I see the point you're making, but people/institutions may be selling for different reasons than what you are. There's been a LOT of money made in just about every area of the market this year with the exception of the mining sector. The Sellers might just be looking to dump their losers and still have a nice profit going into 2018 with a clean slate.
I'm still not too sure how the GDXJ selling earlier this year might be playing into some of this selling we've been seeing the last few weeks. Someone was holding millions of those shares still and they could've been unloading some of those before year end. Just my guess.
I'm not so sure this selling is over yet myself. I'll be convinced when the share price reverses and moves back into reality prices. We are at stupidly cheap prices here IMO, but that doesn't mean it can't get cheaper.
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