Gold prices and gold mining stocks collapsed Thursday as the World Gold Council reported that global gold demand fell sharply in the third quarter from the year-ago period because of global weakness, high prices and slower demand from China. Gold market watchers expect prices to fall much further before finding a floor. In midday trade, spot gold prices sank 0.69% to $1,716.60 an ounce. SPDR Gold Shares (GLD), tracking a 10th of an ounce of