The dividend of 1.33 per share paid out on this date which cut CH by that amount.
The Premium over NAV has averaged -10% since February 1999 (when data for xxchx starts) but had climbed from single digits at the beginning of September to +27% on 9/19 - which, coincidentally is when the x-dividend date was. The premium then declines quickly to single digits by 9/26. My opinion is that investors were buying up the stock for a quick 6% dividend and then dumping their shares. btw, the only other time the premium over NAV has eclipsed 20% is January, 2006.
Probably adding to the premium was the precious metal fervor in September which seems to have subsided, and then perhaps there was some shorting when the premium got so high to drive it back down (???). I think these are secondary to the dividend though.
I received something saying I could take cash or reinvest the dividend. It also notes that they would be buying shares on the open market. This may drive up the premium again, depending on what shareholders choose.