Copper Mill - Red Mine Challenge Tomb (Part 3)

Jump from the ledge near the Excavation Shaft Base Camp to the platform with the single mine cart in the middle of the huge pit.

The ledge collapses, and you must quickly press Interact to avoid falling.

Then climb onto the platform above.

There's a flammable barrier off to the left, but a torrent of water from a broken pipe above prevents you from throwing a flaming bottle into it.

Jump across to the wide ledge on the far side of the room. There are boxes of cloth and bottles here, but since you can't use them yet, just head up the stairs.

Scope out the puzzle. There's a track with 2 mine carts that ends near the torrent of water. The first cart is being held back by a dangling bucket of uranium ore, which is attached to a second bucket suspended near the ledge where you're standing. They aren't visible in this screenshot, but there are more mine carts lined up at the top end of the track in case you need them later.

Start by jumping from the red ledge to grab the closer bucket.

Lara's weight lowers the bucket, raising the second bucket and freeing the mine cart on the track above. The cart then rolls down to the end of the track, blocking the flow of water in front of the flammable barrier.

But it's not that easy. The second cart then rolls down the track and crashes into the first.

Then the track collapses. With nothing holding it back, the water continues to flow. Back to square one.