Ann: Duckhead Exploration Update, page-53

The mandate of the Van Eck managed GDXJ is to have complete exposure to the junior and mid cap gold sector. The selling as I understand it is an arithmetic adjustment based on market cap as a percentage of the GDXJ index.

You can actually track the holdings daily at:

http://www.vaneck.com/market-vectors/equity-etfs/gdxj/holdings/

Van Eck have gone from 52.6M on 24/12 to 48.8M at close on tuesday. I don't think they would be selling the huge number of shares traded today though.