Chests
There are currently 2 types of chests with more to come
You can get gems and armor from chests
Chests can be obtained from the mine
If you get a chest, that minecart will not deliver any ore that round.
Chances
tc levels 0 - 100 < 1/1000 of the carts will be chests - <0.1%
tc levels 100 - 200 1/1000 of the carts will be chests - 0.1%
tc levels 200 - 300 1/500 of the carts will be chests - 0.2%
tc levels 300 - 400 1/250 of the carts will be chests - 0.25%
tc levels 400 - 500 1/150 of the carts will be chests - 0.67%
tc levels 500 - 600 1/125 of the carts will be chests - 0.8%
tc levels 600 - 700 1/112 of the carts will be chests - 0.89%
tc levels 700+ 1/100 of the carts will be chests - 1%
Chest (requires 3 Keys)
Crate (requires 1 key)