It's the GOG release of Far Cry (1.4).
No problem with a GeForce 750 and lastest drivers.
Problems with a Radeon 7850 and lastest Crimson, zooming in with the sniper rifle:
It seems some kind of LoD-related cubemap/normalmap problem.
Using FCAM mod:
*first level zoom (correct rendering)
*second level zoom (wrong rendering, the sand texture is overridden by other maps)