Mapping Co-Cr-Cu and Fe Occurrence in a Legacy Mining Waste Using Geochemistry and Satellite Imagery Analyses

Abandoned mining wastes are both an environmental challenge and a possible secondary raw material source. The characterization and monitoring of these sites are often expensive and cumbersome because of the need of repeated field surveys. Remote sensing data are a cost-effective alternative that helps in producing multiscale maps of mining wastes. These maps can be used to investigate and monitor the spatial patterns of different elements within the mining wastes. In this work, Sentinel-2 images are combined with the geochemical samples in order to map the distribution of iron, copper, chromium, and cobalt. The target area was the Vigonzano mining wastes in Northern Apennines (Italy) where there are a small number of geochemical analyses but a large amount of satellite image data. We used the multivariate geostatistical estimation method (Co-Kriging) that exploit the meaningful spatial correlation between the elements of interest and band ratios (obtained from Sentinel-2 images). The concentration maps highlighted subareas for Cu and Cr with an estimated grade of about 0.3% and 0.2%, respectively. In addition, the critical element Co showed an enrichment in the south-east part of the mining wastes, in a similar pattern as Cr. Instead, the obtained maps show Ce, La, Rb, and Nb depletion compared to the surrounding agricultural areas. The concentration maps were intended as a prefeasibility study to determine enriched areas for further detailed investigation

Detecting Lithium (Li) Mineralizations from Space: Current Research and Future Perspectives

Optical and thermal remote sensing data have been an important tool in geological exploration for certain deposit types. However, the present economic and technological advances demand the adaptation of the remote sensing data and image processing techniques to the exploration of other raw materials like lithium (Li). A bibliometric analysis, using a systematic review approach, was made to understand the recent interest in the application of remote sensing methods in Li exploration. A review of the application studies and developments in this field was also made. Throughout the paper, the addressed topics include: (i) achievements made in Li exploration using remote sensing methods; (ii) the main weaknesses of the approaches; (iii) how to overcome these difficulties; and (iv) the expected research perspectives. We expect that the number of studies concerning this topic will increase in the near future and that remote sensing will become an integrated and fundamental tool in Li exploration

Orogenic Gold in Transpression and Transtension Zones: Field and Remote Sensing Studies of the Barramiya–Mueilha Sector, Egypt

Multi-sensor satellite imagery data promote fast, cost-efficient regional geological mapping that constantly forms a criterion for successful gold exploration programs in harsh and inaccessible regions. The Barramiya–Mueilha sector in the Central Eastern Desert of Egypt contains several occurrences of shear/fault-associated gold-bearing quartz veins with consistently simple mineralogy and narrow hydrothermal alteration haloes. Gold-quartz veins and zones of carbonate alteration and listvenitization are widespread along the ENE–WSW Barramiya–Um Salatit and Dungash–Mueilha shear belts. These belts are characterized by heterogeneous shear fabrics and asymmetrical or overturned folds. Sentinel-1, Phased Array type L-band Synthetic Aperture Radar (PALSAR), Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER), and Sentinel-2 are used herein to explicate the regional structural control of gold mineralization in the Barramiya–Mueilha sector. Feature-oriented Principal Components Selection (FPCS) applied to polarized backscatter ratio images of Sentinel-1 and PALSAR datasets show appreciable capability in tracing along the strike of regional structures and identification of potential dilation loci. The principal component analysis (PCA), band combination and band ratioing techniques are applied to the multispectral ASTER and Sentinel-2 datasets for lithological and hydrothermal alteration mapping. Ophiolites, island arc rocks, and Fe-oxides/hydroxides (ferrugination) and carbonate alteration zones are discriminated by using the PCA technique. Results of the band ratioing technique showed gossan, carbonate, and hydroxyl mineral assemblages in ductile shear zones, whereas irregular ferrugination zones are locally identified in the brittle shear zones. Gold occurrences are confined to major zones of fold superimposition and transpression along flexural planes in the foliated ophiolite-island arc belts. In the granitoid-gabbroid terranes, gold-quartz veins are rather controlled by fault and brittle shear zones. The uneven distribution of gold occurrences coupled with the variable recrystallization of the auriferous quartz veins suggests multistage gold mineralization in the area. Analysis of the host structures assessed by the remote sensing results denotes vein formation spanning the time–space from early transpression to late orogen collapse during the protracted tectonic evolution of the belt

DAMSAT: An Eye in the Sky for Monitoring Tailings Dams

During the past decade, there have been a number of catastrophic tailings dam failures. Affordable monitoring systems, as well as methods to assess the risk posed to communities living downstream of these structures, are needed. In recent years the availability and accuracy of remote sensing information has increased, whilst its cost has decreased. This paper provides an overview of DAMSAT, a web-based system that brings together Earth observation and other data to help governments and mining companies monitor tailing dams, and estimate the downstream risks they pose. The methods developed are being piloted in Peru at a number of tailings dams, with the overall goal of improving the decision making process and sharing of information with respect to managing these structures. Engagement with Peruvian stakeholders has shown that DAMSAT provides tools that can help government authorities both reduce the risks and increase the sustainability of mining

Hyperspectral mapping of alteration minerals in the Pedra Branca gold deposit, Troia Massif, Ceará

Orientador: Carlos Roberto de Souza Filho, Mônica Mazzini PerrottaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de GeociênciasResumo: O depósito de ouro de Pedra Branca corresponde a uma descoberta recente realizada por projetos exploratórios privados na região do Maciço de Troia, setor setentrional da Província Borborema, região nordeste do Brasil. Compreende um depósito de ouro do tipo orogênico em fácies anfibolito, hospedado no greenstone belt paleoproterozoico da Serra das Pipocas. Imagens hiperespectrais aéreas (sistema sensor ProSpecTIR¿-VS) da região do depósito de ouro Pedra Branca, assim como dados espectroscópicos pontuais e de imageamento (instrumentos ASD-Fieldspec® e SisuCHEMA¿) tomados de amostras de rocha representativas da área, foram utilizados nesta pesquisa com intuito de investigar padrões espectro-mineralógicos em associações minerais de alteração, em escalas de alvo exploratório e de depósito. Os dados de espectroscopia foram integrados com informações geológicas do depósito e também com resultados de difração de raios-X e de análises petrográficas, com objetivo de identificar tendências minerais e físico-químicas nos padrões de alteração, que possam ser úteis como guias prospectivos para a região. Os resultados indicam a ocorrência de uma assembleia de alteração hidrotermal principal, cálcio-silicatada, em rochas hospedeiras ferromagnesianas, consistente com assembleia de alteração típica de zona proximal em depósitos de ouro orogênico em fácies anfibolito. Tendências composicionais nas micas brancas sugerem a ocorrência de uma fase de alteração hidrotermal posterior, a qual afetou as assembleias minerais preexistentes e cristalizou micas brancas ricas em Al em zonas estéreis e micas brancas pobres em Al em zona mineralizada. Análises espectroscópicas de amostras de afloramentos da área indicam que caulinitas bem cristalizadas e com substituição de Fe ocorrem como produto de alteração intempérica em amostras que contêm micas brancas pobres em Al e, portanto, poderiam configurar um guia prospectivo indireto para a mineralização, em escala de depósito. Os mapas minerais produzidos a partir do processamento das imagens hiperespectrais aéreas, combinados a resultados de geoquímica prospectiva em solo, suportam a interpretação de que a caulinita bem cristalizada pode ser utilizada como um guia para zonas mineralizadas, em rochas ferromagnesianas intemperizadas. Áreas-alvo para a prospecção aurífera na região podem ser apontadas a partir dos dados hiperespectrais aéreos pela identificação de misturas espectrais de nontronita e caulinita bem cristalizada. As informações levantadas nesta pesquisa sobre o comportamento espectro-mineralógico das associações minerais relacionadas ao depósito de ouro de Pedra Branca, a partir de análises espectroscópicas conduzidas em variadas escalas de observação e abordagem, demonstram que a Espectroscopia de Reflectância e o Sensoriamento Remoto Hiperespectral são técnicas apropriadas à prospecção mineral em regiões de cobertura vegetal e perfil intempérico típicos de condições climáticas semiáridas. Os resultados obtidos aqui fundamentam dados de referência para exploração aurífera no greenstone belt da Serra das Pipocas e, possivelmente, para outros depósitos de ouro orogênico em fácies anfibolitoAbstract: The Pedra Branca gold deposit is a recent discovery conducted by private exploration projects in the Troia Massif of northern Borborema Province, Northeast Brazil. It comprises an amphibolite-facies orogenic gold deposit, hosted by the Paleoproterozoic Serra das Pipocas greenstone belt. Airborne hyperspectral images (ProSpecTIR¿-VS system) covering the Pedra Branca gold deposit, as well as point and imaging spectroscopic data (ASD-Fieldspec® and SisuCHEMA¿ instruments) from representative rock samples in the area were used in this study to investigate spectro-mineralogical patterns in alteration mineral associations, either in exploration target and deposit scales. The spectroscopic data were integrated with geological information and also X-ray powder diffraction and petrography results, in order to reveal mineralogical and physicochemical alteration footprints that could guide the gold exploration in the region. The results indicate the occurrence of a main hydrothermal calc-silicate alteration in ferromagnesian host rocks, consistent with the proximal alteration assemblage typically found in amphibolite-facies orogenic gold deposits. White mica compositional trends suggest a later hydrothermal alteration event, which affected the pre-existing mineral assemblages and crystallized Al-rich white mica in distal areas and Al-poor white mica in the ore zone. Spectroscopic analyses of outcrop samples indicate that well-ordered kaolinite with Fe substitution occurs as a weathering product of Al-poor white mica-bearing samples, and therefore could be used as a proxy to mineralization in deposit scale. Mineral maps produced by processing of airborne hyperspectral images, combined to soil geochemical anomalies, further supports the notion that well-ordered kaolinite can be used as a proxy to mineralization in weathered ferromagnesian host rocks. Target areas for gold exploration can be pointed out by airborne hyperspectral data based on the identification of spectral mixtures of nontronite and well-ordered kaolinite. The information provided by this study on the spectro-mineralogical patterns of mineral associations related to the Pedra Branca gold deposit, by means of multi-scale spectroscopic analyses, demonstrate that reflectance spectroscopy and hyperespectral remote sensing are appropriate techniques for mineral exploration under semi-arid type weathering profile and vegetation cover. The results obtained here comprise baselines for gold exploration in the Serra das Pipocas greenstone belt, and possibly to other amphibolite-facies orogenic gold depositsMestradoGeologia e Recursos NaturaisMestre em Geociência

Drone-based Integration of Hyperspectral Imaging and Magnetics for Mineral Exploration

The advent of unoccupied aerial systems (UAS) as disruptive technology has a lasting impact on remote sensing, geophysics and most geosciences. Small, lightweight, and low-cost UAS enable researchers and surveyors to acquire earth observation data in higher spatial and spectral resolution as compared to airborne and satellite data. UAS-based applications range from rapid topographic mapping using photogrammetric techniques to hyperspectral and geophysical measurements of surface and subsurface geology. UAS surveys contribute to identifying metal deposits, monitoring of mine sites and can reveal arising environmental issues associated with mining. Further, affordable UAS technology will boost exploration data availability and expertise in the global south. This thesis investigates the application of UAS-based multi-sensor data for mineral exploration, in particular the integration of hyperspectral imagers, magnetometers and digital cameras (covering the visible red, green, blue light spectrum). UAS-based research is maturing, however the aforementioned methods are not unified effectively. RGB-based photogrammetry is used to investigate topography and surface texture. Image spectrometers measure mineral-specific surface signatures. Magnetometers detect geomagnetic field changes caused by magnetic minerals at surface and depth. The integration of such UAS sensor-based methods in this thesis augments exploration potential with non-invasive, high-resolution, safe, rapid and practical survey methods. UAS-based surveying acquired, processed and integrated data from three distinct test sites. The sites are located in Finland (Fe-Ti-V at Otanmäki; apatite at Siilinjärvi) and Greenland (Ni-Cu-PGE at Qullissat, Disko Island) and were chosen as geologically diverse areas in subarctic to arctic environments. Restricted accessibility, unfavourable atmospheric conditions, dark rocks, debris and vegetation cover and low solar illumination were common features. While the topography in Finland was moderately flat, a steep landscape challenged the Greenland field work. These restraints meant that acquisitions varied from site to site and how data was integrated and interpreted is dependent on the commodity of interest. Iron-based spectral absorption and magnetic mineral response were detected using hyperspectral and magnetic surveying in Otanmäki. Multi-sensor-based image feature detection and classification combined with magnetic forward modelling enabled seamless geologic mapping in Siilinjärvi. Detailed magnetic inversion and multispectral photogrammetry led to the construction of a comprehensive 3D model of magmatic exploration targets in Greenland. Ground truth at different intensity was employed to verify UAS-based data interpretations during all case studies. Laboratory analysis was applied when deemed necessary to acquire geologic-mineralogic validation (e.g., X-ray diffraction and optical microscopy for mineral identification to establish lithologic domains, magnetic susceptibility measurements for subsurface modelling), for example for trace amounts of magnetite in carbonatite (Siilinjärvi) and native iron occurrence in basalt (Qullissat). Technical achievements were the integration of a multicopter-based prototype fluxgate-magnetometer data from different survey altitudes with ground truth, and a feasibility study with a high-speed multispectral image system for fixed-wing UAS. The employed case studies transfer the experiences made towards general recommendations for UAS application-based multi-sensor integration. This thesis highlights the feasibility of UAS-based surveying at target scale (1–50 km2) and solidifies versatile survey approaches for multi-sensor integration.Ziel dieser Arbeit war es, das Potenzial einer Drohnen-basierten Mineralexploration mit Multisensor-Datenintegration unter Verwendung optisch-spektroskopischer und magnetischer Methoden zu untersuchen, um u. a. übertragbare Arbeitsabläufe zu erstellen. Die untersuchte Literatur legt nahe, dass Drohnen-basierte Bildspektroskopie und magnetische Sensoren ein ausgereiftes technologisches Niveau erreichen und erhebliches Potenzial für die Anwendungsentwicklung bieten, aber es noch keine ausreichende Synergie von hyperspektralen und magnetischen Methoden gibt. Diese Arbeit umfasste drei Fallstudien, bei denen die Drohnengestützte Vermessung von geologischen Zielen in subarktischen bis arktischen Regionen angewendet wurde. Eine Kombination von Drohnen-Technologie mit RGB, Multi- und Hyperspektralkameras und Magnetometern ist vorteilhaft und schuf die Grundlage für eine integrierte Modellierung in den Fallstudien. Die Untersuchungen wurden in einem Gelände mit flacher und zerklüfteter Topografie, verdeckten Zielen und unter oft schlechten Lichtverhältnissen durchgeführt. Unter diesen Bedingungen war es das Ziel, die Anwendbarkeit von Drohnen-basierten Multisensordaten in verschiedenen Explorationsumgebungen zu bewerten. Hochauflösende Oberflächenbilder und Untergrundinformationen aus der Magnetik wurden fusioniert und gemeinsam interpretiert, dabei war eine selektive Gesteinsprobennahme und Analyse ein wesentlicher Bestandteil dieser Arbeit und für die Validierung notwendig. Für eine Eisenerzlagerstätte wurde eine einfache Ressourcenschätzung durchgeführt, indem Magnetik, bildspektroskopisch-basierte Indizes und 2D-Strukturinterpretation integriert wurden. Fotogrammetrische 3D-Modellierung, magnetisches forward-modelling und hyperspektrale Klassifizierungen wurden für eine Karbonatit-Intrusion angewendet, um einen kompletten Explorationsabschnitt zu erfassen. Eine Vektorinversion von magnetischen Daten von Disko Island, Grönland, wurden genutzt, um großräumige 3D-Modelle von undifferenzierten Erdrutschblöcken zu erstellen, sowie diese zu identifizieren und zu vermessen. Die integrierte spektrale und magnetische Kartierung in komplexen Gebieten verbesserte die Erkennungsrate und räumliche Auflösung von Erkundungszielen und reduzierte Zeit, Aufwand und benötigtes Probenmaterial für eine komplexe Interpretation. Der Prototyp einer Multispektralkamera, gebaut für eine Starrflügler-Drohne für die schnelle Vermessung, wurde entwickelt, erfolgreich getestet und zum Teil ausgewertet. Die vorgelegte Arbeit zeigt die Vorteile und Potenziale von Multisensor-Drohnen als praktisches, leichtes, sicheres, schnelles und komfortabel einsetzbares geowissenschaftliches Werkzeug, um digitale Modelle für präzise Rohstofferkundung und geologische Kartierung zu erstellen

Multispectral and Hyperspectral Remote Sensing Data for Mineral Exploration and Environmental Monitoring of Mined Areas

In recent decades, remote sensing technology has been incorporated in numerous mineral exploration projects in metallogenic provinces around the world. Multispectral and hyperspectral sensors play a significant role in affording unique data for mineral exploration and environmental hazard monitoring. This book covers the advances of remote sensing data processing algorithms in mineral exploration, and the technology can be used in monitoring and decision-making in relation to environmental mining hazard. This book presents state-of-the-art approaches on recent remote sensing and GIS-based mineral prospectivity modeling, offering excellent information to professional earth scientists, researchers, mineral exploration communities and mining companies

Sentinel-2 for Mapping Iron Absorption Feature Parameters

Iron is an indicator for soil fertility and the usability of an area for cultivating crops. Remote sensing is the only suitable tool for surveying large areas at a high temporal and spatial interval, yet a relative high spectral resolution is needed for mapping iron contents with reflectance data. Sentinel-2 has several bands that cover the 0.9 μm iron absorption feature, while space-borne sensors traditionally used for geologic remote sensing, like ASTER and Landsat, had only one band in this feature. In this paper, we introduce a curve-fitting technique for Sentinel-2 that approximates the iron absorption feature at a hyperspectral resolution. We test our technique on library spectra of different iron bearing minerals and we apply it to a Sentinel-2 image synthesized from an airborne hyperspectral dataset. Our method finds the wavelength position of maximum absorption and absolute absorption depth for minerals Beryl, Bronzite, Goethite, Jarosite and Hematite. Sentinel-2 offers information on the 0.9 μm absorption feature that until now was reserved for hyperspectral instruments. Being a satellite mission, this information comes at a lower spatial resolution than airborne hyperspectral data, but with a large spatial coverage and frequent revisit time

Sentinel-2 for mapping iron absorption feature parameters

Iron is an indicator for soil fertility and the usability of an area for cultivating crops. Remote sensing is the only suitable tool for surveying large areas at a high temporal and spatial interval, yet a relative high spectral resolution is needed for mapping iron contents with reflectance data. Sentinel-2 has several bands that cover the 0.9 μm iron absorption feature, while space-borne sensors traditionally used for geologic remote sensing, like ASTER and Landsat, had only one band in this feature. In this paper, we introduce a curve-fitting technique for Sentinel-2 that approximates the iron absorption feature at a hyperspectral resolution. We test our technique on library spectra of different iron bearing minerals and we apply it to a Sentinel-2 image synthesized from an airborne hyperspectral dataset. Our method finds the wavelength position of maximum absorption and absolute absorption depth for minerals Beryl, Bronzite, Goethite, Jarosite and Hematite. Sentinel-2 offers information on the 0.9 μm absorption feature that until now was reserved for hyperspectral instruments. Being a satellite mission, this information comes at a lower spatial resolution than airborne hyperspectral data, but with a large spatial coverage and frequent revisit time