Mountains need to be a certain height and size to have silver. A stone golem is a good indicator there is silver around.

Swamps need to be a certain size. The long strips that are not wide will often not have crypts at all.

Well that is how it used to be before H&H I really don't know at this point. I used to explore to make sure stuff was there before I started building a logistical base but that may be too dangerous at this point... IDK.