For all the fanfare garnered by the world's largest gold miners, you might think they have a monopoly on the world's largest gold mines.

Think again.

Sure, the primary gold miners have staked their fair share of buried treasure. Gold Fields' (NYSE: GFI) Kloof and South Deep mines alone combine for a whopping 40 million ounces of gold reserves.

By and large, gold mother lodes like the 33.6 million ounces of proven and probable reserves at the Donlin Creek property in Alaska -- owned jointly by Barrick Gold (NYSE: ABX) and NovaGold Resources (AMEX: NG) -- are about as big as they come from the miners that primarily target gold.

Because the two metals are so often found in tandem, many of the world's largest gold mines are actually copper mines. If you're wondering how Freeport-McMoRan Copper & Gold (NYSE: FCX) achieves a cost structure for copper production of less than $1 per pound, the answer lies right in the name: gold. Freeport's core operation, the Grasberg mine in Indonesia, sports an immense gold reserve of 38.5 million ounces to accompany a copper treasure of 35.6 billion pounds.

But Grasberg may not remain the world's premier copper and gold mine for long.

Tomorrow's copper-gold mother lode
Ivanhoe Mines (NYSE: IVN) may not be the first name to roll off your tongue when you think of gold, but that may not remain the case for much longer. Ivanhoe is fast-tracking construction of the world's largest pending copper and gold mine: Oyu Tolgoi. Located in Mongolia, just 50 miles from the Chinese border, this massive deposit is uniquely positioned to satisfy China's robust demand for both copper and gold. Ivanhoe retains a 66% interest in the project, while the government of Mongolia holds 34%.

The company has built an estimated resource (measured and indicated, plus inferred) of 81 billion pounds of copper with a monster gold kicker of 46 million ounces. While the company proceeds with a construction schedule that targets open-pit production beginning in 2013, exploration drilling will endeavor to convert resources to reserves and further expand the known deposit. If their most recent drill result is any indication, investors may be in for quite a ride. In September, Ivanhoe revealed that a single drill hole encountered 938 meters of continuous copper and gold mineralization.

Ivanhoe recently announced a share offering to raise between $800 million and $1 billion toward construction of the mine. The offering is structured such that existing shareholders will be encouraged to participate in order to avoid dilution of their existing stake. Leading the charge, executive chairman and CEO Robert Friedland announced he intends to maintain his own 18.3% stake in the company. It is not yet clear whether strategic partner and 34.9% stakeholder Rio Tinto (NYSE: RTP) will follow suit. Relations between the two companies have been constrained since Ivanhoe altered its shareholder rights plan earlier this year to allow for additional strategic investors to build stakes in Ivanhoe Mines.

Moving and shaking -- Mongolia-style
The pending share offering itself is billed as a bridge to a multibillion-dollar chunk of debt financing for Oyu Tolgoi to follow during the first half of next year. Core lenders are slated to include the International Finance Corporation, BNP Paribas, and Export Development Canada. Given China's explicit policy objective to finance global gold production, I will not be surprised to see a Chinese financing entity come forward as well.

Considering the enormous scale of this project and the stakes involved, the shifts in management structure also announced this week are well received by this Fool. Executive chairman Robert Friedland is retaking the CEO position from John Macken and will lead a newly created Office of the Chairman to pursue strategic initiatives for Ivanhoe. Friedland previously served as Ivanhoe CEO through 2006. Serving as President, Macken will now hone his focus more fully upon supervising the construction effort at Oyu Tolgoi ... where a workforce of 5,300 is already onsite.

The bi-metallic bottom line
As attractive as Oyu Tolgoi's giant gold kicker may be for those like me with a bullish outlook for gold, there is no escaping the fact that the mine remains primarily a copper play. But oyu, what a copper play! Whereas significant zinc and molybdenum by-product credits permitted Southern Copper (NYSE: SCCO) to expend just pennies per pound ($0.064) to produce copper during the first half of 2010, Oyu Tolgoi is likely to achieve similar cost metrics on the basis of by-product gold production. At gold prices of $1,000, the mine's copper cost is estimated at $0.38 per pound. At current metal prices, the project sports a net asset value of $17.3 billion, which compares very favorably to the company's enterprise value of $11 billion -- and Oyu Tolgoi is not even the company's sole asset.

I believe Ivanhoe Mines presents a compelling opportunity to get in on the ground floor with a mine that is likely to oust Freeport's Grasberg as the world's largest copper / gold deposit. With additional exploration upside highlighted by recent drill results, favorable cost metrics through a range of metal price scenarios, and the scent of additional strategic opportunities waiting in the wings, Ivanhoe may just be the world's next Freeport-McMoRan. I have added Ivanhoe Mines to my silverminer CAPS portfolio, and encourage you to cast your own vote within Motley Fool CAPS today.