Gold prices slip back below $4,000 a troy ounce ahead of Fed Chairman Kevin Warsh's speech at the European Central Bank Forum in Portugal. "The market has yet to attract sufficient buying interest to establish that level as support," analysts at Saxo Bank say. "Gold fell 14% during the second quarter, its worst quarterly performance since 2013, as investors continued to price in the risk that the Federal Reserve may tighten policy further in response to an inflation flare-up, despite the recent retreat in energy prices." In early European trading, New York futures slide 1.6% to $3,974 an ounce. Meanwhile, the U.S. dollar index is up 0.2% to 101.37, making dollar-denominated commodities more expensive for overseas buyers. (giulia.petroni@wsj.com)