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Session Chairpersons: William Petruk, Consultant, Former Chief Mineralogist, CANMET, Ottawa; S.K. Chryssoulis, AMTEL, London, Ontario, Canada
8:30 am KEYNOTE
TEXTURES OF GOLD MINERAL PHASES RELATED TO HEAP LEACHING: William Petruk, Consultant, Former Chief Mineralogist, CANMET, Ottawa, Canada K1A OG1
Native gold and electrum are the main gold minerals recovered by heap leaching. Recovery depends on ore textures that influence exposure during crushing and grinding in preparation for heap leaching. Textures include gold-bearing veinlets along fractures and microfractures, and gold occurrences along grain boundaries. Small encapsulated gold grains in quartz, pyrite and arsenopyrite are not likely exposed, and generally non-recoverable. Similar submicroscopic forms of gold are not recoverable by heap leaching. Detailed studies have shown that many so-called encapsulated gold grains may occur either along weakly bonded grain boundaries or microfracture in minerals, which become exposed by fine grinding. Ore textures in various ores will be reviewed. Ore types include gold in arsenopyrite-pyrite-quartz veins, gold-chalcopyrite deposits, disseminated gold in sediments, Carlin-type gold ores, gold-pyrite associations, and gold in volcanogenic ores, etc.
MINERALOGIC EVALUATION OF UNLEACHED GOLD IN BIOOXIDIZED LEACH RESIDUES: S.K. Chryssoulis, AMTEL, London, Ontario, Canada N6G 4X6; Rong Yu Wan, Newmont Metallurgical Services, Salt Lake City, UT 841O8
Gold associations were established in a biooxidized, chlorinated CIL residue assaying 0.02 oz Au/t and in a biooxidized thiosulfate leach residue assaying 0.01 oz Au/t. Detailed Mineralogic study involved: assays of screened fractions; light microscopy; ion probe microanalysis to quantify 'invisible' gold in sulfide minerals; proton probe microanalysis to detect submicroscopic gold in chert; and laser microprobe analysis to detect and quantify preg-robbed gold. In the CIL residue most of the gold is preg-robbed (71%). In the thiosulfate leach residue, gold occurs mainly as submicroscopic disseminations in microcrystalline quartz (chert). In both residues the 'invisible' gold in pyrite accounts for a minor fraction of the gold assay. Quantitative determination of the gold occurrence in the two residue samples established conclusively that gold adsorption on carbonaceous matter in the thiosulfate leach is of minor importance.
PROCESSING OPTIONS FOR HEAP LEACHING CARBONACEOUS SULFIDIC GOLD ORES: G. Ramadorai, President, EnMet Associates, Inc., 11225 E. Quick Draw Place, Tucson, AZ 85749-9551
This paper addresses processing options for recovering gold from carbonaceous sulfidic gold ores. These include, but not limited to, the following methods: (1) Hypochlorite pretreatment followed by cyanidization; (2) Chemical blanking agents pretreatment followed by cyanidization; (3) Non-cyanide heap leaching techniques; (4)Biological pretreatment followed by cyanidization; (5) Biological pretreatment followed by non cyanide heap leaching. Issues of costs, economics, recoveries, testing methods, state of advancement etc., will be discussed in the paper.
10:00 am BREAK
GEOLOGY AND CHARACTERISTICS OF GOLD MINERALIZATION IN FOUR SIBERIAN GOLD DEPOSITS, RUSSIA: A.D. Genkin, N.S. Bortnikov, Y.G. Safonov, IGEM, Russian Acad. of Sciences, Moscow, Russia; L.J. Cabri and G. McMahon, CANMET, 555 Booth St., Ottawa, Canada K1A OT1; C.J. Stanley, Natural History Museum, London, U.K.; F.E. Wagner, D.J. Friedl, Physik-Dept., Technische Univ., Munchen, Germany
A multidisciplinary investigation (SIMS, EPMA, Mossbauer) was used to characterize gold in four Siberian mesothermal sulfide gold deposits: Olympiadnenskoe and Veduginskoe within the Enisei Mountain Range and Nezhdaninskoe and Sentachan in the Verchoyansk-Kolyma area. It was found that some of the mineralization is refractory in all four deposits, occurring in large part as "invisible" gold in arsenopyrite and a lesser amount in pyrite. The gold concentration and distribution vary considerably, both within and between grains of arsenopyrite, with implications for processing options, such as heap leaching.
AUGMENT X4 TECHNOLOGY FROM THE LAB TO FEASIBILITY; A CASE STUDY: K.M. Schall, K.A. Brunk, G.R. Maxwell, Augment Technologies, Denver, CO 80235
Gold ores containing oxide copper incur significant cost penalties when leached with cyanide, because 4-5 moles of cyanide are consumed for each mole of leached copper. This equates to ~4 lbs of NaCN per lb of leached Cu. Total cost of excess NaCN consumption plus CN destruction can exceed $4.00 per ton of ore. AuGMENT Technologies has developed and demonstrated a new process that can: 1) economically recover 70-80% of cyanide fed to a mill; 2) produce salable copper cathodes; and 3) reduce the need for cyanide destruction facility. Standard resin processing and electrowinning equipment are used to recover the cyanide and produce copper cathodes. Steps have been taken to determine: 1) how to develop resin kinetics; 2) how the AuGMENT Process can be scaled up; 3) how much savings is incurred at mill site; and 4) how the novel 'electro-elution' circuit achieves efficient operation.
COPPER RECOVERY AND CYANIDE REGENERATION FROM CYANIDE SOLUTIONS: H. Soto and F. Nava, Dept. Mines and Metallurgy, Laval University, Quebec City, Quebec G1K 7P4
A method has been developed to recover cyanide and copper from heap leach cyanide solutions containing copper complexes and thiocyanate. Copper is precipitated as copper thiocyanate or copper cyanide, depending on pH and concentrations of thiocyanate and cyanide in effluents. Precipitates assaying over 50% Cu show good dewatering qualities and separate readily from effluents by filtration. Solutions containing bulk of cyanide are oxidized with ozone to transform remaining thiocyanate to cyanide, resulting in purified cyanide solution that can be recycled. The pH of the effluent is lowered to optimize precipitation and oxidation, and then raised to regenerate the cyanide. Recoveries are in excess of 96% of Cu and CN. Efficiencies of oxidation are 85-90%. Economic evaluation indicates a profitable process for solutions containing more than about 250 ppm copper. A bleed of barren solutions from cyanocidic gold/copper ores could be treated economically by heap leaching, since CN consumed by Cu could be regenerated at no cost.
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