Boron isotope systematics of tourmaline formation in the Sullivan Pb-Zn-Agdeposit, British Columbia, Canada

We report here the results of 54 boron isotope analyses of tourmaline assoc iated with the giant Sullivan Pb-Zn-Ag deposit in southeastern British Colu mbia, Canada. The delta(11)B values range from - 11.1 to - 2.9 parts per th ousand, which is almost as great as the range found worldwide in tourmaline s from 33 massive sulfide deposits and tourmalinites in dominantly elastic metasedimentary terranes. The major control on the overall delta(11)B value s of the Sullivan tourmalinites is the boron source. Potential controls ove r the large range of the data also include: (1) differences in formation te mperatures of the tourmalinites, (2) different stages of tourmaline formati on, (3) variations in the proportions of dissolved boron incorporated into the tourmaline (Rayleigh fractionation), (4) seawater entrainment, and (5) post-depositional metamorphism. The boron isotope data at Sullivan are cons istent with boron derivation from leaching of footwall elastic sediments. H owever, the great abundance of tourmaline in the Sullivan deposit suggests that the local elastic sediments were not the sole source of boron, and we argue that non-marine evaporites, buried deep below the orebody, are the mo st viable source of this additional boron. It is likely that some of the va riation in tourmaline delta(11)B values reflect mixing of boron from these two sources. Comparison of the potential effects of these controls with geo logic and other geochemical evidence suggests that major causes for the wid e range of delta(11)B values measured at Sullivan are seawater entrainment and Rayleigh fractionation, although in places, post-depositional alteratio n and thermal metamorphism were important in determining delta(11)B values of some of the recrystallized tourmalinites. (C) 1999 Elsevier Science B.V. All rights reserved.