Hyperspectral REE (Rare Earth Element) Mapping of Outcrops—Applications for Neodymium Detection

Abstract

Abstract:In this study, an in situ application for identifying neodymium (Nd) enriched surface materials that uses multitemporal hyperspectral images is presented (HySpex sensor). Because of the narrow shape and shallow absorption depth of the neodymium absorption feature, a method was developed for enhancing and extracting the necessary information for neodymium from image spectra, even under illumination conditions that are not optimal. For this purpose, the two following approaches were developed: (1) reducing noise and analyzing changing illumination conditions by averaging multitemporal image scenes and (2) enhancing the depth of the desired absorption band by deconvolving every image spectrum with a Gaussian curve while the rest of the spectrum remains unchanged (Richardson-Lucy deconvolution). To evaluate these findings, nine field samples from the Fen complex in Norway were analyzed using handheld X-ray fluorescence devices and by conducting detailed laboratory-based geochemical rare earth element determinations. The result is a qualitative outcrop map that highlights zones that are enriched in neodymium. To reduce the influences of non-optimal illumination, particularly at the studied site, a OPEN ACCESSRemote Sens. 2015, 7 5161 minimum of seven single acquisitions is required. Sharpening the neodymium absorption band allows for robust mapping, even at the outer zones of enrichment. From the geochemical investigations, we found that iron oxides decrease the applicability of the method. However, iron-related absorption bands can be used as secondary indicators for sulfidic ore zones that are mainly enriched with rare earth elements. In summary, we found that hyperspectral spectroscopy is a noninvasive, fast and cost-saving method for determining neodymium at outcrop surfaces.

Reflectance Spectroscopy Characteristics of Turquoise

“…Hyper-spectral imaging has been widely used in geological mapping [8][9][10][11], ore exploration [12][13][14], nature conservation [15][16][17][18], and food or drink quality analysis [19,20]. Recent studies have also used this technology to conveniently and economically examine ancient documents and archaeological artifacts [21][22][23].…”

Remote Sensing Exploration of Nb-Ta-LREE-Enriched Carbonatite (Epembe/Namibia)

“…Limitations due to sub-economic REE enrichment at Epembe (∼0.5% TREO+Y) and high detection limits (e.g., for Nd 3+ ∼ 300 ppm in laboratory data [11]) were circumvented by the use of indicator minerals (e.g., see Mackay et al [22] or Bull [23]), like apatite or a specific type of pyroxene (e.g., aegirine or augite), to estimate the Nb-Ta-REE potential of the deposit. Those low REE abundances also disable the use of deconvolution algorithms, as proposed by Neave et al [17] or Boesche et al [16]. The indicator mineral approach, however, cannot be generalized to all carbonatites, but a similar approach as presented here is advised.…”

“…Expert knowledge is often required to get reliable results if the target is rather small [9,10]. However, applications of remote sensing for the exploration of carbonatite were only tested in a few studies ( [9,[11][12][13][14][15][16][17]). Thus, there is a need to improve remote sensing exploration techniques for REEs, Nb and Ta due to an increasing demand during the past few decades and the acceleration of this demand due to their augmenting use in high-tech industry ( [18,19]).…”

Survey of Hyperspectral Earth Observation Applications from Space in the Sentinel-2 Context

“…Geological classification not only depends on the SNR sensor characteristics, but also on the image conditions of acquisition (i.e., sun illumination, concentration levels of minerals, extend of minerals, season, exposition of the geology) [7,112,113]. Hyperion capacity for mine waste monitoring was evaluated by Mielke et al [114].…”