wilson's assumptions - are they valid?, page-16

but if there was a buy out maybe there are other factors also to look at.
On the negative
The discount rate may be low because the opportunity cost of the money for the buyer is probably calculated at what the buyer could get for the money if invested in a bank. But the bank money will have a lower risk than an investment in a mine so guessing a risk factor cost should also be applied in a calculation which will lower the effective NPV.
On the positive
The internal rate of return may be higher for a bolt on aquisition as many of the variable costs can be spread over the total enterprise through synergies, ie lower smeltering charges and/or lower administration charges.
I am no mining expert (do have a valuation degree but in commercial realestate and farming/forestry from another life)anyway welcome to be refuted !