From a ZeroHedge article this morning on gold linked ETF JNUG A...

From a ZeroHedge article this morning on gold linked ETF JNUG

A quick look at the performance of three linked assets in the past week shows additional decouplings: gold (+2.5%), GDX (+4.4%), and GDXJ (-0.03%).
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One idea voiced by "Tech Strategist" Fred Hickey is that the GDXJ ETF has seen so much demand since the recent gold bull market began 15 months, ago that it has had trouble buyiing enough Juniors that meet its criteria. Furthermore, GDXJ ownership positions ran up so high in several core names (approaching a 20% threshold) that it could effectively buy no more, going back to the original issue of ETF creation being limited by endogenous liquidity and stock technicals.
Hickey further notes that differences around the GDX/GDXJ ratio in the last week were probably due to a rebalancing, but he claims there is "no getting around GDXJ has had shortages of junior miners."
For now it is unclear if the JNUG suspended due to an investor stampede into the ETF in the last few days of the week as gold broke out, or there is simply a liquidity constraint. Both may be relevant.
Keep an eye on gold, especially as it now approaches a key breakout level.

If investors are limited in how they can allocate capital to the yellow metal, it is possible there will be fireworks.