Investigation of old waste dump composition of lean gold-bearing ores from the Golden Pride Project (GPP) mining operation in Nzega district, Tanzania

The search for alternative sources of useful minerals is a pressing issue. One such possible source is the processing of lean gold-bearing ores, which previously did not seem feasible to exploit for subsoil users, leading to their disposal in off-balance ore dumps. Processing these resources becomes economically viable as gold prices rise and processing technologies improve over time. This paper presents the elemental and mineralogical composition of lean gold-bearing ore dumps from the Golden Pride Project (GPP) mining operation in Tanzania’s Lihendo district. This area contains an old dump of lean gold-bearing ores, weighing approximately 1.4 million tons. Extracting valuable components from lean mineral raw materials is a current priority. Sampling was conducted to study the dumps. Boreholes were drilled to a depth of 1 m, covering a total sampling area of 20 ha; 18 samples, each averaging 3 kg in weight, were collected. The results of X-ray fluorescence analysis (XRF) indicated the presence of Fe, S, Si, Ca, Ca, Mn, Cu, Al, Cr, Ti, As, and Ag in the collected samples. X-ray diffraction (XRD) analysis revealed that the main minerals in the dumps are muscovite, kaolinite, quartz, montimorillonite, and goethite. The average gold grade in the selected samples is 0.72 g/t. Studies of the grain-size distribution and gold distribution by grain-size classes after ore grinding demonstrated that the majority of gold (74%) is in the −75 μm class. In the initial mineral material of the dumps, the share of the +30-50 mm grain-size class is 81%. The paper proposes potential methods for processing lean dumps of gold-bearing ores. One such methods involves crushing the dump material, separating the −75 μm class, and subjecting it to direct leaching or leaching using “carbon-in-pulp” technique. Heap leaching appears to be the most promising method for extracting gold from such dumps in terms of technical and economic feasibility. Positive experience has been reported in applying this process to ores of similar mineralogical type.

1. Araya N., Kraslawski A., Cisternas L.A. Towards mine tailings valorization: Recovery of critical materials from Chilean mine tailings. Journal of Cleaner Production. 2020;263:121555. https://doi.org/10.1016/j.jclepro.2020.121555

2. Hlabangana N., Bhebhe S., Mguni N.G., et al. Optimisation of the leaching parameters of a gold ore in sodium cyanide solution. International Journal of Engineering Research and Reviews. 2018;6(1):1–10.

3. Tilton J.E. Is mineral depletion a threat to sustainable mining? SEG Newsletter. 2010. URL: http://inside.mines.edu/UserFiles/File/economicsBusiness/Tilton/Sustainable_Mining_Paper.pdf [Accessed: January 2023].

4. Nieto A., Muncher B. An applied economic assessment and value maximization of a mining operation based on an iterative cut-off grade optimization algorithm. International Journal of Mining and Mineral Engineering. 2021;12(4):309–326. https://doi.org/10.1504/IJMME.2021.121330

5. Aleksandrova T.N. Сomplex and deep processing of mineral raw materials of natural and technogenic origin: state and prospects. Journal of Mining Institute. 2022;256:503–504.

6. Marsden J.O. Overview of gold processing techniques around the world. Mining, Metallurgy & Exploration. 2006;23(3):121–125. https://doi.org/10.1007/BF03403198

7. Gorain B., Lakshmanan V.I., Ojaghi A. Ore body knowledge. In: Lakshmanan V., Gorain B. (eds.) Innovations and Breakthroughs in the Gold and Silver Industries: Concepts, Applications and Future Trends. NY: Springer International Publishing; 2019. https://doi.org/10.1007/978-3-030-32549-7_2

8. Baum W. Ore characterization, process mineralogy and lab automation a roadmap for future mining. Minerals Engineering. 2014;60:69–73. https://doi.org/10.1016/j.mineng.2013.11.008

9. Nayak A., Ashrit S., Jena M.S., et al. Mineralogical characterization for selection of possible beneficiation route for low-grade lead-zinc ore of Rampura Agucha, India. Transactions of the Indian Institute of Metals. 2020;73(3):775–784. https://doi.org/10.1007/s12666-020-01887-y

10. Asad M.W.A. Cutoff grade optimization algorithm with stockpiling option for open pit mining operations of two economic minerals. International Journal of Surface Mining, Reclamation and Environment. 2005;19(3):176–187. https://doi.org/10.1080/13895260500258661

11. Azimi Y., Osanloo M., Esfahanipour A. An uncertainty based multi-criteria ranking system for open pit mining cut-off grade strategy selection. Resources Policy. 2013;38(2):212–223. https://doi.org/10.1016/j.resourpol.2013.01.004

12. Kalitenge D. Cut-off Grade Optimization in Open-pit Mines Considering Two Processing Streams and Rehabilitation Cost. [Master of Science Thesis]. 2021. URL: https://era.library.ualberta.ca/items/0edd2e0d-a615-4243-9cbc-f8e1b2dde87e/download/601fca24-42e9-4b65-8215-320d35dd8695 [Accessed: October 2023]

13. Kondos P.D., Deschênes G., Morrison R.M. Process optimization studies in gold cyanidation. Hydrometallurgy. 1995;39(1–3):235–250. https://doi.org/10.1016/0304-386x(95)00032-c

14. Coetzee L.L., Theron S.J., Martin G.J., et al. Modern gold deportments and its application to industry. Minerals Engineering. 2011;24(6):565–575. https://doi.org/10.1016/j.mineng.2010.09.001

15. Dadgar A. Refractory concentrate gold leaching: Cyanide vs. bromine. The Journal of the Minerals, Metals & Materials Society. 1989;41(12):37–41. https://doi.org/10.1007/BF03220846

16. Mwanga A. The design of a mobile concentrator plant for gold extraction from Tailings in Tanzania. 2010. URL: https://www.academia.edu/en/71531220/The_design_of_a_mobile_concentrator_plant_for_gold_extraction_form_tailings_in_Tanzania [Accessed: January 2023].

17. Rasskazova A.V. Leaching of base gold-bearing ore with chloride-hypochlorite solutions. In: IMPC 2018 – 29th International Mineral Processing Congress. Moscow, September 17–21, 2018. Canadian Institute of Mining, Metallurgy and Petroleum; 2019. Pp. 4093–4098.

18. Gudkov S.S., Dementyev V.E., Druzhina G.Ya. Heap leaching of gold and silver. Irkutsk: JSC Irgiredmet; 2004. 352 p. (In Russ.)

19. Marsen J.O., House C.I. The chemistry of gold extraction. House Ellis-Horwood: Chichester; 1992.