Gold miner exchange traded funds (ETFs) have been outperforming gold ETFs for the last month. Gold certainly hasn’t been a slouch this year, at least managing to grip tight to its current price levels. But why are gold miners leaving them in the dust?

Market Vectors Gold Miners (NYSEArca: GDX) is up 4.9% in the last month, compared to SPDR Gold Shares (NYSEArca: GLD), which is up 2.4% in the same time frame. Market Vectors Junior Gold Miners (NYSEArca: GDXJ) has done even better, up 9.3% in the last month. What gives?

One big reason may be that gold miners are simply enjoying improved profit margins. Although the price of gold has inched up or gone sideways this year, gold miners are benefiting from the elevated prices.

Of course, that has its limits.

Many investors are under the impression that gold miner shares are going to yield two to three times the leverage that gold stocks do. Alix Steel for The Street reports that just because gold prices go up, it doesn’t mean small amounts of additional revenue drops to the bottom line.