The largest ETF that invests in gold miners dropped to a fresh 52-week low on Thursday as producers saddled with higher costs continue to lag bullion prices.

Market Vectors Gold Miners (NYSEArca: GDX) was down 4% on Thursday and has shed more than 20% the past three months.

Other ETFs for this sector include Market Vectors Junior Gold Miners (NYSEArca: GDXJ) and SPDR S&P Metals and Mining (NYSEArca: XME). [ETFs for Gold and Miner Stocks]

“Capital spending by the largest gold producers is increasing at a faster pace than earnings for a second straight year as the industry’s biggest mining projects are beset by delays and surging labor costs,” Bloomberg reported Thursday.

Although gold miners posted solid first-quarter earnings, investors are worried about the potential impact to the sector if bullion prices continue to trend lower, writes James Brumley at InvestorPlace.