Satellite and UAV monitoring of legacy mine sites via secondary iron mineral proxies. Case studies from the Republic of Cyprus and Australia

Challenge 

While recycling and alternative technologies show promise in reducing reliance on primary raw materials, the direct acquisition of essential metals and minerals depends on extracting new resources. The increasing demand for these resources has significant implications for mining, mineral processing, and environmental impact. Failing to effectively manage this demand for raw materials and mitigate the environmental impact of mining could impede global progress towards a cleaner energy future. The M4Mining project aims to promote sustainable mining practices using integrated remote sensing data to help monitor these operations. Its primary objective is to develop comprehensive remote sensing solutions for mining and tailings sites. This abstract introduces the identification of secondary iron minerals as proxies for estimating possible acid mine drainage (AMD) occurrence in legacy mine sites in both Cyprus and Australia.

Methodology 

Hyperspectral data of the secondary iron minerals hematite, goethite, limonite (goethite + lepidocrocite), jarosite and copiapite were collected in a laboratory setting to develop a method to separate secondary iron minerals from other minerals. Filtering by threshold of various indices, NDVI, ferric iron index, and iron feature band ratio, were best suited for this purpose. After filtering, the remaining pixels of the secondary iron minerals were predicted using a random forest (RF) classifier-model. It was possible to distinguish between the mineral classes hematite, goethite/ lepidocrocite and jarosite with over 93% area adjusted overall accuracy using 30 random control pixels for both sensors.

Results 

The first case study is applied is the Cu-Au-Pyrite mine Skouriotissa in the Republic of Cyprus. A spectral resampling from the hyperspectral laboratory data to Sentinel-2 (S2) and WorldView-3 (WV3) spectral resolution made it possible to adjust the hyperspectral method and provide results for both satellite sensors. Comparing the resulting maps show differences of minerals mapped on the surface likely due to the sensor’s different spatial resolution (S2 20m vs WV3 3.7m pixel). 

The M4Mining partners completed their first field survey in North-Western Queensland at the Mary Kathleen legacy mine site in September 2023. The former Uranium (U) open pit mine was active until 1982 and rehabilitated in 1985. The area was surveyed via UAV-borne hyperspectral data collection and satellite-borne hyperspectral (EnMap) instruments to assess the site's rehabilitation status. The method tested in the Republic of Cyprus is being applied to the Mary Kathleen site to evaluate surface oxidation processes that could indicate acid pH environments. A special focus is set on the gradient between the capped evaporation pond and the surrounding environment including the discharge area from the former pond. Different standard hyperspectral and multispectral algorithms are used to map the spatial distribution of iron oxides and evaporates. Although a final evaluation of the rehabilitation of the area is outside the scope of this study, the data collected intend to add valuable information to the continued monitoring of the site. 

Preliminary results from Australia will be provided for relative surface changes as indicators for processes occuring under the capped evaporation pond.