After spawning, you need to dig down for a while. Then, you no longer see an abandoned mineshaft.
How to Play Big Mineshaft & Lots of Gold Seed
This seed provides a huge source of treasures for you to discover. However, you have to overcome many challenges when playing the game.
Be careful with the surrounding lava. It requires you to decide the lava source and stop it as soon as possible. The mineshaft provides a huge source of ores, especially iron and gold. Gold seems to gain higher portion than iron.
How to Install Big Mineshaft & Lots of Gold Seed