If you find sources that say that BZA had $800,000,000 of gold then it proves that $800,000,000 of gold in the ground is worth a $19,000,000 sale price.
Consider that that you net $200,000,000 of gold from that over 30 years at a 8% interest rate compounded annually which are broad approximations.
Using a time value of money calculator gives a present worth of -19,875,466.51. You would get less than that since that is the breakeven to the buyer.