GEOCOAT~(TM) BIOOXIDATION DEMONSTRATION AT ASHANTI GOLDFIELDS' OBUASI OPERATIONS, GHANA, WEST AFRICA

摘要

Facing lower gold prices, gold mine operators throughout the world are seeking ways to reduce costs for treating refractory sulfide ores. Many gold mines, currently producing oxide ores, have underlying refractory sulfide deposits and the operators could extend the mine life by processing these sulfides. Fortunately, oxidation technologies for refractory ores need not be complex nor costly. GeoBiotics, Inc. has developed heap biooxidation technologies (GEOCOAT~(TM)) for treatment of refractory gold ores and concentrates. GEOCOAT~(TM) uses simple low cost unit operations common to heap leaching of gold and copper ores. The cost effectiveness and flexibility of GEOCOAT~(TM) heap biooxidation allows mining companies to expand operations to include refractory ore. In addition, GEOCOAT~(TM) can be utilized to supplement or replace existing oxidation processes such as roasting, autoclaving, or agitated tank biooxidation, and to treat a lower resource grade than is currently economic. The GEOCOAT~(TM) technology involves coating sulfide concentrates onto sized support rocks and biooxidizing the sulfides in a heap configuration. After biooxidation the concentrate is stripped from the support rock, neutralized and leached in conventional cyanidation facilities. Ashanti Goldfields Company Ltd. (AGC) produces over 885,000 ounces of gold per year from oxide and refractory ores at its Obuasi operations in Ghana. Refractory flotation concentrates are treated in roasters and in the world's largest stirred tank biooxidation facility. In August 1998, AGC and GeoBiotics jointly constructed and operated a field demonstration heap of the GEOCOAT~(TM) process at the Obuasi operations. The heap contained 1082 tonnes of support rock and 125 tonnes of concentrate. The heap was approximately 19 meters square at the base and 3.8 meters high, and ran for 88 days after which the concentrate was reclaimed. Average gold recovery after biooxidation was 91.5 percent with a NaCN consumption of 8.6 kg/t. Baseline gold recovery by direct cyanidation of the concentrate was 53.8 percent. The field demonstration project was completed in December 1998 and successfully demonstrated that the GEOCOAT~(TM) process is a technically and economically viable low cost alternative for treating concentrates and ores at the Obuasi operations. A second demonstration heap, using low-grade sulfide ore as the support rock, is currently being constructed. The potential integration of a GEOCOAT~(TM) heap biooxidation technology at Obuasi provides numerous opportunities to increase gold production, reduce cut-off grade, and reduce operating costs.