Potential Low-Grade Iron Ore and Hydraulic-Fracturing Sand in Cambrian Sandstones, Northwestern Llano Region., Texas

The red upper unit of the Hickory Sandstone is a hematitic and goethitic sandstone containing a large reserve of potential low-grade iron ore. It is estimated that about 7 million long tons of elemental iron is locked up in each square mile of the upper 30 feet of this deposit in sandstone averaging about 12.4 percent elemental iron. At least 175 square miles of the deposit is under less than 800 feet of cover, and reserves in the upper 30 feet in this area total about 650 million long tons if 75 percent of the potential iron ore is minable and two-thirds of the iron in the mined ore is recoverable. Beneath this level another 50 or 60 feet of poorly exposed iron-bearing sandstone is probably equally as iron-rich, and if this is true, total potential reserves may be as much as 1.6 billion long tons of elemental iron in 23 billion long tons of rock or about 6 billion tons of concentrates. No part of the deposit can be regarded as direct shipping ore. Iron oxide from the red unit of the Hickory Sandstone, except for high carbonate mineral content, is of paint pigment quality. Hydraulic-fracturing sand production from the lower unit of the Hickory Sandstone is well established in the Voca area, McCulloch County, and within the area of this report the amount of such sand is very large. The middle unit of the Hickory Sandstone, the Lion Mountain Sandstone, the Welge Sandstone, and the sandstone zones in the San Saba Member appear to be devoid of deposits of value.