A damped Lyα system along two lines of sight at z=0.93

He0512-3329 is a gravitationally-lensed double QSO with damped Lyα systems observed at z=0.931 in front of both QSO images (dla a and b). We have obtained spatially resolved HST STIS and optical VLT UVES spectra of both QSOs in order to study differences in the metal abundances across the lines of sight. We detect substantial differences, of roughly 0.5 dex, in both [mn/h] and [fe/h], on a transverse scale of 5 h^-1 kpc. Differential dust depletion appears as the most plausible explanation.