"I think Barrick knows a lot more about gold mining than Dr. Colliston!"
Or maybe the opposite is true. When you have so many properties It is easy to overlook them and the Gold price at that time was the triggering point for dropping properties . They didnt pass the Cost/Benefit test. As simple as that.!!!
Same thing has happened in the Oil Industry. Many Oilfields were dropped simply because they wouldnt be profitable at $9/Barrel. Now they hold most of the actual reserves!!