Gold futures on the COMEX Division of the New York Mercantile Exchange tumbled three percent on Thursday as investors dumped risky assets,moving towards greater cash holdings amid concerns that European debt crisis is on the verge of escalating. Silver pared 6.9 percent. The most active gold contract for December delivery plunged 54. 1 dollars, or 3 percent, to 1,720.2 dollars per ounce.