Omicron was first reported from South Africa to the World Health Organisation, which labelled the strain a "variant of concern" on Friday, prompting border closures and markets to close lower.
The S&P 500 lost 2.27% in New York on "Black Friday", a shortened day of trade after Thanksgiving.
"Across asset class we saw some of the biggest percentage changes since the pandemic breakout - case in point, the 4.7% close lower in the EU Stoxx 50 index was a 6.4 Z-score move," Pepperstone head of research Chris Weston said.
"If the new variant undermines what we have been vaccinated against then what we've seen in markets on Friday is probably not an overreaction."
The spot gold price briefly rose above US$1,800 an ounce again but was back at $1,791/oz at the time of writing.
Gold miners made gains in Australia on Friday, where St Barbara rose 2.17%.
Newmont closed up 0.85% in New York, while diversified miner and commodities trader Glencore fell 4.7% in London.