There are different tiers of ores in Terraria, each with its own set of ore types. The tiers determine the rarity and strength of the ores.

Here’s the key point: each tier of ore can be either the classic or the alternative variant, but the three tiers (pre-hardmode, hardmode, and post-Lunar Event) are independent of each other. This means that in a single world, you can have Copper (classic) alongside Tungsten (alternative), or Iron (classic) alongside Platinum (alternative).