California agg rush
June 1, 2007 By: Bill Elverman Pit & QuarryA California producer turns gold tailings into high-quality product in a market stressed for aggregates resources.
Drive through the rural expanse of Calaveras County, Calif., and you'll see endless rolling hills spotted with cattle and farms; cherry trees and barbed-wire fences; and the gently flowing Calaveras River. Next to the country splendor of California's Central Valley also exists a cumbersome reminder of its past: piles of tailings left over from dredges used in the 1930s and 1940s to mine gold.
 The Jenny Lind plant of 711 Materials is a modular system designed to process tailings at a rate of 400 tons per hour. |
These piles of rock sat for decades as nature piled on weeds and leaves. Trees grew in the spaces between. Aggregates producers didn't touch the rock for years because demand didn't warrant it and the lengths required to turn it into a saleable product were deemed too extensive.
Time, technology and market demands have caught up to these sizeable deposits, however. Producers like 711 Materials Inc. of Modesto, Calif., have found ways to efficiently turn this waste into quality aggregates products with the right combination and utilization of material washing equipment. They're also returning the countryside to its original form – a proud reclamation of land left undesired by years of neglect.
 This aerial view shows the Eagle Iron Works product washing configuration at 711 Materials' Jenny Lind plant. |
Turning waste to gold
711 Materials built its plant in Jenny Lind, Calif., to support its concrete aggregate batch plant 25 miles away in Stockton and to provide aggregate and other products (gabion rock, class II road base) to Calaveras County. The site offers two substantial challenges:
- Much of the rock and sand is embedded with clay, roots and other ecological trash.
- Rock and sand were completely separated in the gold mining process: It must be re-blended to keep up production rates and meet strict aggregate specifications.
Steve Case, general manager, 711 Materials, admits to being skeptical at first. Companies like his turned away from these sites years ago after mining easier deposits because demand didn't require them to go through the hassle of processing the dirtiest of the tailings. Times have changed, however, as demand has increased and the number of permitted reserves in the state has decreased.
 Overhead shot of an Eagle Iron Works blade mill complete with personal safety covers. |
"What people were walking away from 10 to 15 years ago is now some of the best material you can possibly get," Case said. "Ten years from now the material we're going to be washing and scrubbing and cleaning [will be even more challenging. The shortage of permitted reserves] is one of our biggest issues. Ten years ago we didn't have an outlet for this product. Now we do."
711 Materials worked with Spaulding Equipment Co. of Perris, Calif. – a supplier of material processing equipment – to examine ways to turn tailings into high-quality aggregates at another of the company's plants in Chico. The blending issue is easy enough to solve: blend in manufactured sand with the tailings to achieve the required sand content. The clay and vegetation, however, is a more complicated matter. Spaulding representative Bob Cummings took Case to a site with similar challenges to showcase a configuration of Eagle Iron Works coarse and fine material washers that removed clay and debris from tailings and turned it into concrete aggregate.
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