Mapping Potentially Acid Generating Material on Abandoned Mine Lands Using Remotely Piloted Aerial Systems

Abstract

Weathering and transport of potentially acid generating material (PAGM) at abandoned mines can degrade downstream environments and contaminate water resources. Monitoring the thousands of abandoned mine lands (AMLs) for exposed PAGM using field surveys is time intensive. Here, we explore the use of Remotely Piloted Aerial Systems (RPASs) as a complementary remote sensing platform to map the spatial and temporal changes of PAGM across a mine waste rock pile on an AML. We focus on testing the ability of established supervised and unsupervised classification algorithms to map PAGM on imagery with very high spatial resolution, but low spectral sampling. At the Perry Canyon, NV, USA AML, we carried out six flights over a 29-month period, using a RPAS equipped with a 5-band multispectral sensor measuring in the visible to near infrared (400–1000 nm). We built six different 3 cm resolution orthorectified reflectance maps, and our tests using supervised and unsupervised classifications revealed benefits to each approach. Supervised classification schemes allowed accurate mapping of classes that lacked published spectral libraries, such as acid mine drainage (AMD) and efflorescent mineral salts (EMS). The unsupervised method produced similar maps of PAGM, as compared to supervised schemes, but with little user input. Our classified multi-temporal maps, validated with multiple field and lab-based methods, revealed persistent and slowly growing ‘hotspots’ of jarosite on the mine waste rock pile, whereas EMS exhibit more rapid fluctuations in extent. The mapping methods we detail for a RPAS carrying a broadband multispectral sensor can be applied extensively to AMLs. Our methods show promise to increase the spatial and temporal coverage of accurate maps critical for environmental monitoring and reclamation efforts over AMLs.

Monitoring sedimentary areas from mine waste products with Sentinel‐2 satellite images: A case study in theSEof Spain

“…Secondly, in the SAM classification, the strict threshold chosen might generate an underestimation of the affected surface (Shahriari et al, 2014). Finally, the colour composition depends on a subjective visual interpretation, and, therefore, is not suitable for a cross‐check with the soil land uses map (Cramer et al, 2021; Sabins, 1999), so it should be cautiously taken into consideration.…”

“…However, each of the remote sensing techniques applied has its own limitations. For instance, the choice of the break thresholds in the band ratios were derived from a literature review, which can generate uncertain results (Cramer et al, 2021; Sabins, 1999). Also, band ratios only allow a relative quantification of the iron oxides and hydroxyl‐bearing minerals.…”