acid leaching pilot plant for silica sand. 2012 - USGS Mineral Resources Program - U.S. Geological Survey. on a reduction and acid-leaching process that would produce. 18,000 t/yr ... a 12-metric-ton-per day pilot plant. inco completed a feasibility ..... listed, chromite, copper, crushed stone, gold, iron, manganese, silica sand, and silica are produced,.