Recovering the lost gold of the developing world: case study in Migori County, Kenya

Mitchell, C.J. ORCID: https://orcid.org/0000-0002-5911-5668; Bide, T.; Odhiambo, C.. 2023 Recovering the lost gold of the developing world: case study in Migori County, Kenya. In: Wardrop, D., (ed.) Proceedings of the 22nd Extractive Industry Geology Conference 2022 and technical meeting 2023. Extractive Industry Geology, 98-104.

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Abstract/Summary

Artisanal & Small-scale Gold Mining (ASGM) is a subsistence level livelihood for many rural communities across the world. In Kenya it provides work for an estimated 40,000 people and produces 5 Tonnes of gold per year. The impact of ASGM is double-edged with the economic benefits offset by damage to the environment and the health of the mining communities due to the widespread use of mercury to recover gold. As a signatory to the Minamata Convention on Mercury (2017), Kenya has agreed to eliminate the use of mercury, formalise the ASGM sector,introduce good practice and protect the health of mining communities. Migori County is a major ASGM centre in southwest Kenya where gold is produced from quartz–carbonate reefs in the Migori greenstone belt. Recovery of gold involves extraction of the ore by mining and processing. The deep mine shafts are unstable and there are regular reports of fatalities due to mine collapse. The gold is recovered by manual crushing, ball milling, sluice box concentration and mercury amalgamation. Residual gold is recovered by cyanidation of the tailings. The local ASGM communities are concerned about the safety of the mining, the environmental impact of mercury and poor gold recovery. The British Geological Survey (BGS) worked with the University of Nairobi and the Migori County Artisanal Miners Co-operative (MICA) to promote good ASGM practice, reduce mercury use and improve gold recovery using appropriate technology. On average hard rock gold is finer than 100 microns. This makes the use of a sluice box a very inefficient recovery method with expected recoveries as low as 20% for gold of 100 microns or finer. This paper outlines preliminary good practice guidance for ASGM in Migori, Kenya. The guidance includes advice on sluice box design including the use of longer sluice channels (at least 3 metres or preferably more) and appropriate sluice box gradients; closed circuit milling; size classification and conditioning of the sluice box feed material; and alternative gravity processing methods to enhance gold recovery; and mercury recovery using retorts. This BGS research was part of the BGS Official Development Assistance (ODA) research project “From source to sink: Quantifying the local and downstream environmental impacts of ASGM”.

Item Type:	Publication - Book Section
Additional Keywords:	Gold, Mercury, Kenya, ASM, artisanal-scale mining
NORA Subject Terms:	Earth Sciences
Date made live:	12 Mar 2025 10:59 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538617

Item Type:

Publication - Book Section

Additional Keywords:

Gold, Mercury, Kenya, ASM, artisanal-scale mining

NORA Subject Terms:

Earth Sciences

Date made live:

12 Mar 2025 10:59 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/538617