Spatial distribution of artisanal goldmining in Ghana: Using machine
learning and Google Earth Engine to quantify conversion of vegetation to
gold mines
Abstract
Gold mining has played a significant role in Ghana’s economy for
centuries. Regulation of this industry has varied over time and while
large-scale mining is prevalent in the country, prevalence of artisanal
mining, or Galamsey has escalated throughout Ghana in recent
years. These mines are not only harmful to human health due to the use
of Mercury in the amalgamation process, but also leave a significant
footprint on terrestrial ecosystems, degrading and destroying forested
ecosystems in the region. This study used machine learning and Google
Earth Engine to quantify the footprint of artisanal gold mines in Ghana
and understand how conversion of forested regions to mining has changed
from 2002-2019. We used Landsat imagery and a random forest
classification to classify areas of anomalous NDVI loss during this time
period and used WorldView image collections to assess the accuracy of
the model. We then used a 3-year moving average to calculate the year of
maximum derivative NDVI values. We used this calculation to identify the
year of conversion to mining. Within the study area of Southwestern
Ghana, our analysis showed that approximately 35,000 ha of vegetation
were converted to mining. The majority of this mining occurred between
2014 and 2017. Additionally, around 700 ha ha of mining occurred within
protected areas defined by the World Database on Protected Areas. Often,
artisanal mining appears to be co-located with rivers such as the Orin
and Ankobra Rivers, demonstrating the potential of these mines to affect
access to clean drinking water. Through the process of gold extraction,
these mines leave a distinct footprint with a series of ponds following
these major rivers. However, while the footprints of these ponds are
spatially distinct, our model does not distinguish between active and
inactive ponds if no remediation actions are taken following inactivity.
Future research should work towards distinguishing between active and
inactive mining sites to better understand current levels of mining
activity in Ghana.