurrence of scheelite-bearing anorthosite of hydrothermal origin in a W deposit. Field, textural, mineralogical, and geochemical evidence suggest a hydrothermal genesis for the scheelite-bearing anorthosite in the Zhuxi deposit. The scheelite-bearing anorthosite formed when the Al-, Si-, P-, W-, and F-rich residual magma (fluid) was contaminated by pure limestone in a reducing environment. The formation of the scheelite-bearing anorthosite requires fertile (W-rich) metasedimentary rocks as a magmatic source, which formed granitic magma emplaced at a great depth that emanated W-enriched magmatic hydrothermal fluids during the latest stage of magma crystallization, thus producing the large-scale tungsten mineralization in the Zhuxi mine.