The Missouri pb ores are the only domestic CO resource being mined and processed for other metals; therefore, they present a viable short-term opportunity for CO production. Lead, zinc, and copper concentrates are produced from the ore. The cu concentrate can contain up to 30 pct of the CO and the pb concentrate up to 15 pct of the carbon monoxide Since CO is detrimental to the processing of the zn concentrate, the remainder of the CO is rejected to the tailings. The tailings can contain as much as 50 pct of the CO originally present in the mined ore. Researchers at the U.S. Bureau of Mines have successfully tested on a continuous basis a process that recovers a bulk sulfide concentrate from mill tailings. The concentrate contains up to one-half of the CO and from 50 to 90 pct of the pb, zn, and cu. Concentrate weight represents 10 pct or less of the total tailings.