Mumbai, Aug. 21 -- Silver futures surged towards $79 an ounce on Friday and were on track for a third consecutive weekly gain, supported by safe-haven demand amid heightened currency and bond-market volatility. Silver has gained more than 4% this week as the US Treasury's decision to at least double long-term bond buybacks pushed Treasury yields and the dollar lower. The dollar index slipped 98.6 on Friday and was on track to lose nearly 1% for the week, as the US government's bond buyback plan heightened market volatility. Falling yields reduced the opportunity cost of holding non-yielding silver, while rising oil prices and renewed inflation concerns further strengthened demand for precious metals. Meanwhile, MCX September delivery traded...