Gold stocks staged spring and summer rallies this year, but haven't able to sustain the momentum. Many have sold off sharply in recent weeks, along with gold. That makes this a good time to examine the book value of gold equities; are they objectively cheap now, or not?

By way of reminder, a price-to-book-value ratio (P/BV) shows the stock price in relation to the company's book value, which is the theoretical value of a company's assets minus liabilities. A stock is considered cheap when it's trading at a historically low P/BV, and undervalued when it's trading below book value. From the perspective of an investor, low price-to-book multiples imply opportunity and a margin of safety from potential declines in price.

We analyzed the book values of all publicly traded primary gold producers with a market cap of $1 billion or more. The final list comprised 32 companies. We then charted book values from January 2, 2007 through last Thursday, October 15. Here's what we found.

At the current 1.20 times book value, gold stocks aren't as cheap as they were when we ran the numbers in June, 2013, successfully pinpointing the all-time low of 0.91 (the turning point before the period in gray). Of course, that P/BV is hard to beat: it was one of the lowest values ever. And while the stocks not quite as cheap now, the valuation multiple still lingers close to its historical bottom. Remember, we're talking about senior mining companies here-producers with real assets and cash flow selling for close to their book values.

In short, yes, gold stocks are objectively selling cheaply.

The juniors, of course, have been hit harder. It's hard to put a meaningful book value on many of these "burning matches" with little more than hopes and geologists' dreams, but valuations on many are scraping the bottom, making them even better bargains, albeit substantially riskier ones.

What does this mean for us investors?

It's no surprise to see that every contraction in the ratio was followed by a major rally. In other words, the cure for low prices is low prices:

• The August, 2007 bottom (2.2) and the momentary downtrend that preceded it were quickly erased by a swift price rally leading to a January, 2008 peak (3.8).

• The bull also made a comeback in 2009-2010, fighting its way up out of what seemed at the time to be the deepest hole (1.04) in October, 2008.

Stocks have been on a long slide since the ratio last peaked at 3.24 in October, 2010, with the downturn in 2013 pushing multiples to previously unseen lows.

No one-us included-has a crystal ball, and so it's impossible to tell if the bottom is behind us. We can, however, gauge with certainty when an asset is cheap-and cash-generating companies selling for little more than book value are extraordinary values for big-picture investors.

Now let's see how these valuations look against the S&P 500.

Stocks listed in the S&P500 are currently more than twice as expensive as the gold producers. That's not surprising given how volatile metals prices can be and how unloved mining is-but is it rational? Note that despite the downtrend in the last month, the multiple for the S&P500 remains close to a multiyear high.

In other words, yes, the S&P 500 is expensive.

This contrast points to an obvious opportunity in our sector.

So is now the time to buy gold stocks? Answer: our stocks are good values now, and, if there is a larger correction ahead, they may well become fantastic values, briefly. Either way, value is value, on sale.

As the most successful resource speculators have repeatedly said: you have to be a contrarian in this sector to be successful, buying low and selling high, and that takes courage based on solid convictions. Yes, it's possible that valuations could fall further. However:

The difference between prices and clear-cut value argue for going long and staying that way until multiples return to lofty levels again-which they've done every time, as the historical record shows.

With a long-term time frame in mind, whatever happens in the short term is less of a concern. Building substantial positions at good prices in great companies in advance of what must transpire sooner or later is what successful speculation is all about. This is how Doug Casey, Rick Rule, and others have made their fortunes, and it's why they're buying in the market now, seeing market capitulation as one of the prime opportunities of the decade.

That's worth remembering, especially during a downturn that has even die-hard gold bugs giving up.

Bottom line: "Blood in the streets" isn't pretty, but it's a good thing for those with the liquidity and courage to act.

What to buy? That's what we cover in BIG GOLD. Thanks to our 3-month full money-back guarantee, you have nothing to lose and the potential for gains that only a true contrarian can expect.

The article Blood in the Streets to Create the Opportunity of the Decade was originally published at caseyresearch.com