If you want a certain ore, in your dimension.
You need to put the ore in the biome, here is an example.
public void generateSurface(World world, int x, int y, int z, Random rand)
BiomeGenBase biome = new BiomeGenBase(); something like that.
YourOre ore = new YourOre();
if (biome instanceof BiomeGenBase.YOURBIOME)
{
//add your generating stuff
ore.generate(world, x, y, z, rand);
}