Yellen formerly chaired the US Federal Reserve and made the remark in recorded comments for a virtual event held yesterday.
"Gold has kicked back to US$1,777 [an ounce] … even though real Treasury yields have moved further negative, which perversely was the source of inspiration behind the move higher yesterday," Pepperstone head of research Chris Weston said.
Copper gained as London returned from a bank holiday, while China returns on Thursday.
The red metal rose 1.4% to $9,966.75 per tonne, having risen above $10,000/t last week to its highest point since February 2011.
Copper stocks in London Metal Exchange warehouses fell for a second week in a row, down 7.7% to 143,725t, the lowest since April 6, Marex Spectron's Anna Stablum noted.
Among the mining majors, Fresnillo rose 3.38% in London.
Freeport-McMoRan gained 1.32% in New York.
Finally, Barrick Gold fell 0.88% in Toronto.