A little rule-of-thumb formula from from Resource World's "How to Profit from Mining" for estimating the value of an exploration mining company:

Multiply the total ounces by 20% times the price of gold and divide by number of shares.

For MAG, we'd need to use "Gold Equivalent Ounces", which is simple enough to calculate. At today's metal prices, MAG's 189.5M oz Ag, 567k oz Au, 456M lbs Pb and 769M lbs Zn equates to ~3.99M gold-equivalent oz.

So, for MAG we get 20% x 3.99M oz x $894/oz / 49,210,566 shares = $14.50/share.

Interestingly enough, this corresponds rather well to what my cash flow model for the Juanicpio JV produces with a 10% Discount Rate, if I take out the $1/share I grant for the other properties.