Search Results (4)

Artisanal gold mining (AGM) activities are increasing globally and rely on rudimentary methods, such as amalgamation, to recover gold. In this study, mercury (Hg) metallurgical balances were conducted in 18 operations and gold (Au) balances in 35 operations, at a processing site serving approximately 4000 miners in the Korokpa mining area in Minna, Niger State, Nigeria. Ore processing involves grinding ore in hammer mills to below 1 mm, concentrating gold in sluice boxes, followed by amalgamating free gold particles in the concentrate. The results showed an average Au feed grade of 1.74 g/t and an average Au recovery from gravity concentration of 42.7%. Chemical analysis of the gravity separation tailing size fractions indicates that Au is lost in coarse fractions due to poor Au liberation and in fine fractions due to inefficiency in the sluicing process. Hg lost in the tailings was calculated as the mass balance difference between Hg added and the sum of Hg recovered through filtration and volatilized Hg in bonefires. It was found that 34% of Hg was lost during amalgamation, by volatilisation (18%) and with tailings (17%). The Hg lost-to-Au produced ratio was 2.6. By optimising procedures for grinding, classification, and concentration, the efficiency of recovery can be improved. Implementing a simple Hg recovery method, such as using a retort for condensation, and improving amalgam heating time can help miners minimise environmental loss. Full article

The objective of this work was to establish the gold and mercury losses in an artisanal mining deposit (Uke) in Nigeria to convince miners about their inefficiency and suggest changes in their gold extraction practices. Samples of feeds and tailings from five sluice box concentration processes previously ground in hammer mills below 1 mm (P80 = 0.5 mm) were systematically sampled every 15 min. for 4 h and sent for gold analyses by a fire assay and intensive cyanidation. Dry grain size analyses of primary and amalgamation tailings allowed us to find out in which size fraction gold and mercury are lost. Total mercury losses in sixteen operations were obtained by weighing mercury at the beginning and in all steps of the concentrates’ amalgamation. After analyses, the average gold grade in the feed resulted in 3.80 ± 1.52 ppm (two standard deviations). The gold recovery was 29.24 ± 13.24%, which is low due to a lack of liberation of the fine gold particles from the gangue (silicates). Finer grinding would be necessary. The mercury balance revealed that 42% of the mercury added is lost, in which 26% involves tailings and 16% evaporated. The Hg_Lost-to-Au_Produced ratio was found to be 3.35 ± 9.46, which is exceedingly high for this type of amalgamation process that should have this ratio around 1. One reason is the excessive amount of mercury in the amalgams, 76.5 ± 38.12%, when the normal is around 40%–50%. Mercury lost by evaporation in open bonfires is clearly contaminating amalgamation operators (usually children), neighbours, and the environment. The Hg-contaminated tailings and primary tailings are sold to local cyanidation plants, and this can form toxic soluble Hg(CN)₂ in the process. The results of this research were brought to the attention of the miners and other stakeholders, including the regulatory agencies of the government. The % gold recovery by amalgamation was not established in this study, but if this process recovers 50 to 60% of the liberated gold particles in a concentrate and 30% of gold was recovered in the sluice boxes, then the total gold recovery should be between 15 and 20; i.e., 80 to 85% of gold mined is lost. On average, an operation produces 8.26 g of gold/month, which is split to six miners, representing USD 69/month/miner or USD 2.3/day. It was discussed with miners, authorities, and community members (in particular female miners) how to avoid exposure to mercury, how to improve gold recovery without mercury, and the health and environmental effects of this pollutant. Full article

This work examines alluvial gold deposit mining and processing methods from the Argonautic expedition until the Renaissance. According to Greek mythology, the mountain rivers of Colchis (Georgia) carried coarse sand and gold particles, which were washed in special wooden sluice boxes. The finer fractions were held in the lower part of the device, which was lined with sheepskin. Using a sheepskin to extract gold from riverbeds gave rise to the myth of the Golden Fleece. Afterwards, during the Roman Empire period, the mining of alluvial gold was performed manually until the discovery of hydraulic mining, a technique that contributed to a massive increase in production. At the same time, the Romans employed various techniques to separate the metals from the total mass of the ore. Gold refining was carried out through cupellation and the mercury amalgamation process. During the Renaissance, Georgius Bauer Agricola wrote De Re Metallica, one of the essential machinery books in mining in the 16th century. He developed a new type of pump to remove water, the uncontrolled flow of which caused significant problems in the underground mining process. The bucket chain pump, the “pater noster” pump, and the piston pump are some of the most innovative devices he presented in his work. Also, Agricola extensively referenced the recovery techniques for gold and other precious metals during the Archaic period that helped preserve the myth of the Argonautic expedition and the Golden Fleece. Full article

The quantitative and qualitative assessment of gold grains from samples of glacial till is a well-established method for exploring gold deposits hidden under glaciated cover. This method, which is widely used in the industry and has resulted in numerous successes in locating gold deposits in glaciated terrain, is still based on artisanal gravity separation techniques and visual identification. However, being artisanal, it is limited by inconsistent recoveries and difficulties associated with visually identifying the predominantly small gold grains. These limitations hinder its capacity to decipher subtle or complex signals. To improve detection limits through the recovery of small gold grains, a new approach has recently been introduced into the industry, which is commercially referred to as the “ARTGold” procedure. This procedure involves the use of an optimized miniature sluice box coupled with an automated scanning electron microscopy routine. The capabilities of this improved method were highlighted in this study by comparing till surveys conducted around the Borden gold deposit (Ontario, Canada) using the conventional and improved methods at both local and regional scales. Relative to that with the conventional approach, the improved method increased the recovery of gold grains from samples (regional and down-ice mineralization) by almost one order of magnitude. (regional and down-ice mineralization), dominantly in regard of the small size fractions. Increasing the counts in low-abundance regional samples allows for a better discrimination between background signals and significant dispersions. The described method offers an alternative for improving the characterization of gold dispersal in glaciated terrain and related gold deposit footprints. Full article