“The ETF in question is the VanEck Junior Gold Miners ETF (GDXJ), which tracks the MVIS Global Junior Gold Miners Index. Since early 2016, assets in the fund ballooned from a little more than $1 billion to $5.4 billion currently. Some of that was due to rising share prices — GDXJ nearly doubled from $19.80 at the start of 2016 to recently as high as $36.71, an 85 percent gain, thanks to the rebound in gold.”
http://www.cnbc.com/2017/04/12/how-an-etf-gets-too-big-for-its-index.html