Mineralogical characteristics of tourmaline in the Houxianyu boron deposit in Liaoning and their significance for rock and ore formation

Abstract：The mineralogical and chemical characteristics of tourmaline in the Houxianyu boron deposit, Liaoning, are analyzed and their significance for the formation of rocks and deposits is discussed. The tourmaline in the study area belongs to the magnesium tourmaline-iron tourmaline series (schorl-dravite solid solution series) and its Mg/Fe has close spatial and temporal relations to borate orebodies. Tourmalines with different modes of occurrence show marked differences in color, size, shape and zonal features. The content of Mg is quite high in all zones of tourmaline near the borate orebodies and has a general trend of decrease from the center to edges, whereas the iron content is quite high in all zones of tourmaline far away from the borate orebodies and has a general trend of decrease from the center to edges. The tourmaline content is generally higher in the hanging wall than in the footwall. Tourmalinite mainly appears near borate orebodies and there is a pronounced positive correlation between Mg/Fe and Na2O in tourmalines far from the borate orebodies. The above-mentioned chemical characteristics of tourmaline reflect the features of the evolution of fluids during the formation of rocks and deposits. The older tourmalines formed by metasomatism of the boron-rich part in sediments. During the evolution of the evaporite basin, the contents of Mg, Na and K in fluids increased, which induced zoning of Mg/Fe. All the mineralogical and chemical characteristics of tourmaline indicate that tourmalines are of metamorphosed sedimentary origin and hydrothermal metasomatic origin and that the formation of tourmalines is closely related to the deposition of borate.