Gold was headed for its biggest weekly gain in one-and-a-half years after rising more than 1 percent on Friday as a mid-month plunge in prices triggered bargain-hunting and a surge in physical buying across Asia. Gold was up $6.26 at $1,473.25 an ounce by 0624 GMT, off an initial high of $1,484.81, its strongest since April 15. It was poised to be up around 5 percent for the week. The metal posted its biggest daily rise since June on Thursday, but was still down 12 percent this year.