AN INVESTIGATION OF THE EFFECT OF ELEMENTAL COMPOSITION AND GOLD GRAIN SIZE ON GOLD ANALYSIS AND RECOVERY AT OTJIKOTO GOLD MINE A RESEARCH THESIS SUBMITTED IN FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CHEMISTRY OF THE UNIVERSITY OF NAMIBIA BY FILLIPUS HAULOFU THOMAS 200843427 2019 MAIN SUPERVISOR: Prof A.F. Kamona (Department of Geology, University of Namibia) CO-SUPERVISOR: Dr. V. Uahengo (Department of Chemistry and Biochemistry, University of Namibia) 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. i List of publications/conference proceedings N/A ii Table of contents Contents Page Abstract ...................................................................................................................................... i List of publications/conference proceedings ............................................................................. ii Table of contents ...................................................................................................................... iii List of tables .............................................................................................................................. v DECLARATIONS ................................................................................................................... ix Chapter 1. Introduction .............................................................................................................1 1.1. Background of the study ...........................................................................................1 1.2. Statement of the problem ..........................................................................................2 1.3. Objectives of the study ..............................................................................................2 1.4. Hypothesis of the Study ............................................................................................3 1.5. Significance of the study ...........................................................................................3 1.6. Limitations ................................................................................................................3 1.7. Delimitations .............................................................................................................4 Chapter 2. Literature Review ....................................................................................................4 2.1. Outline of Geology and Mineralization of Otjikoto mine gold deposit. ...................4 2.2. The factors affecting gold analysis and recovery ......................................................6 2.2.1. Gold particle size ..............................................................................................7 2.2.2. Association of gold with other elements/minerals which can interfere with its recovery or analysis. ...................................................................................................... 10 2.3. Gold analysis/recovery techniques and methodologies. ........................................ 11 Chapter 3. Methodology ........................................................................................................ 22 3.1. Research Design .......................................................................................................... 22 3.2. Sampling/sample selection and Identification ............................................................ 23 3.3. Research Tools and instruments ................................................................................. 24 3.4. Procedures ................................................................................................................... 24 3.4.1. Elemental and mineralogy analysis ................................................................ 25 a. Aqua regia digestion .............................................................................................. 26 b. Multi/Four acids digestions. ................................................................................... 27 c. ALS Multi-elements analysis procedure ................................................................ 27 3.4.2. Gold particle size distribution (PSD) ................................................................... 27 3.4.3. Fire assaying ........................................................................................................ 28 iii 3.4.5. Cyanide leaching .................................................................................................. 31 3.5. Data analysis ............................................................................................................... 31 Chapter 4. Results and Discussions ....................................................................................... 34 4.1. Results .................................................................................................................... 34 4.1.1. Problematic elements identification, quantification and evaluation of their effects. 34 4.1.2. Gold particle size distribution in samples ...................................................... 40 4.1.3. Analytical techniques for gold analysis ......................................................... 40 4.2. Discussions ............................................................................................................ 50 Chapter 5. Conclusions and Recommendations ..................................................................... 57 6. References .......................................................................................................................... 60 7. Appendix ............................................................................................................................ 68 Appendix A: Quality controls and quality assurance ......................................................... 68 Appendix B: Samples Information .................................................................................... 71 Appendix C: F Table ......................................................................................................... 72 Appendix D: t- distribution table ....................................................................................... 73 Appendix E: Comparing the gold assays obtained using six different analytical techniques .......................................................................................................................... 74 iv List of tables Table 1: Effects of elements on cupellation. .............................................................. 14 Table 2: Research tools and instruments .................................................................... 24 Table 3: Effect of elements on gold cyanide leaching. .............................................. 35 Table 4: Brittle buttons and scoriers on the cupels due to presence iron, sulphur and copper ......................................................................................................................... 39 Table 5: Comparison of gold cyanide leaching using Leachwell and without Leachwell. .................................................................................................................. 45 v List of figures Figure 1: (a) sheeted magnetite-pyrrhotite-carbonate vein in the Otjikoto deposit, (b) High temperature garnet-pyrrhotite vein and (c) microscopic image of pyrite- magnetite concentrated in a vein. ................................................................................. 5 Figure 2: (a) Pyrite-calcite-magnetite brittle vein, (b and C) Normal and microscopic image of coarse grained pyrite-calcite-magnetite vein. ............................................... 6 Figure 3: Project design flow chart. ..........................................................................