Journal Article

Evolution of the Koma Bangou Gold Panning Site (Niger) From 1984 to 2020 Using Landsat Imagery

Kouamé, K. J., Baratoux, D., Yao, K. A., Baratoux, L., Abass Saley, A., Ahoussi, K. E.

2021

Overview

The severe drought of 1983–1984 in the Sahel region, and its socio‐economic impacts for people relying on farming had for consequence the first major gold rush at Koma Bangou in the southwestern part of Niger. Initiated in 1984, the gold panning activities were interrupted from 1989 to 1999 with exploration permits assigned to the mining industry. The site was reclassified at the year‐end 1999 as a gold panning site and artisanal mining resumed until present‐day. Gold panning activities such as ore extraction and cyanide processing produced mining waste including rocks, mine tailings, and treatment residues. Mining waste is a serious environmental, health and safety problem. Multispectral Landsat images (TM4‐5, ETM7+, OLI/TIRS) acquired between 1984 and 2020 were used to map the spatial evolution of waste generated by gold panning activities at Koma Bangou. Different processing methods were tested, including Minimum Noise Fraction (MNF) transform, Band Ratio (BR), and Feature Oriented Principal Component Selection (FPCS). The FPCS applied to hydroxyl‐bearing minerals appears to be most efficient to map gold extraction and cyanidation waste areas. The waste surface associated with ore extraction has increased from 9.43 ha in 1984 to 234.20 ha in 2020, with continuous expansion during the period of clandestine activity (1989–1999). The waste surface associated with cyanidation has increased from 5.56 ha in 2009 (the year of cyanide treatment introduction) to 99.53 ha in 2020. Landsat multispectral imagery proved a suitable data source for monitoring the evolution of gold mining waste and consequences of public policies at Koma Bangou. Plain Language Summary Artisanal gold mining in Niger is an alternative income‐generating activity for farmers. The first gold rush took place in Koma Bangou, in 1984, following the drought of 1983–1984 in order to cope with famine. The gold panning started in 1984, was interrupted during 1989–1999, and then resumed until present day. This work is based on multispectral analysis of almost 40 years of Landsat data to evaluate the evolution of the surface areas associated with gold extraction and cyanidation (cyanidation is a hydrometallurgical technique for extracting gold from ore by converting the gold to a water‐soluble coordination complex). Several image processing methods were tested for the purpose of mapping the extension of waste surfaces from 1984 onwards and the area of cyanidation waste from the year of introduction of this technique in 2009. Using the most efficient method, we report that the waste surface associated with gold extraction has increased from 9.43 ha in 1984 to 234.20 ha in 2020 with continuous expansion during the period of clandestine activity (1989–1999). The cyanidation areas have increased from 5.56 ha in 2009 to 99.53 ha in 2020. Key Points Koma Bangou is the major artisanal gold mining site in Niger and one of the major sites of artisanal gold mining in the Sahel Gold panning in Koma Bangou produces waste that degrades and pollutes the environment The use of Landsat satellite sensors allows to monitor the evolution of mining activities during four decades (1984–2020)

• Publisher: John Wiley & Sons, Inc,American Geophysical Union/Wiley,American Geophysical Union (AGU)
• Subject: Developing countries / Drought / Economic development / Economic impact / feature oriented principal component selection / GDP / Geology / Gold / Gold mines & mining / gold panning / Gross Domestic Product / Koma Bangou / Landsat / Landsat imagery / LDCs / Mine tailings / Mine wastes / Minerals / Public policy / Remote sensing / Sciences of the Universe / waste