The synergistic use of multi-scale remote sensing data for the identification of hydrothermal alteration patterns in Los Frailes, Spain

Abstract

• FieldSpec4, SisuROCK, AisaFenix and WorldView-3 results are used synergistically. • Spectral data characterise hydrothermal alterations typical for massive sulphides. • Chlorite and white mica mapping results coincide mostly between the data scales. • Mapping discrepancies are explained by different data types and analysis methods. • Multi-scale spectral data can help to identify potential exploration targets. Remote sensing data can be successfully applied in mineral resource prospecting and exploration. With the increasing number of remote sensing sensors and methods, the application of multi-scale remote sensing data has met a broad audience in the geological remote sensing community over the last few years. Multi-scale remote sensing data close the scale gap between distal (satellite) and proximal (laboratory) remote sensing data, offering both a general and detailed overview of the target and allowing a synergistic use. In this study, the volcano-sedimentary hosted massive sulphide ore deposit Los Frailes in the east of the Iberian Pyrite Belt (IPB) in Spain is investigated for the first time with multi-scale remote sensing techniques. A typical hydrothermal alteration zonation is associated to the massive sulphide ore body in Los Frailes, which is characterised by an inner chlorite-rich zonation showing a strong Fe-enrichment and a peripheral muscovite-rich zonation, which is moderately enriched in Fe. The characterisation of these zones support traditional mineral exploration techniques especially in the prospecting phase by detecting regions of interest, thereby reducing time and cost consumption. By evaluating the synergistic use of multi-scale remote sensing data for massive sulphide exploration, an enhanced application for the economic prospecting and exploration of mineral resources in Los Frailes is introduced. Optical data are used for the detection, identification and characterisation of chlorite and white mica occurrences and compositions. A drill core is analysed with the FieldSpec4 Hi-res hyperspectral point spectrometer. Rock samples are investigated in the laboratory using the SisuROCK hyperspectral core imaging station. AisaFENIX hyperspectral field-based and WorldView-3 multispectral satellite data of the open pit are analysed. The mineral(-group) identification and characterisation are performed with either spectral feature fitting methods (hyperspectral) or mineral indices (multispectral). Hyperspectral analyses show Mg-/Al-substitutions due to Fe-enrichment owing to wavelength shifts of the absorption maximum in chlorite and white mica, respectively. The identification and characterisation of the Fe-OH absorption feature of chlorite at around 2250 nm is more challenging compared to the Al-OH absorption feature of muscovite at around 2200 nm because the spectral signature is more subtle regarding the depth and width. However, the chloritic hydrothermal alteration zonation in the footwall is successfully detected in all scales. The hydrothermal muscovite-rich zonation in the footwall is barely outcropping in the pit and is not captured in the drill core. However, the muscovite-rich alteration zonation in the hanging wall is indicated in all scales. Discrepancies in the results arise mainly from different spectral and spatial resolutions of the sensors and differing data acquirement conditions, such as different surface exposures, viewing angles and illumination conditions. The results show that the multi-scale method offers great opportunities to localise potential prospecting and exploration targets in the Iberian Pyrite Belt. The synergistic use of the different remote sensing scales offers a complete picture of the target by gaining macroscopic to regional spectral information collectively, which is superior to using only one scale. The method is relatively fast and cost-effective, which makes the identification of potential exploration targets more efficient.