Advection-Diffusion Controlled Lithium Isotopic Distribution in Contact Aureoles: A Case Study from the Florence County Pegmatites, Wisconsin

Abstract

Stable isotopes are useful tracers of fluid-rock interactions in contact aureole settings. To date, only a few case studies have used Li isotopes to study fluid-rock interactions in contact aureole settings. These studies highlight the very large Li isotopic fractionation that can be generated in these settings via diffusion of Li from the pluton into the country rocks, but none of these studies have generated a complete and detailed section of the contact aureole needed to understand the Li distributions. Here, I report the results from a combination of Li isotope analyses and 2-D advection-diffusion modeling for two detailed profiles through country rocks adjacent to Li-rich pegmatite dikes in the Florence County pegmatite field. The results show that the Li concentration and isotopic distribution in the two contact profiles is consistent with fluid infiltration and diffusion of Li through a grain boundary fluid from the pegmatites into their country rocks.