Billion ounces of silver traded in London on Monday - LBMA

* CME raises Comex 5000 Silver Futures margins by 17.9%

* U.S. commodities regulator monitoring silver activity

* Billion ounces of silver traded in London on Monday - LBMA

* FACTBOX-How silver is traded (Adds graphics, updates prices)

Feb 2 (Reuters) - Silver slumped 8% on Tuesday as small investors turned their focus away from the metal, hastening a retreat from a rally to a near eight-year peak in the previous session fuelled by a social media-driven trading frenzy.