This was taken from: https://www.personadeinteres.
Post# of 9903
"The next report on file is done by P.S. Friesen in October 1968. In his report he concluded that: There is an untouched vein approximately 1000 feet long at the northwest end of the old mine workings that would represent 6,750,000 tons of ore. Plus the 2000 feet of mined area at Cinco Minas could still represent additional tonnage of 12 million tons even though the high grade has been mined out. He also notes the potential of additional ore in the direction of Cerro Colorado. It must be noted that all references to ore, ore volumes, reserves, or resources are historical estimates only based on the required criteria at the time of reporting.
In summary, he feels that in the order of 20 million tons of ore are possible for extraction with an average grade of $4 to $5 / ton for the 6,750,000 tons and $1 / ton for the remaining 12 million. No estimate was given for the Cerro Colorado portion."
Now the math:
6.75MM tons @ $4/ton = $27MM
12MM tons @ $1/ton = $12MM
$39MM total @ $40/oz (1968 price)
At $1200/oz gold price...30 times the 1968 price:
$39MM x 30 = $1.17 Billion @ $1200/oz price
Of course there are extraction costs.