The important thing when calculating the equivalents is the...

The important thing when calculating the equivalents is the ratio of prices, not the prices themselves. CDU use a Cobalt:Copper price ratio of $26/$2 = 13:1. At current spot prices the ratio is actually $18/$4.10 = 4.4:1.

I.e at current prices 1 lb of cobalt is worth the same as 4.4 lb of copper, whereas using CDU's assumptions it is worth 13 lb. That overstates its value by 295%. Even gold is overstated using CDU's assumptions because $900/$2 = 450:1 while at current spot prices $1530/$4.1 = 371:1. Gold is pretty insignificant though, Cobalt not so.