Copper Ore

Every new character spawns holding copper tools whether or not the world generated any copper, so the ore is not what gets you moving. What it buys is a small step up from wood and cactus gear, and that step vanishes the moment you hit a silver or gold vein. If you are pushing toward the first boss, mine what you trip over and skip the armor entirely. Slimes cough up the occasional piece as a bonus drop, so a modest stack tends to accumulate without any effort on your part.

A world rolls one of the two at generation. It changes nothing about how you play. The tin recipes line up one for one against these, the gear sits at the same point in progression, and both are stepping stones you leave behind quickly. Nothing in a copper world is gated behind having tin instead.