As Fareastern pointed out, Deposit is usually paired with the ability to Withdraw like your bank account. This is a pretty specific type of transaction whereas almost everywhere else in the game Buy is used.

Given how underwhelming the 500~5000 rewards are, I made the same assumption that you would either get the ingots back after 6 days or they would be converted to coupons. Given this being the one year anniversary I expected way more.