Copper Mill - Red Mine Challenge Tomb (Part 5)

Climb back down and move around to the red ledge.

Jump to grab the bucket once more, pulling it down, raising the other bucket so the cart can roll off the end of the track.

Since the cart is now attached to the pole above, it swings forward...

...blocking the flow of water. Victory!

Pick up a bottle and craft a molotov. Then throw it at the flammable barrier. (You can do this from the ledge below the bucket or from the platform in the middle of the pit.)

Once the flames subside, jump over to the opening you just made and climb inside.

In the upstairs room you'll find containers with cloth and a Byzantine coin, 2 more coins lying in a pile, and the codex. Reading it unlocks the Bright Eyes skill, which automatically highlights nearby traps in red. You also receive 10,000 Expedition Credits the first time you raid this tomb.

Exit through the tunnel to the right of the codex, where you'll find a box of supplies...

...2 more coins, and another survival cache (18/21), buried on the left.