Oppenheimer Upgrades U.S. Silica Holdings To Outperform By: Benzinga via Benzinga June 11, 2015 at 08:39 AM EDT Analysts at Oppenheimer upgraded U.S. Silica Holdings Inc (NYSE: SLCA) from Perform to Outperform. U.S. Silica Holdings shares have ... Read More >> Related Stocks: U.S. Silica Holdings Inc