Gold miner ETFs continue to drastically underperform bullion prices. Gold producer stocks are posting their weakest relative performance to bullion in over three years.

Market Vectors Gold Miners (NYSEArca: GDX) was down 9.3% year to date as of April 16, while SPDR Gold Shares (NYSEArca: GLD) gained 5.6%, according to Morningstar.

The relationship between gold miners and bullion “has gotten to an extreme enough level that I believe something major will occur over the next few months,” says Robert Sinn at the Stock Sage blog.

He sees two likely outcomes. “Gold could fall substantially (over $100/ounce) which would make the current valuations of the miners more reasonable on a relative basis,” or gold miners will rally and “revert to the mean.” [Capitulation Time for Gold Miner ETFs?]

Russ Koesterich, global chief investment strategist at iShares, says investors need to understand that gold and gold miners are distinct asset classes that can behave very differently.