Retired, gold more than anything needs to be bought/sold in a contrarian fashion. Buy more when your guts are screaming to sell the shares that you're holding. Sell some when you're in love with the stock. Emotional distress too high (and it happens to ALL of us)? That means you're in too-heavily. So, next time, buy small enough amounts that you can hold them without getting as cranked up.
This isn't my opinion, this is what Jim Sinclair preaches (sell 'rhino horns', buy 'bent fishing rods'), what Stewart Thomson advocates, etc.. It only works with a share that's headed up, in the longer trend - you have to be correct on fundamental value. But it'll add profits/shares to your account like you won't believe. As Thomson says, volatility is your free leverage.
MUX is volatile as hell. I'm not saying sell your core holdings, but next time it's way up, or next time it's way down...do a little contrary trading.