It is impossible to say. You could start with the market capitalisation. But what does this prove? You could buy 1 share at the current market price, or even 100,000 shares. But when you get to disclosable stakes, controlling stakes it is a different kettle of fish.

Have a look at the recent history of Astra Zenecca and the attempt of Pfizer trying to buy all the shares!

The market cap of Barrick Gold or ABX is 18.58 Billions,

If you want to buy it, you will have to make a bid higher that its value of 18.58B

How much would it cost to buy 100% of barrick gold. I know i don't have the money because the price is in the billions but I'm wondering.

How much is private and how much is public?

who owns the private shares?