A lot of mods add their own ores, and you'll need a way to place them in existing biomes for players to find. In this tutorial, we'll look at adding ores to existing biomes and biomes added by other mods. There are 2 steps that are required to add ores to biomes.

• Make a ConfiguredFeatures. This defines how your ore block is spawned.
• Use mixin to inject feature registration into DefaultBiomeFeature

We'll assume you've already created your own ore block at this point. Quartz Ore will serve as our replacement, and our goal will be spawning it in overworld biomes. Replace references to Quartz Ore with your ore when appropriate.

First we need to create a ConfiguredFeatures. Make sure to register your ConfiguredFeature at onInitialize. Feel free to change the values to suit your mod.

public class ExampleMod implements ModInitializer {
  public static ConfiguredFeature<?, ?> ORE_QUARTZ_OVERWORLD = Feature.ORE
      .configure(new OreFeatureConfig(
        OreFeatureConfig.Rules.BASE_STONE_OVERWORLD, 
        Blocks.NETHER_QUARTZ_ORE.getDefaultState(),
        9)) // vein size
      .decorate(Decorator.RANGE.configure(new RangeDecoratorConfig(
        0, // bottom offset
        0, // min y level
        64))) // max y level
      .spreadHorizontally()
      .repeat(20); // number of veins per chunk
 
  @Override
  public void onInitialize() {
    Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, new Identifier("tutorial", "ore_quartz_overworld"), ORE_QUARTZ_OVERWORLD);
  }
}

This adds your ore to the overworld biomes.

@Mixin(DefaultBiomeFeatures.class)
public class DefaultBiomeFeaturesMixin {
  @Inject(method = "addDefaultOres(Lnet/minecraft/world/biome/GenerationSettings$Builder;)V", at = @At("TAIL"))
  private static void addDefaultOres(GenerationSettings.Builder builder, CallbackInfo ci) {
    builder.feature(GenerationStep.Feature.UNDERGROUND_ORES, ExampleMod.ORE_QUARTZ_OVERWORLD);
  }
}

You should see quartz ore spawning in the overworld. You can use fill command to remove stone blocks surrounding you like this: /fill ~-4 0 ~-4 ~4 ~ ~4 minecraft:air replace minecraft:stone.