My thinking is that in an atmosphere rich in hot sulfuric acid they couldn't stand a chance. Although I am unsure of what exactly would be going on chemically at the interface between the venerean litho and atmo spheres.
As best as I can understand from these papers, it would seem that the precise levels are not known, but that noticeable weathering on Venus implies significant(?) levels of oxidation on the surface. The papers primarily address the oxidation of Fe (iron) mineral on the surface.
Most of the material in the papers is derived from modeling of the surface and atmospheric interactions from what little data we have, as well as spectroscopy and other observations of the character of the surface material.