Integration of advanced remote sensing and geospatial methodologies to enhance mineral exploration: An example from the southern Gawler Ranges, South Australia

The world’s demand for metals is increasing and there is a growing need for mineral explorers to locate new ore deposits. Globally, discovery of economic mineral deposits is becoming more challenging due to the increasing depths where exploration is being conducted to discover mineral deposits. Most surficial deposits have been discovered, driving exploration into terrains with substantial weathered regolith cover, and requiring new exploration methods. Current traditional exploration methods including geophysics, high density soil sampling and geochemical analysis can be expensive, time consuming and limited in geographic extent. Although remote sensing methods have been applied to regional-scale mineral exploration, there is potential for them to be used more fully in regions where regolith is a continuing challenge. The overarching aim of this multidisciplinary thesis is to develop methods that integrate forms of remote sensing and geospatial information to reduce the risk and cost of exploration in weathered terrains by identifying and mapping surface alteration related to buried mineralisation. The study area used to develop and test these methodologies was the southern Gawler Ranges, South Australia, a region prospective for gold, porphyry-copper and epithermal-silver mineralisation. This semi-arid environment is moderately vegetated with limited geological exposures. Most basement rocks are overlain by approximately 100 m of weathered cover materials presenting challenges for both exploration and remote sensing methods. The broad research aim was addressed through three more specific objectives: 1. Development of an objective regolith-landform map using geospatial data and a repeatable methodology that can be used to guide the early stages of exploration potential assessment; 2. Characterisation of surface expressions of alteration mineralogy and interpretation of landscape processes using airborne hyperspectral imagery and mineralogical data; and 3. Integration of surface geochemistry, mineralogy and regolith-landform mapping to understand and map surface signatures of potential buried mineralisation. An unsupervised classification was applied to geospatial data layers including a Digital Elevation Model, Topographic Position Index and potassium, thorium and uranium gamma-ray radiometrics. This was clustered to generate an objective regolith-landform map representing the main regolith-landform types. This map captured many of the features typically mapped by traditional regolith-landform mapping as assessed by a statistical goodness of fit measure. While not a replacement for the resource-intensive traditional regolith maps derived from extensive field work, this method used freely available geospatial data an objective, repeatable methodology to produce a map that has potential to increase understanding of the landscape and assist targeting of areas of alteration and mineralisation for more detailed exploration. Airborne hyperspectral imagery was analysed by Spectral Feature Fitting, matching image spectra to reference spectra to identify alteration mineralogy. X-ray diffraction was used to independently validate mineralogy present in the landscape providing insight into unclear spatial distributions of some minerals and confirming the presence of key alteration minerals. Landscape processes were interpreted by integrating the spatial distribution of minerals with the objective regolith-landform map. Advanced argillic and argillic alteration were identified in the study area, focused around an exposed alunite breccia at Nankivel Hill. The results placed the central topographic feature, Nankivel Hill, proximal to potential porphyry mineralisation, with Peterlumbo Hill distal to mineralisation as possible chloritic alteration expressed at the surface in this region. Definition of lithologies from major element geochemistry identified ten rock and cover sequence types within the study area. A region-specific pathfinder element suite was defined using interpretation and thresholds of the Nankivel and Peterlumbo Hill rock exposures. The mineral hosts of these pathfinder elements were proposed from interpretation of semi-quantitative X-ray diffraction to determine the influence of weathering on dispersion of pathfinder elements from rock exposure to cover sequence materials. This suggested that most pathfinder elements were hosted in a variety of minerals including alunite, jarosite, microcline, muscovite, orthoclase and hematite in rock exposures and a broader range of feldspars, clays, micas, carbonates and iron oxides associated with cover sequence materials. Definitions of proximal and distal geochemical and mineralogical footprints of a porphyry deposit were delineated using the surface geochemistry, X-ray diffraction and hyperspectral mineralogical data. The landscape position of pathfinder elements was interpreted to recommend sample media with the most potential for identification of pathfinders at higher concentrations. The outcomes of this research demonstrate several encouraging approaches for use of land surface remote sensing and geospatial analysis in the context of mineral exploration in highly weathered and covered terrains. These methods can be integrated easily with more traditional methods and data to improve mineral exploration outcomes for the industry. The increasing need to explore terrains with extensive depths of cover in order to discover new ore deposits suggests that the industry would benefit from integrating these tools to enhance future exploration.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 202

Identification and Description of a Silicic Volcaniclastic Layer in Gale Crater, Mars, Using Active Neutron Interrogation

The Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, has been used to map a stratigraphically conformable layer of high‐SiO² material in Gale crater. Previous work has shown that this material contains tridymite, a high‐temperature/low‐pressure felsic mineral, interpreted to have a volcanic source rock. We describe several characteristics including orientation, extent, hydration, and geochemistry, consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession. Relationships with widely dispersed alteration features and orbital detections of hydrated SiO² suggest that this high‐SiO² layer extends at least 17 km laterally. Mineralogical abundances previously reported for this high‐SiO² material indicated that hydrous species were restricted to the amorphous (non‐crystalline) fraction, which is dominated by SiO². The low mean bulk hydration of this high‐SiO² layer (1.85 ± 0.13 wt.% water‐equivalent hydrogen) is consistent with silicic glass in addition to opal‐A and opal‐CT. Persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline SiO² has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted, despite having been transported in a fluviolacustrine system. Our results, including the conformable nature, large areal extent, and presence of volcanic glass, indicate that this high‐SiO² material is derived from the product of evolved magma on Mars. This is the first identification of a silicic volcaniclastic layer on another planet and has important implications for magma evolution mechanisms on single‐plate planets

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

On the progression of leaching from large particles in heaps

Includes bibliographical references.Although heap leaching is by now a well-established technology choice in the mining industry, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the successful application of heap leaching technology will ultimately depend on having a comprehensive understanding of the underlying fundamental processes for optimisation to take place...The subject of this research was, therefore, to understand more clearly the diffusion reaction phenomena of reagents through large particles and to provide true and reliable physical parameters to formulate the relevant modelling approaches to large particle leaching. A combination of standard optical microscopy, SEM, QEMSCAN and X-ray CT techniques has been used for the characterization of crack networks and mineral dissemination in the ore particles, which are important characteristics that determine the diffusion of reagents into and out of particles and the reactions within