By Paul van Eeden
 I received an interesting question about company valuations  from one of my newsletter subscribers that I thought I would address as  a Commentary. It is a multi-part question that will take more than one  Commentary to address; this week is part one: Valuing Mining Stocks.
 Mining is a finite business. Mineral deposits contain a certain  amount of ore and when that ore is mined out the deposit is depleted, no  matter what you do or wish.
 That is in stark contrast to say, an auto parts manufacturer, who can  adapt to new demands and specification changes and (hopefully) stay in  business for many decades. When you value an auto parts company, you can  compare the company's price to earnings, price to cash flow, operating  margin and net profit margin (among other things) to the company's peers  to assess whether the stock in question is relatively cheap, or  relatively expensive. You can also get a sense of whether the stock is  cheap or expensive in an absolute sense by looking at the book value per  share and comparing things like the profit margin and dividend rate to  prevailing interest rates. But, embedded in all this (except book value  per share) is the implicit assumption that the earnings and cash flow  are for all intents and purposes infinite. When you are dealing with a  business that can be reasonably expected to continue in a similar  fashion for many decades, earnings per share, cash flow per share,  dividend rate, etc. are meaningful. That is not the case with mining.
 Take a hypothetical mining company that has only one mine as an  example. Let us assume that mine is going to produce for another five  years before the ore will be depleted. Now, let us say that the  company's price to earnings ratio is ten. A hypothetical auto parts  manufacturer also has a price to earnings ratio of ten. Based on just  this one metric, we cannot differentiate between the two stocks. Let us  also assume that the prevailing ten-year interest rate is five percent.
 This means that you can invest your money in a ten-year bond and earn  five percent per year while taking relatively little risk (other than  the risk of interest rates rising, which could negatively impact all the  investments under consideration and is therefore not considered).
 The auto parts manufacturer has a price to earnings ratio of ten.  That means for every dollar's worth of stock you buy, you expect to earn  ten cents, or ten percent, in earnings. It does not really matter for  our purposes whether those earnings are retained by the company or paid  out as a dividend since, either way, the earnings accrue to the benefit  of shareholders. Furthermore, you can reasonably assume that the auto  parts manufacturer is going to be in business for several more decades  and, because you have done lots of due diligence, you can also assume  that the future earnings are likely to be the same as the current  earnings. So, if you buy the auto parts stock, you will earn ten percent  per year as opposed to five percent on your bonds. The auto parts stock  is probably riskier than a bond; however, if you can make twice as much  money it might be tempting.
 Then you look at the mining stock and notice that it, too, has a  price to earnings ratio of ten and, therefore, you can also make ten  percent a year if you bought that stock. But you would be wrong. The  mining company's mine only has a five-year life ahead of it. So, if it  has a price to earnings ratio of ten it means that for every dollar of  stock you buy you get ten cents in earnings. But the earnings are only  going to last another five years, so your total earnings per dollar of  cost will only be fifty cents — - half of what you paid for the stock — -  and then the mine is depleted. That's why comparing a mining stock to  other investment opportunities on the basis of price to earnings, price  to cash flow, or dividend yield is complete nonsense. It is just as  futile to compare mining stocks to each other based on these metrics  because mining companies have different mine lives in their operations.
 The only reasonable way to evaluate a mining company is to look at  the net present value of the potential future cash flow, discounted at  an appropriate discount rate. You have to take into account not just the  cash flow that the mine(s) is generating, but also sustaining capital  costs (including future exploration and development costs) associated  with keeping the mine in production. Assuming you can derive a suitable  cash flow model for each mine that a company owns you can then calculate  the net present value of future cash flow by using an appropriate  discount rate to represent the geological, political, social and  financial risks. If you sum all the net present values together, add any  other assets on the balance sheet and subtract any debt, you will  arrive at the net asset value per share. In a rational world you would  expect to pay no more for a mining stock than its net asset value per  share — - how do you expect to make money if you consistently pay more  for stocks than what they are worth? But, in the real world, mining  stocks almost always trade for more than the net asset value of their  constituent mines, and for a good reason.
 Mining stocks also offer leverage to commodity prices. Take a gold  mining company as an example. Assume we have a company that mines gold  for a total cost of $400 an ounce, and let us pretend the gold price is  $500 an ounce. The net present value of the mine would be calculated  based on the $100 margin. If the gold price increases by 20% to $600 an  ounce the net present value of the mine will double, since the margin  would now be $200 an ounce. Thus the value of the company increased five  times more than the increase in the gold price. Most people buy mining  stocks because of this leverage.
 What should be immediately evident is that if you pay more for mining  stocks than what they are worth, on the speculation that the price of  the underlying commodity will increase, you are merely gambling on the  commodity price. Fortunately there is a way to quantify the premium that  one should pay for a mining stock to incorporate the leverage it has to  the underlying commodity price. There is a formula called the  Black-Scholes Model that can be used to calculate the "option" value of a  mining stock [Editor's note, you can find more information on the Black  Scholes model and further links at http://en.wikipedia.org/wiki/Black-Scholes  ]. What should be done is to calculate the discounted net present value  of the all the company's mines and then add the "option value" of the  mines as calculated by the Black Sholes formula to obtain a more  realistic asset value per share. By adding the optionality of mining  shares to the net present value of the mines themselves we can account  for the fact that mining shares trade at a premium to their net asset  value because of their leverage to the underlying commodities.
 If you calculate the net asset value of a mining stock as described  above you will get a result that can be used to compare different mining  companies to each other, and mining companies to investments in other  sectors. Unfortunately, very few mining analysts employ the Black Sholes  model to calculate mining net asset values, so for most people buying  mining stocks really comes down to blind speculation on commodity  prices.