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. There are 2 steps that are required to add ores to biomes.

• Make a ConfiguredFeatures. This defines how your ore block is spawned.
• Use Biome Modification API in Fabric API to add your feature to biomes.

Note that the Biome Modification API is marked as experimental. If the API doesn't work, consider using the mixin version.

We'll assume you've already created your own ore block at this point. Wool block will serve as our replacement throughout this tutorial. Replace references to wool with your ore when appropriate.

In this section, our goal will be spawning the ore in the overworld.

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

public class ExampleMod implements ModInitializer {
  private static ConfiguredFeature<?, ?> ORE_WOOL_OVERWORLD = Feature.ORE
    .configure(new OreFeatureConfig(
      OreFeatureConfig.Rules.BASE_STONE_OVERWORLD,
      Blocks.WHITE_WOOL.getDefaultState(),
      9)) // vein size
    .decorate(Decorator.RANGE.configure(new RangeDecoratorConfig(UniformHeightProvider.create(
    YOffset.fixed(0), 
    YOffset.fixed(64)))))
    .spreadHorizontally()
    .repeat(20); // number of veins per chunk
 
  @Override
  public void onInitialize() {
    RegistryKey<ConfiguredFeature<?, ?>> oreWoolOverworld = RegistryKey.of(Registry.CONFIGURED_FEATURE_WORLDGEN,
        new Identifier("tutorial", "ore_wool_overworld"));
    Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, oreWoolOverworld.getValue(), ORE_WOOL_OVERWORLD);
    BiomeModifications.addFeature(BiomeSelectors.foundInOverworld(), GenerationStep.Feature.UNDERGROUND_ORES, oreWoolOverworld);
  }
}

You should see wool spawning in the overworld. You can use below command to remove stone blocks surrounding you.

/fill ~-8 0 ~-8 ~8 ~ ~8 minecraft:air replace minecraft:stone

In this section, based on the code in the previous section, we will add the ore to the nether biomes.

We have to replace OreFeatureConfig.Rules.BASE_STONE_OVERWORLD with OreFeatureConfig.Rules.BASE_STONE_NETHER because blocks used as base block are different in the overall biomes and the nether biomes.

public class ExampleMod implements ModInitializer {
  private static ConfiguredFeature<?, ?> ORE_WOOL_NETHER = Feature.ORE
    .configure(new OreFeatureConfig(
      OreFeatureConfig.Rules.BASE_STONE_NETHER, // We use OreFeatureConfig.Rules.BASE_STONE_NETHER for nether
      Blocks.WHITE_WOOL.getDefaultState(),
      9))
    .decorate(Decorator.RANGE.configure(new RangeDecoratorConfig(
      0,
      0,
      64)))
    .spreadHorizontally()
    .repeat(20);
 
  @Override
  public void onInitialize() {
    RegistryKey<ConfiguredFeature<?, ?>> oreWoolNether = RegistryKey.of(Registry.CONFIGURED_FEATURE_WORLDGEN,
        new Identifier("tutorial", "ore_wool_nether"));
    Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, oreWoolNether.getValue(), ORE_WOOL_NETHER);
    BiomeModifications.addFeature(BiomeSelectors.foundInTheNether(), GenerationStep.Feature.UNDERGROUND_ORES, oreWoolNether);
  }
}

In this section, based on the code in the overworld section, we will add the ore to the end biomes.

We replace OreFeatureConfig.Rules.BASE_STONE_OVERWORLD with new BlockMatchRuleTest(Blocks.END_STONE) because endstone is used as a base block in the end biomes.

public class ExampleMod implements ModInitializer {
  private static ConfiguredFeature<?, ?> ORE_WOOL_END = Feature.ORE
    .configure(new OreFeatureConfig(
      new BlockMatchRuleTest(Blocks.END_STONE), // base block is endstone in the end biomes
      Blocks.WHITE_WOOL.getDefaultState(),
      9))
    .decorate(Decorator.RANGE.configure(new RangeDecoratorConfig(
      0,
      0,
      64)))
    .spreadHorizontally()
    .repeat(20);
 
  @Override
  public void onInitialize() {
    RegistryKey<ConfiguredFeature<?, ?>> oreWoolEnd = RegistryKey.of(Registry.CONFIGURED_FEATURE_WORLDGEN,
        new Identifier("tutorial", "ore_wool_end"));
    Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, oreWoolEnd.getValue(), ORE_WOOL_END);
    BiomeModifications.addFeature(BiomeSelectors.foundInTheEnd(), GenerationStep.Feature.UNDERGROUND_ORES, oreWoolEnd);
  }
}