U.S. stocks extended their declines, piling on heavy losses suffered at the end of last week, as markets continued to react to the pro-exit vote from the U.K. All benchmark indexes are now negative for 2016. Traders fled from risky equities into safe-haven assets such as gold. The commodity was in the midst of its best rally in seven years. Gold producers such as Randgold Resources (GOLD) - Get Report , Barrick Gold (ABX) and Newmont Mining (NEM) - Get Report were all sharply higher. Credit Suisse cut its price target on McDonald's (MCD) - Get Report , noting that the restaurant chain is far more vulnerable to the Brexit outcome than its peers. McDonald's generates 37% of its revenue from Europe. Medical device maker HeartWare (HTWR) surged after Medtronic (MDT) - Get Report agreed to a deal valued at $1.1 billion.