Nico's More Mines is a Minecraft mod that enhances your world with a plethora of new mine structures. With distinct lengths, loot, and variety, the mines include Oak Mines, Spruce Mines, and Ancient Mines.
Oak Wood Mineshaft
The Oak Wood Mineshaft is a natural occurrence that can be found beneath various biomes, including Plains, Forest, Birch Forest, Dark Oak Forest, Flower Forest, Swamp, Mangrove Swamp, Jungle, Savanna, Desert, Badlands, and Mushroom Island.
Spruce Wood Mineshaft
The Spruce Wood Mineshaft can be found naturally generated under the Snowy Tundra, Mountains, Meadow, Grove, and Taiga biomes.
Minecraft's Ancient Mines can be found in all underground levels.