Ann: S&P DJI Announces December 2019 Quarterly Rebalance, page-17

The GDX purchased 71M shares last Friday (confirmed by the daily holdings at this link: https://www.vaneck.com/etf/equity/gdx/holdings/)

The rules of the ETF state that all shares must be acquired at once. The surge in activity was prior to the rebalance event. PRU trading activity was clearly out of whack with the rest of the sector a couple of weeks ago, this was the anticipation of being added to the GDX.

Note that there would have also been some activity by the GDXJ for PRU shares on Friday also and this would have made up some of the other volume up to the 91M shares traded.