Mineralogical study of gold ores at the Casa Berardi Mine, Quebec

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At Hecla Mining Company's Casa Berardi Mine, Quebec, the recovery rates of gold are variable, but the causes of the variability are not fully understood. Two key parameters that have been identified by Hecla geologists are Preg robbing (the preferentially absorption of gold on carbonaceous material) and the arsenic concentrations of the ore. Ultimately, the solutions to both of these problems require a better understanding of the ore mineralogy and the carbonaceous material at the mine. The investigation of the carbonaceous material will consist of analyses by Raman spectroscopy and the relationships between gold and arsenic whole rock concentrations will be investigated using a combination of petrography, scanning electron microscopy (SEM), electron microprobe (EMP) and secondary ion mass spectrometry (SIMS) analyses. Petrography will establish the distribution (e.g., as inclusions within arsenopyrite or as 'free gold' etc.) and sizes of gold particles; SEM analyses will confirm the gold mineralogy and provide a first estimate of arsenopyrite compositions; EMP analyses will establish the major and trace element compositions of arsenopyrite and SIMS analyses will determine the gold concentrations in arsenopyrite. All of these analyses will be carried out on samples that are representative of different zones of mineralization. The analyses of the ore and carbonaceous material will then be interpreted in terms of which characteristics are associated with lower recovery rates. The potential benefit of this study to the company is that, by knowing which mineralogical factors influence gold recovery, mineral processing can be made to be more efficient. Improving the efficiency of gold mining can have a significant economic impact, which benefits Canadian society as a whole.