The ability to create and register ores as blocks is available, but the ability to tell them to generate in the world and the paramaters accompanying are not present at all, thus nullifying the purpose of creating them altogether.

:(

As I was struggeling to get this running with MMD Ore Spawn here is the code I used.
Maybe it helps you or other.

{ "block": "contenttweaker:sub_block_holder_0", "state": "sub_block_number\u003d14", "parameters": { "size": 1, "variation": 0, "frequency": 2.0, "minHeight": 25, "maxHeight": 32 }, "feature": "default", "replace_block": "default", "biomes": [] }

Complete Pastebin of orespawn.json

You'll need MMD OreSpawn for this.
I enabled the replacement of Vanilla Oregen in the ore spawn config.
In the complete Pastebin are also a few other ores (Dense Metals and Thermal Expansions)

Honestly I think this is out of the scope of ContentTweaker to a certain degree, and that other more dedicated such as MMD OreSpawn and CoFHWorld already do a good job of providing ore generating options. It would be redundant effort to have this implemented within CoT, just having the ability to register something as an ore block is more than enough.

For the most part, implementing a wrapper around Vanilla Oregen wouldn't take more than a complete minutes worth of time, and for those that only need simple ore gen, it'll be nice, especially since then you could use bracket handlers instead of contenttweaker:sub_block_3:5 which is meaningless