Short Term Trading Week Starting: 9th Apr, page-104

That calc will give you the in-situ value, however the figure has little meaning on its own. If the gold costs more to get out than it can be sold for then it doesn't matter how great the in-situ value is.

E.g. the ocean is estimated to contain several hundred trillion dollars’ worth of gold but it is in such low concentrations that there is no gold money in sea water. If I wanted to ramp the ocean I could post an in-situ value comparison which shows the ocean is undervalued when compared to the large cap ASX gold stocks. Pity the ocean doesn't have a ticker and a market cap... Although maybe some clever dealmaker could vend it into a shell.