Gold is back. The shiny metal has gained 17 percent this year as investors have moderated projections of U.S. economic growth. The surge has been enough to entice hedge fund guru George Soros — who once called gold “the ultimate bubble” — to buy into gold funds and related stocks, filings showed this week.

Behind rising gold prices are a number of factors. Investors have pushed back their expectations for Federal Reserve interest rate hikes, which tend to make gold a less attractive investment compared with the U.S. dollar. Meanwhile, currency prices have fallen in top mining countries, including South Africa and Russia, making exports cheaper.

The bump in gold prices has meant a bonanza for miners. The value of top gold company stocks tracked by Bloomberg has more than doubled in 2016 as producers have reversed a yearslong slide.

Major gold miners suffered as gold fell from a peak of $1,883 an ounce in 2011 to bottom out at $1,062 last December. Those companies took on mountains of debt and shed assets to remain solvent, but now, with gold prices on an upswing, these leaner companies are pulling in higher profit margins and shrugging off debt.

In the first quarter, Soros piled $124 million into the SPDR Gold Trust, the largest exchange-traded gold fund in the world. He also bought up 19.4 million shares of Barrick Gold Corp. (NYSE:ABX), a stake currently valued at $264 million. Soros has been joined by fellow hedge fund heavyweights, including Barry Rosenstein of Jana Partners.

It’s not a sure bet, however, as Fed officials continue to signal their willingness to raise interest rates in June, potentially hobbling gold’s rise. Jeffrey Lacker, president of the Federal Reserve Bank of Richmond, told the Washington Post Monday, “The case for raising rates looks to be pretty strong in June.”

Investors remain skeptical, however, with futures markets pricing in a mere 7.5 percent chance the Fed will move next month, according to data provided by CME Group.