The WB beeps so you need sound on. It beeps faster and faster as you get near, until its pretty darn fast and then you dig around a bit.
silver is a long, twisted tube formation in this game, and it occasionally juts out of the ground so you can just see it. It looks like a dark rock. Usually it is buried and you need to WB find to dig to it then it mines much like copper.
There are mountains without, but normally HIGH mountains with drakes will have some. No drakes, often, no silver.