Discriminating hydrothermal fluid sources using tourmaline boron isotopes: Example from Bailingshan Fe deposit in the Eastern Tianshan, NW China

摘要

Tourmaline is an important B-bearing mineral in many types of hydrothermal deposits, and its chemical and boron isotopic signatures shed light on the nature and evolution of the metallogenic processes. Two generations of hydrothermal tourmaline in potassic-altered rocks (tourmaline I) and subsequent veinlets (tourmaline II) have been identified at the volcanic-hosted Bailingshan Fe deposit in the Chinese Eastern Tianshan, NW China. Both tourmaline I and II have low Ca contents and X-site occupancy, and belong to the alkali group. Tourmaline I grains plot in the schorl field or between the dravite and schorl fields, whereas tourmaline II grains are largely Mg-rich dravitic. Mineral textural and geochemical features suggest that the compositions of tourmaline I and II were mainly controlled by the host rock and hydrothermal fluid compositions, respectively.