Gold prices rose marginally Thursday in New York as the dollar index was flat on the International Exchange. Gold added 30 cents to reach $1,715.80 an ounce on the New York Mercantile\'s Comex Division. Silver also gained, adding 4 cents to $32.29 an ounce. The euro was $1.2942 from $1.2943 Wednesday. Against the yen, the dollar was 80.16 yen from 80.14 yen.