An Investigation Of The Effect Of Elemental Composition And Gold Grain Size On Gold Analysis And Recovery At Otjikoto Gold Mine

Abstract

Gold extraction from different type of ores is largely driven by elemental compositions and gold particle size and distribution. Another major factor that contribute to inaccurate gold analysis/ estimation is the nugget effect (presence of gold particulates in different sizes and shapes). Therefore the purpose of the study was to quantify and evaluate the effect of different elements on gold extraction/analysis, establish gold particle size distribution and determine the most suitable analytical technique that will effectively give accurate gold values in different samples from different host rocks in the Otjikoto mine gold deposit or other nugget gold ores. Sulphur (when present at the concentration of more than 2%), Iron (when present at the concentration more than 4%) and copper (when present at concentration at concentration more than 10 ppm) were found to be the major elements that cause concerns with both leaching and fire assaying. It was also determined that gold in both Otjikoto and Wolfshag occurs as nuggets and for all the samples analysed more than 50% of gold is reporting in +106 µm fractions. The three gold analysis techniques used found that Leachwell assisted cyanide leaching is the ideal method for gold analysis as it is mineralogical/elemental independent, less prone to errors and gave results which are the average of the other techniques used. Aqua regia, direct fire assay, cyanide leaching without leachwell and mixed acids techniques were found to be very sensitive to elemental compositions and gold particle sizes (nugget effect). It was discovered also that when analysing Leachwell solutions on the AAS, precipitates forms that clog the burner and the nebuliser, hence it is recommended that DIBK extraction is performed to prevent clogging.