(Kitco News) - Although gold prices are holding support above $4,000 an ounce, June proved to be a difficult month as rising opportunity costs continued to push investors out of gold-backed exchange-traded funds, according to the latest report from the World Gold Council.In its monthly ETF report, the WGC said that 74.3 tonnes of gold, valued at nearly $9 billion, flowed out of the ETF market last month. However, despite the ongoing liquidation, the global ETFs ended the first half of the year o