The GDX/GDXJ selling events will only affect the Canadian...

The GDX/GDXJ selling events will only affect the Canadian listing and it wouldn't surprise me if the trading action is anticipation of the rebalance.

Usually what happens is that a couple of weeks before a rebalance a few brokers (particularly in Canada) release reports on companies that are likely to do well/poorly as a result of the rebalance. The new index weights are released one week before the rebalance (this will happen this Friday night Australian time).