The 'formula' is pretty basic - It is what Bill Cara was using to assign his estimate of $11.50 back in the day when Gold was no where near $1200.

When everyone tries to take the reserves and divides them by the total shares outstanding it is not a reflection of 'market value'. It does not take into account cost to extract, future price of gold or other risk.

You need to take a comparative stock and see what the Market says it's worth.