According to BMO Capital Markets, there will be a massive rebalance trade around the GDXJ ETF rebalances in June 2017, including significant demand for around 18 potential new additions, as well as a large selling of existing GDXJ names. There are some huge flows around these gold names, with an average daily trading volume of eight days of volume. The ETF will need to sell $3 billion worth of its existing holdings to buy the new additions, which will create a massive funding trade significantly impacting existing names. On this note, don’t think you can front run the front runners. The brokers, which are Authorized Participants to create the shares for the ETF, will spend the next eight weeks going short and long the expected index changes, largely excluding any outside parties from getting a piece of the trade. Speculators who show up to trade on the rebalance date likely won’t get the price they expect. So over the next eight weeks, we may see some market impact from the pre-rebalance of the index, but keep in mind the GDXJ ETF is about supplying beta to investors. They need the most liquid names to deal in, but this will be a great opportunity to pick up some small-capitalization, high- quality growth names that deliver alpha to investors.

This means current underperformance of GDXJ will last another 7 weeks! This is really a set back for any holder of GDXJ, as after mid June the index will hold 60% new holdings, mainly MID/large caps like AUY, IAG, OGC, EGO, HL, CDE,…

Maybe some recently created Mid Cap names like TREK, LMC,… could be included

This is really crazy, as every gold stock investor holding Small cap names /Mid caps names with market cap 75 m- 1.5 Billion that are in GDXJ will underperform the next 7 weeks. After that the GDXJ will certainly outperform a little bit, but not as before, so I understand investors selling GDXJ and buying the individual midcaps is a better strategy.

http://www.etf.com/sections/features-and-news/popular-gold-miners-etf-change-dramatically?nopaging=1