So I unlocked Growling Grotto today, and quickly started getting mithril ore. Great! But… I'm also still getting copper. I kinda feel like, at this point, copper is really unnecessary and just clogs up your cart. Actually, if you don't upgrade your cart, this means that you can lock yourself out of mining unless you drop some if you're unlucky since you're getting 4 ores (5 if you count moonstone, but that only takes one to smelt) that need 5 to melt, which just really rubs me the wrong way when the expansions cost moonstones. If I want copper, I'll go to Lucid Lagoon, it's faster and drops more of it. I'm not going to go all the way down to Growling Grotto, and presumably Fluorescent Fountain and The Deep Deep in the hopes of pulling out some copper or iron.
Edit: You can very rarely get Lorium here too. This single green boy is messing me up but it pains me to toss out rares.
So basically, I think at some point copper (and probably iron) should stop dropping from mining because it's just… excessive and really makes you feel the burden of cart space, especially if you haven't paid in premium currency for more. I joke a lot about this being wolf-based Minecraft, but it isn't. You stop needing these low level materials eventually and if you do need them because you want some iron armor or swords, you can just… go get them really easily. And even if it was Minecraft, you can only get certain ores at certain depths!
I was excited to unlock a new location, but now I'm just like, ugh, the deeper I go the less bars I can smelt at a time because of all this clutter.