I first gave it a basecoat of Citadel Texture: Armageddon Dust. Once the paint was dry, I drybrushed with Citadel Layer: Ushabti Bone and then used some Citadel Mordheim Turf.
What I did note was that it didn’t quite cover the coin as well as I thought it would. So for my other Foundry models I decided to use a bit of green stuff to texture the base.
This will combined with the Citadel Texture make the base look more like a base and less like a coin.