Pressure Oxidation problems and solutions: Treating carbonaceous gold ores containing trace amounts of chlorine (halogens)

Santa Fe Pacific Gold Corp. conducted pressure-oxidation pilot plant studies on refractory carbonaceous gold ores from the Twin Creeks Mine in Nevada. The tests were conducted at Hazen Research Inc., Golden, CO, during 1993 and 1994. Laboratory investigations using CIL cyanidation after batch pressure oxidation demonstrated gold recoveries of 90% to 95%. However, pilot plant testing showed that several of the same ore types responded very poorly, with gold extractions of only 45% to 75%. Plant testing was suspended for approximately four months while extensive research was conducted to determine why these ores responded poorly and to identify potential solutions. This paper describes the batch and pilot plant test results, the extensive research activities that eventually identified the cause of the gold recovery problem and the final semicontinuous and continuous pilot plant operations that confirmed possible solutions. Final pilot plant results showed gold recoveries that were consistently greater than 90%.