PlacedFeature.java

// FORGE
@Mod(Test.MODID)
public class Test {
    public static final String MODID = "test";

    // A Feature + Config to say how the feature should generate. 
    public static ConfiguredFeature<?, ?> CUSTOM_ORE_CF;
    // A ConfiguredFeature + 0 or more Placement Modifiers that tells the
    // ConfiguredFeature where and how often it should generate in chunks.
    public static PlacedFeature CUSTOM_ORE_PF; 

    public Test() {
        FMLJavaModLoadingContext.get().getModEventBus().addListener(this::setup);
        MinecraftForge.EVENT_BUS.addListener(this::biomeModification);
    }

    public void setup(final FMLCommonSetupEvent event) {
        event.enqueueWork(() -> {
          CUSTOM_ORE_CF = Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, new ResourceLocation(Test.MODID, "test_ore_cf"),
                Feature.ORE.configured(new OreConfiguration(
                        new TagMatchTest(BlockTags.BASE_STONE_OVERWORLD), // The blocks this ore can replace.
                        Blocks.DIAMOND_BLOCK.defaultBlockState(), // The ore block to place.
                        10, // The size of the vein. Do not do less than 3 or else it places nothing.
                        0.2f // % of exposed ore block will not generate if touching air.
                )));

          CUSTOM_ORE_PF = Registry.register(BuiltinRegistries.PLACED_FEATURE, new ResourceLocation(Test.MODID, "test_ore_pf"),
                CUSTOM_ORE_CF.placed(
                        CountPlacement.of(25), // How many attempts per chunk to spawn this feature.
                        InSquarePlacement.spread(), // Randomizes the x/z so it is in a random 0-15 spot in the chunk. 
                        HeightRangePlacement.uniform( // Equal chance for any height in the following range:
                                VerticalAnchor.aboveBottom(20), // Bottom of spawn range starts 20 blocks above world bottom.
                                VerticalAnchor.belowTop(50)), // Top of the spawn range starts 50 blocks below world max height.
                        BiomeFilter.biome()) // Needed to allow the feature to spawn in biomes properly.
                );
        }
    }

    public void biomeModification(final BiomeLoadingEvent event) {
        Biome.BiomeCategory category = event.getCategory();
        if(category != Biome.BiomeCategory.NETHER && category != Biome.BiomeCategory.THEEND && category != Biome.BiomeCategory.NONE) {
            event.getGeneration().addFeature(GenerationStep.Decoration.UNDERGROUND_ORES, CUSTOM_ORE_PF);
        }
    }
}


// FABRIC (Mojmap)
public class Test implements ModInitializer {
    public static final String MODID = "test";
    
    // A Feature + Config to say how the feature should generate. 
    public static ConfiguredFeature<?, ?> CUSTOM_ORE_CF;
    // A ConfiguredFeature + 0 or more Placement Modifiers that tells the
    // ConfiguredFeature where and how often it should generate in chunks.
    public static PlacedFeature CUSTOM_ORE_PF; 

    @Override
    public void onInitialize() {
        CUSTOM_ORE_CF = Registry.register(BuiltinRegistries.CONFIGURED_FEATURE, new ResourceLocation(Test.MODID, "test_ore_cf"),
              Feature.ORE.configured(new OreConfiguration(
                      new TagMatchTest(BlockTags.BASE_STONE_OVERWORLD), // The blocks this ore can replace.
                      Blocks.DIAMOND_BLOCK.defaultBlockState(), // The ore block to place.
                      10, // The size of the vein. Do not do less than 3 or else it places nothing.
                      0.2f // % of exposed ore block will not generate if touching air.
              )));

        CUSTOM_ORE_PF = Registry.register(BuiltinRegistries.PLACED_FEATURE, new ResourceLocation(Test.MODID, "test_ore_pf"),
              CUSTOM_ORE_CF.placed(
                      CountPlacement.of(25), // How many attempts per chunk to spawn this feature.
                      InSquarePlacement.spread(), // Randomizes the x/z so it is in a random 0-15 spot in the chunk. 
                      HeightRangePlacement.uniform( // Equal chance for any height in the following range:
                              VerticalAnchor.aboveBottom(20), // Bottom of spawn range starts 20 blocks above world bottom.
                              VerticalAnchor.belowTop(50)), // Top of the spawn range starts 50 blocks below world max height.
                      BiomeFilter.biome()) // Needed to allow the feature to spawn in biomes properly.
              );

        BiomeModifications.create(new ResourceLocation(Test.MODID, "add_custom_ore_1")).add(
                  // We are adding so we specify the additions stage
                  ModificationPhase.ADDITIONS,
                  
                  // What check to use to determine if a biome should receive our feature.
                  // Use this instead of `BiomeSelectors.foundInOverworld()` because that helper method is currently
                  // broken and will not work for json/modded biomes injected into the Overworld.
                  (context) -> {
                      Biome.BiomeCategory category = context.getBiome().getBiomeCategory();
                      return category != Biome.BiomeCategory.NETHER && category != Biome.BiomeCategory.THEEND && category != Biome.BiomeCategory.NONE;
                  },

                  // What to do witht he biome that passed the above check. here we add out feature to the biome.
                  context -> context.getGenerationSettings().addBuiltInFeature(GenerationStep.Decoration.UNDERGROUND_ORES, CUSTOM_ORE_PF));
   
    }
}