Geochemistry of hydrothermal tourmaline from IOCG occurrences in the Great Bear magmatic zone: Implications for fluid source(s) and fluid composition evolution

摘要

Tourmaline crystallized during iron oxide and alkali-calcic alteration and IOCG mineralization in the Great Bear magmatic zone, Canada. Within the samples analyzed, tourmaline occurs as small crystals in the groundmass of hydrothermal breccias (Southern Breccia and Contact Lake), or as large prismatic crystals in quartz (+/- oremineralogy) veins (Contact Lake, DeVries Lake, and NICO). The tourmaline from these localities is predominantly shorlitic in composition, with minor dravitic, uvitic and feruvitic components. The boron isotopic composition ranges from -15 parts per thousand to -5 parts per thousand, with the majority of values between -15 parts per thousand and -10 parts per thousand. The lack of variation among samples supports a common fluid source across the belt for the metasomatic-hydrothermal systems. These results are isotopically similar to global magmatic and non-marine evaporitic reservoirs, and lighter than seawater and marine sedimentary rocks. The delta B-11 results support a single-fluid IOCG deposit model for the systems studied, wherein metasomatic-hydrothermal fluids derived by magmatism ascend and evolve over time through fluid-rock interactions.