I was about to say that 4 tonnes of gold is the whole Zimbabwe treasury, probably worth about a gazillion Zimbabwe dollars. But then I saw that it was 4 tonnes of gold ore. The value would depend upon the concentration of gold in the ore. If, for example, the ore was 1/2% gold, the value would be about $300,000,000.
(Did I mention that those are Zimbabwe dollars? It would be less than a million in U.S. dollars.)
I'm sure you already know but just in case someone wanders along that doesn't Zimbabwe no longer has a currency. They use U.S. Dollars of South African Rands. Mugabe actually got away with paying off a large portion of their foreign debt with newly printed money until the IMF / World Bank figured out what was going on.
My son has some hyper inflationary Zimbabwe notes. One is for 15 trillion dollars. It was worth around 30 cents US when it was issued.