UPDATE 1- Global dairy prices continue to fall at Fonterra auction

(Updates to add more detail, comment from economists) WELLINGTON, Jan 20 (Reuters) - International dairy prices continued to fall in this month's second auction held by New Zealand's Fonterra Co-operative Group, the world's largest dairy exporter. The GDT Price Index, which covers a variety of products and contract periods, dropped 1.4 percent, with an average selling price of $2,405 per tonne, in the auction held on Tuesday. Whole milk powder, which makes up the bulk of the auction,