Simplest method that doesn't need adding extra "chunks or ore" intermediate items and only a minimum amount of changes. IMHO the best way to add such a suggestion with greatest odds of it being noticed/accepted.
- Ore Blocks are made up of a specific stone-type base (stone, granite, etc.) which is only a different damage value for a specific ore (defined by the block id).
- The ore only appears in normal stone types that make some sense, and never in any weird places.
Putting Overworld ores in other dimensions would open a can of worms. I'd also probably forget obsidian and sandstone.
Obsidian isn't spawned anyway, it results from water spreading over lava EVEN the obsidian from the initial world generation is actually obtained like this SOON AFTER the chunk is created, because at the game tick where the chunk gets generated, the waterfall is still only 1 water source yet without any flowing water around it yet, and thus hasn't reached the lava yet. So adding ores to obsidian is 100% useless, unless you want a player spreading flowing water over a lava lake to suddenly spontaneously "create" ore veins inside the new obsidian, which would just be really weird.
Sandstone is only very near the surface, right under the dirt. There is no real need to have ores in there. Just make the world generator when spawning an ore vein, NOT able to replace any of the sandstone with any ore and you're good to go.
This limits the ores to only normal stone types: specifically, stone, granite, andesite, and diorite.
- Thus since ore variations appears only in stone variations, only the ore count to determine which tool material is needed to mine it.
- You smelt the ore block in order to get it's ore, as normal. But what if you wanted just the stone base ? Gee, there was plenty of the normal stone of that type around the vein even if that stone was a "rarer" one like the new stones. There is no need to change the way to mine&smelt ores in order get both the ore plus the base stone, in the same way that there is currently no need to get "cobblestone plus iron chunks" when mining an iron ore.
Basically, ore stays ore, and this suggestion should be for looks, and extra nice looking building blocks. While changeing the way the ore mining mechanics work (all the parts about getting the ore AND the base stone) seems like something for a mod, not for vanilla.