Halogens in hydrothermal sphalerite record origin of ore-forming fluids

The halogens Cl and Br are sensitive indicators for the origin of ore-forming fluids. Here, we use a combination of microchemical and microscopic methods to show that measurable concentrations of these elements commonly occur as atomic-scale substitutions within hydrothermal sphalerite. Furthermore, the Cl/Br ratios of the halogen-rich sphalerites investigated in this study are indistinguishable from those of the corresponding ore fluids. Thus, they record fluid compositions, which are in turn closely related to fluid origin. Given the abundance of sphalerite in hydrothermal base-metal deposits, as well as the relative ease of conducting in-situ microchemical analyses, the halogen signature of sphalerite has the potential to become a sensitive proxy to distinguish between different ore-forming environments.