Surface chemistry of weathered zircons

We have investigated the surface morphology and chemistry of zircon in sediments and soils of the Amazon basin (Brazil). The extent of metamictization in the near-surface region of these zircons was previously determined by Raman micro-probe. Scanning electron microscopy (SEM) reveals scarce dissolution features and numerous marks related to the sedimentary transport of the zircon grains, which attest to the high resistance of these zircons to tropical weathering. Rutherford backscattering (RBS) micro-analysis and X-ray photoelectron spectroscopy (XPS) failed to reveal any strong chemical change at the surface of the zircon grains. In particular no Zr enrichment was detected, which excludes the occurrence of a protecting layer of Zr oxide or hydroxide at the zircon surface. This result suggests that the slow weathering rate of zircon could be the principal factor limiting the Zr mobility in the investigated weathering environments.