Altitudes and locations for mining

What are the best altitudes and locations to mine at for metals and and gems?

Here’s a simple rundown:
Iron/copper 0-100+
Silver 0-30
Gold 0-20
Diamond/ruby 0-30
Sapphire/topaz 100+ (215 was a good alt)
Emerald/amethyst 0-30 (watch for lava)
Tech device and fossils are usually high alt

For all the stuff that spawns low, as listed in previous posts, one thing I try to do is to keep to around alt 16-18. 16 seems to be the altitude of the surface of lava pools underground very often.