Gold posted its biggest one-day percentage drop in 30 years Monday as new signs of a global economic slowdown emerged and fears diminished that central banks' easy-money policies would stoke inflation.

Gold futures for April delivery fell $140.40, or 9.4%, Monday to a two-year low at $1,360.60 an ounce on the Comex division of the New York Mercantile Exchange. That extended their bear-market descent of more than 20% from their 2011 all-time high. Since Thursday, gold prices have declined by more than $203 an ounce, a record...