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Field and drill core hyperspectral sensing technologies are cost-effective tools for identifying footprints of hydrothermal mineral systems, vectoring towards potential ore bodies and differentiating domains in ore deposits. Hyperspectral visible-near, shortwave and thermal infrared data were collected from drill core and chip samples from the Cu-Zn-Mo deposit of Antamina, Peru, to map the relative abundance and chemical composition of major gangue minerals, such as garnet and quartz. This study focuses on grandite-series garnets (i.e. grossular to andradite), which show distinct variations with regard to their relative abundance and chemical composition across the Antamina deposit. Reflectance spectra were calibrated with quantitative mineralogy derived from scanning electron microscopy and X-ray diffraction-derived mineralogy. This allowed the modal abundances of garnet and quartz to be modelled using a partial least squares approach, achieving regression coefficients of up to 0.887 and 0.891, respectively. The accuracy of the modelled modal mineral abundance depended on the method of external calibration, and the mineral assemblage associated with the mineral of interest. Comparing the hyperspectral data with major sulfide mineralogy, whole-rock geochemistry, electron probe microanalysis and Fourier-transform infrared microscopy allowed the identification of five ore clusters at Antamina, including high Cu ± Zn-Mo; Zn + Cu ± Mo and Zn ± Cu in the exoskarn and Mo ± Cu-Zn and high Mo ± Cu-Zn in the endoskarn. The garnet species comprise mainly grossular ± andradite in the endoskarn and andradite in the exoskarn. Different garnet compositions are associated with different sulfide mineral assemblages, making Antamina an ideal candidate for evaluating hyperspectral sensing for rapid and reliable mineral characterisation of skarn deposits. Vector minerals typical of skarn deposits (e.g. garnet, vesuvianite) were determined using this approach, indicating its potential for effectively characterising skarn deposits worldwide. [ABSTRACT FROM AUTHOR]

The integration of surface and subsurface geoscience data is critical for efficient and effective mineral exploration and mining. Publicly accessible data sets to evaluate the various geoscience analytical tools and their effectiveness for characterisation of mineral assemblages and lithologies or discrimination of ore from waste are however scarce. The open-access Rocklea Dome 3D Mineral Mapping Test Data Set (Laukamp, 2020; 10.25919/5ed83bf55be6a) provides an opportunity for evaluating proximal and remote sensing data, validated and calibrated by independent geochemical and mineralogical analyses, for exploration of channel iron deposits (CIDs) through cover. We present hyperspectral airborne, surface, and drill core reflectance spectra collected in the visible–near-infrared and shortwave infrared wavelength ranges (VNIR–SWIR; 350 to 2500 nm), as well as whole-rock geochemistry obtained by means of X-ray fluorescence analysis and loss-on-ignition measurements of drill core samples. The integration of surface with subsurface hyperspectral data collected in the frame of previously published Rocklea Dome 3D Mineral Mapping case studies demonstrated that about 30 % of exploration drill holes were sunk into barren ground and could have been of better use, located elsewhere, if airborne hyperspectral imagery had been consulted for drill hole planning. The remote mapping of transported Tertiary detritals (i.e. potential hosts of channel iron ore resources) versus weathered in situ Archaean bedrock (i.e. barren ground) has significant implications for other areas where "cover" (i.e. regolith and/or sediments covering bedrock hosting mineral deposits) hinders mineral exploration. Hyperspectral remote sensing represents a cost-effective method for regolith landform mapping required for planning drilling programmes. In the Rocklea Dome area, vegetation unmixing methods applied to airborne hyperspectral data, integrated with subsurface data, resulted in seamless mapping of ore zones from the weathered surface to the base of the CID – a concept that can be applied to other mineral exploration and mineral deposit studies. Furthermore, the associated, independent calibration data allowed the quantification of iron oxide phases and associated mineralogy from hyperspectral data. Using the Rocklea Dome data set, novel geostatistical clustering methods were applied to the drill core data sets for ore body domaining that introduced scientific rigour to a traditionally subjective procedure, resulting in reproducible objective domains that are critical for the mining process. Beyond the previously published case studies, the Rocklea Dome 3D Mineral Mapping Test Data Set has the potential to develop new methods for advanced resource characterisation and develop new applications that aid exploration for mineral deposits through cover. The white mica and chlorite abundance maps derived from airborne hyperspectral, presented here for the first time, highlight the additional applications of remote sensing for geological mapping and could help to evaluate newly launched hyper- and multispectral spaceborne systems for geoscience and mineral exploration. [ABSTRACT FROM AUTHOR]

The integration of surface and subsurface geoscience data is critical for efficient and effective mineral exploration and mining. Publicly accessible datasets to evaluate the various geoscience analytical tools and their effectiveness for characterisation of mineral assemblages and lithologies or discrimination of ore from waste are however scarce. The open access Rocklea Dome 3D Mineral Mapping Test Data Set (Laukamp, 2020; https://doi.org/10.25919/5ed83bf55be6a) provides an opportunity for evaluating proximal and remote sensing data, validated and calibrated by independent geochemical and mineralogical analyses, for exploration of channel-iron deposits (CID) through cover. We present hyperspectral airborne, surface and drill core reflectance spectra collected in the visible-near infrared and shortwave infrared wavelength ranges (VNIR-SWIR; 350 to 2500 nm), as well as whole rock geochemistry obtained by means of X-Ray fluorescence analysis and loss on ignition measurements of drill core samples. The integration of surface with subsurface hyperspectral data collected in the frame of previously published Rocklea Dome 3D Mineral Mapping case studies demonstrated that about 30 % of exploration drill holes were sunk into barren ground and could have been of better use, located elsewhere, if airborne hyperspectral imagery had been consulted for drill hole planning. The remote mapping of transported Tertiary detritals (i.e. potential hosts of channel iron ore resources) versus weathered in situ Archaean geology (i.e. barren ground) has significant implications for other areas where "cover" (i.e. regolith and/or sediments covering bedrock hosting mineral deposits) hinders mineral exploration. Hyperspectral remote sensing represents a cost-effective method for regolith landform mapping required for planning drilling programs. In the Rocklea Dome area, vegetation unmixing methods applied to airborne hyperspectral data, integrated with subsurface data, resulted in seamless mapping of ore zones from the weathered surface to the base of the CID - a concept that can be applied to other mineral exploration and mineral deposit studies. Furthermore, the associated, independent calibration data allowed to quantify iron oxide phases and associated mineralogy from hyperspectral data. Using the Rocklea Dome data set, novel geostatistical clustering methods were applied to the drill core data sets for ore body domaining that introduced scientific rigour to a traditionally subjective procedure, resulting in reproducible objective domains that are critical for the mining process. Beyond the already published case studies, the Rocklea Dome 3D Mineral Mapping Test Data Set has the potential to develop new methods for advanced resource characterisation and develop new applications that aid exploration for mineral deposits through cover. The here newly presented white mica and chlorite abundance maps derived from airborne hyperspectral highlight the additional applications of remote sensing for geological mapping and could help to evaluate newly launched hyper- and multispectral spaceborne systems for geoscience and mineral exploration. [ABSTRACT FROM AUTHOR]

Whole rock geochemical analysis of drill core is crucial for rock classification and understanding the evolution of a geological province. This becomes even more important when access to fresh rock samples is hindered by considerable overburden, such as in the case of the basement to the Eucla Basin sediments in Australia. A partial least squares (PLS) regression method was trialled to model geochemical indices, commonly applied for classification of igneous rocks, from hyperspectral visible-near infrared (VNIR; 350 to 1200 nm), shortwave infrared (SWIR; 1200 to 2500 nm) and thermal infrared (TIR; 6000 to 14,500 nm) reflectance spectra of three drill cores intersecting the basement of the Eucla Basin. Modelling of the Mg# (Mg/Mg + Fe) achieved a high correlation between the calculated and predicted values (i.e. R2 > 0.9) at an RMSE of about 10 %. The 2200 to 2400 nm wavelength region of the SWIR was key in modelling the Mg#, with amphibole and chlorite-related absorption features overlapping with the most important input bands in the PLS model. Modelling of the silicon, calcium, iron, magnesium index (SCFM; SiO 2 /(SiO 2 + CaO + FeO + MgO)) required the TIR wavelength range, where diagnostic spectral signatures of silicates are located. PLS-based modelling of the SCFM achieved even a high correlation (i.e. R2 > 0.8) when the model was developed for one drill core but applied to another drill core that intersects the same lithologies. The third geochemical index trialled was the aluminium saturation index (ASI; Al 2 O 3 /(Na 2 O + K 2 O + CaO), producing high correlation between calculated and predicted ASI when using either, the VNIR-SWIR and the TIR wavelength ranges as input. Our study demonstrates how PLS regression can utilise hyperspectral data to determine geochemical indices, without the cost of full geochemical analysis of every sample in a wide array of rock types. The higher spatial resolution of the modelled geochemistry and the extrapolation of the modelling results to intervals that haven't been sampled for geochemistry supports stratigraphic correlation between drill cores. Furthermore, the combined analysis of geochemical and hyperspectrally-derived mineralogy helps mapping the intensity of weathering of basement as well as mineralogical and physicochemical gradients potentially related to hydrothermal systems. • PLS-based modelling of geochemical indices from hyperspectral reflectance spectra • Correlations between calculated and modelled Mg#, SCFM and ASI are significant. • RMSE of modelled geochemical index values about 10 % on average • Comparison of input bands with reflectance spectra reveals causative relationships. • Modelling results can be used for stratigraphic correlations between drill cores. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The minerals exploration undercover relies on the understanding of the ore-forming processes and the associated alteration characteristics that are used in vectoring towards a deposit. Previously, the proposed process for forming the 1590 Ma Abra base-metal deposit, hosted at 250 m depth in the Paleoproterozoic Edmund Basin of the Western Australian Capricorn Orogen, was through exhalation to the seafloor (SEDEX-style). Lacking any visible signs of alteration, sediments overlying the Abra deposit were perceived as younger, unaltered, and cutting the mineralisation and associated alteration comprised of siderite, chlorite and minor sericite. However, a recent study delineated a phengitic (i.e. Al-poor, Mg-, Fe-, Si-rich) white mica footprint in regolith above the deposit from hyperspectral field and remote sensing data. This study links the surficial mineral footprint to the deposit below through detailed analysis of hyperspectral data from drill core. The hyperspectral data processing results were validated using optical microscopy, micro-XRF and SEM-EDS analysis, and compared with geochemical, lithological and structural drill core data. Hyperspectral short-wave infrared (SWIR) data revealed a vertically zoned alteration footprint from the deposit to the surface, where very fine-crystalline phengitic white mica (i.e. sericite) and chlorite are most abundant a few tens of metres above the deposit. The abundance of chlorite gradually decreases, and the distal phengitic alteration is cut by the present erosional surface, but only moderately affected by weathering, confirming the surficial footprint detected in the previous study. Similarly, a vertically zoned carbonate alteration was delineated from thermal infrared (TIR) reflectance spectra from drill cores up to 2 km away from the deposit. Carbonate alteration from proximal to distal comprised of Mn-rich siderite, ankerite and ferroan dolomite, which replace the dolomite matrix in coarse-grained stratigraphic sequences. The replacement of dolomite matrix suggests that these permeable horizons acted as fluid conduits, which channelled hydrothermal fluids into sedimentary strata from a feeder structure. The presence of a vertically zoned carbonate and chlorite-phengite footprint in the overlying sediments advocates for their deposition before the ore formation at Abra, and a sub-seafloor replacement within a permeable sedimentary sequence as the ore-forming process. Comparable alteration footprints have been described around some world-class sediment-hosted base-metal deposits, including the Sullivan in the British Columbia, which is considered as a classic SEDEX-style by some and an exhalative-replacement hybrid by others. Also, identical footprints are common around the volcanic-hosted massive sulphide and are associated with the carbonate replacement-style deposits – an overlap which is an interesting future research space where hyperspectral technologies could provide answers. Validated hyperspectral data combined with geochemical, lithological and structural information enabled the identification of a subtle mineral footprint above the Abra deposit, and the established method can be used for vectoring towards other buried mineralisations – even through weathering. [ABSTRACT FROM AUTHOR]

Abstract: Detailed hydrothermal alteration investigations, including petrography, infrared reflectance spectroscopy (IRS) and XRD of the low sulfidation epithermal Co–O mine, located in Eastern Mindanao (Philippines) revealed that both distal and intermediate hydrothermal alteration zones contain dominantly illite and chlorite, whereas the proximal alteration zone comprises mainly illite, chalcopyrite and pyrite. The gold-bearing veins and the proximal hydrothermal alteration zone display a distinct absence of K-rich hydrothermal alteration minerals such as K-feldspar (adularia). Gold mineralization in the Co–O mine is controlled by an extensive quartz-breccia vein system, which is characterized by three distinct stages of vein (incl. breccias) formation. Gold is mainly observed in stages 2 and 3 veins. Stage 1 veins appear as fragments in stage 2 veins and display boiling textures such as quartz pseudomophs after bladed calcite. These veins further display colloform to crustiform banding and contain pyrite, chalcopyrite and minor gold located in the colloform bands and between bladed quartz pseudomorphs. Stage 2 veins comprise mostly banded to massive quartz and contains sulfides parallel to bands or disseminated. These veins are fine-grained with mosaic/jigsaw quartz and contain calcite blebs and/or fragments of stage 1 veins. Gold is in textural equilibrium with chalcopyrite, sphalerite, and locally pyrite. Stage 3 veins consist of quartz and carbonate (locally Mn-rich), and display irregular banded and comb textures. In auriferous veins of this stage gold is in textural equilibrium with chalcopyrite and pyrite (with local abundance of sphalerite). Other sulfide minerals observed with gold in stages 2 and 3 are galena, acanthite and locally jalpaite. The XRD and IRS provide inconsistent results regarding the abundance of K-rich clays (e.g., illite) associated with auriferous veins. Illite, with possibly interlayered swelling clays, such as Al-smectite, was identified in auriferous vein stages 2 and 3 using IRS, but could not be confirmed by XRD. Comparative analysis of the results of these techniques with respect to the ordering of micaceous minerals, suggest less ordered white mica proximal to the veins. Vein textures such as banded quartz, the absence of K-feldspar and the abundance of illite (interlayered Al-smectite) suggest relatively low temperatures of formation of the hydrothermal alteration system and point to a potential boiling horizon located deeper or marginal to the currently exploited levels of the Co–O mine. The absence of K-feldspar may also be related to relatively low temperatures of the hydrothermal fluid, the medium potassium-rich magma series of the host rocks, and/or a relatively low oxidation state of the hydrothermal fluid. [Copyright &y& Elsevier]

Abstract: A simple quadratic method is proposed for estimating the wavelengths of absorption features in the short wave infrared spectral region from hyperspectral instruments ranging from 2 to 18nm sampling intervals. The method uses a direct substitution of the three spectral reflectance bands to achieve an estimate of the wavelength of the point of maximum absorption. The method is shown to be stable across different sampling regimes and therefore across different hyperspectral instruments. The results show it is possible to accurately estimate the wavelength of spectral absorption features to an RMSE of ±3.8nm in the 2000–2500nm spectral region over multiple sampling intervals and resolutions in sensors with signal-to-noise greater than 500:1. [Copyright &y& Elsevier]

Reflectance spectroscopy allows cost-effective and rapid mineral characterisation, addressing mineral exploration and mining challenges. Shortwave (SWIR), mid (MIR) and thermal (TIR) infrared reflectance spectra are collected in a wide range of environments and scales, with instrumentation ranging from spaceborne, airborne, field and drill core sensors to IR microscopy. However, interpretation of reflectance spectra is, due to the abundance of potential vibrational modes in mineral assemblages, non-trivial and requires a thorough understanding of the potential factors contributing to the reflectance spectra. In order to close the gap between understanding mineral-diagnostic absorption features and efficient interpretation of reflectance spectra, an up-to-date overview of major vibrational modes of rock-forming minerals in the SWIR, MIR and TIR is provided. A series of scripts are proposed that allow the extraction of the relative intensity or wavelength position of single absorption and other mineral-diagnostic features. Binary discrimination diagrams can assist in rapidly evaluating mineral assemblages, and relative abundance and chemical composition of key vector minerals, in hydrothermal ore deposits. The aim of this contribution is to make geologically relevant information more easily extractable from reflectance spectra, enabling the mineral resources and geoscience communities to realise the full potential of hyperspectral sensing technologies. [ABSTRACT FROM AUTHOR]

Remotely sensed hyperspectral datasets were integrated with petrographic data to map the distribution of sedimentary rocks in order to infer grain size variations within the siliciclastic, Paleoproterozoic Bresnahan Group in Western Australia. Finer sandstones have greater compositional variation compared to coarser sandstones, with higher modal proportions of mudstone intraclasts, K-feldspar, and muscovite laths, and lower modal quartz. Partial Least Squares modelling indicates a link between visible to shortwave infrared spectral data collected on samples and their average grain size. Specific electronic absorptions are important for defining this relationship, particularly in the blue-green visible spectra, wavelengths related to water or hydroxyl bonds, along with certain wavelengths in the shortwave infrared (SWIR) spectra. The results from field samples were compared to airborne hyperspectral datasets which showed broad scale regional variations in composition could be discerned from processed white mica abundance maps and images that use spectral bands 2350 nm and 2200 nm. The remotely sensed compositional variations are relatable to changes in sandstone grain size. Diagenetic alteration and surface weathering may influence the absorption spectra, although the effect of the latter can be reduced by using processed white mica abundance maps. Overall, the results show that airborne hyperspectral datasets, particularly the SWIR part of the spectra, can be useful to remotely map spatial compositional variations associated with sandstone grain size. This shows the method can be used to remotely map siliciclastic successions in other sedimentary basins by aiding recognition of grain size trends and significant stratal surfaces associated with changes in composition. However, the important wavelengths may differ due to other controls on sandstone composition such as uplift history of the source region, changes in sediment dispersal, and transport mechanisms. • Sample spectral data detect compositional change linked to sandstone grain size. • Compositional change with grain size is detected in airborne spectral data. • Study indicates grain size of siliciclastic successions can be remotely inferred. [ABSTRACT FROM AUTHOR]

An important step in mineral resource estimation process is the grouping of drill hole samples into domains that reflect zones of homogeneous properties for accurate grade estimation and practical exploitation purposes. In practice, this challenging task is performed through a subjective, time-consuming manual interpretation of the mineral deposit. Therefore, various interpretations are possible. The definition of domains can be viewed as a clustering problem consisting of grouping samples into clusters, herein called domains, so that samples belonging to the same cluster are more similar than those in different clusters. Several methods exist for this purpose; however, groups of samples created through traditional clustering tend to show poor spatial contiguity. Alternatively, spatially contiguous clusters can be obtained through geostatistical clustering where the spatial dependency between samples is considered. This paper is devoted to the application of geostatistical clustering to support domaining of an iron ore deposit located in Western Australia. [ABSTRACT FROM AUTHOR]

The use of Shortwave Infrared (SWIR) and Thermal Infrared (TIR) hyperspectral data in mineral exploration has been well documented in many mineralisation types, but is limited in komatiite-hosted nickel sulphide deposits. This project combines hyperspectral, Portable X-ray Fluorescence (pXRF) and whole-rock geochemical data to assess different analytical techniques in the exploration of these deposits. We use the Fisher East nickel sulphide prospects, Western Australia for our case study. The Fisher East prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied. The rocks have undergone intense deformation with primary igneous textures being destroyed, along with strong alteration to talc carbonate assemblages. Combining different analytical tools allowed for differentiation of A and B-zones of original komatiite flows, and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism. By using different lithogeochemical techniques including pXRF, this study shows the Fisher East prospects are hosted within channelised komatiite flows, and have similar characteristics to Kambalda style deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • PRISMA hyperspectral images are promising for rapid mineral detection and mapping. • Feature Extraction Indices are simple but achieve high accuracy in mapping. • Hyperspectral imagery can be used to explore carbonate-hosted base metals deposits. • Hydrothermal dolomites and gossans may be targets for spectral remote sensing. • The method is applicable to other hydrothermal mineralization types in sedimentary basins. Delineating hydrothermal alteration and supergene caps is fundamental for mineral exploration of sulfide ores. The aim of this study is to apply a multi-scale workflow based on hyperspectral remote and proximal sensing data in order to delineate hydrothermal dolomitization and supergene alteration associated with the Mississippi Valley-Type Zn-Pb(-Ag) deposit of Jabali (Western Yemen). The area was investigated through hyperspectral images derived from the new launched Italian Space Agency's PRISMA satellite, which has a higher spectral resolution compared to multispectral sensors and covers the mineral-diagnostic wavelength regions (such as the 2100 nm to 2300 nm range) with a Signal to Noise Ratio (SNR) ≥ 100. Spectral mineral maps were produced through the band ratios method using specific feature extraction indices applied to the hyperspectral satellite data. The results were validated by using Visible Near InfraRed (VNIR) to Short Wave InfraRed (SWIR) reflectance spectra, mineralogical (XRPD) and geochemical (ICP-ES/MS) analyses on rock samples collected in the Jabali area. The dolomites footprint was mapped using a PRISMA Level 2C image, by enhancing the spectral differences between limestones and dolomites in the SWIR-2 region (major features centered at 2340 nm and 2320 nm, respectively). Gossans were detected due to the Fe3+ absorption band in the VNIR region at 900 nm. The Zn-Pb mineralized area, extended for approximately 25 km2, was thus identified by recognizing gossan occurrences in dolomites. The study demonstrates that the PRISMA satellite is effective in identifying Zn-Pb mineralized outcrops in sedimentary basins. [ABSTRACT FROM AUTHOR]

Hyperspectral imaging is a powerful tool for mineral mapping and increasingly used in poorly-accessible areas. It only requires a limited amount of validation sample points, but can fail to discriminate spectrally-similar features. In this manuscript, we show that we improve the identification of interesting targets by including geomorphological data in the spectral mapping scheme. We jointly use geomorphic and spectral features to locate gossanous ironstone ridges as an indicator for possible Pb-Zn-Ag-mineralization and provide an application around Mount Isa and George Fisher/Hilton mine, Queensland, Australia. We combine hyperspectral HyMap data using mixture tuned matched filtering with topographical indices, such as maximum curvature and the topographical position index. As it is often the case with structurally-controlled mineralization, the amount of training sites is limited, and supervised classification methods cannot be implemented. Therefore, we implement expert knowledge in a decision tree to take advantage of the relationship between mineralization, alteration and structure. Optimized rock sampling and spectral measurements provided data for validation. We are able to map sets of gossanous ridges with a minimum of validation points, not only within the Mount Isa mining area itself, but also outside the commonly-accepted host rocks. The ridges are parallel to north-south trending geomorphological features and probably associated with the Paroo fault zone. Similarities between the ridges were confirmed by field observations, spectral measurements and a qualitative rock sample analysis. We identified new mineralized ridges that we could subsequently attribute to a poorly-known and sub-economic deposit known as the Mount Novit Pb-Zn-deposit. [ABSTRACT FROM AUTHOR]

Keywords: Phyllosilicates; glauconite; nontronite; peak shift EN Phyllosilicates glauconite nontronite peak shift 1080 1090 11 06/01/22 20220601 NES 220601 Introduction Raman spectroscopy found widespread application in the rapid and non-destructive characterization of silicate minerals ([26]; [8]; [35]; [34]; [44]; [31]; [1]; [45], 2015; [30]). Concluding remarks In this study, Raman spectroscopy analysis of nontronite and glauconite-nontronite mixed-layer phases from deep-sea hydrothermal fields reveals that these phyllosilicates have diagnostic Raman spectral features that include a series of strong peaks in the low wavenumber region (<700 cm SP -1 sp ) and the hydroxyl domain (3500-3700 cm SP -1 sp ). To fill these knowledge gaps, this study reports a comprehensive Raman spectral characterization of nontronite and glauconite-nontronite mixed-layer phases (i.e., vertical mixing/interstratification of glauconite and nontronite layers) from seafloor hydrothermal fields. Chemistry/structure-dependent Raman spectral features of glauconite and nontronite For the analyzed nontronite and glauconite-nontronite mixed-layer samples, the covariations between Raman spectral properties and octahedral chemistry (Table 2; Figs. [Extracted from the article]

Abstract: Determining the spatial relationships between various geological features and mineralisation is not only important for understanding the ore genesis of mineral deposits, but can also help to guide mineral exploration by providing predictive mineral maps. In this GIS-based study, we quantify the spatial relationships between gold mineralisation and plausible controlling factors in the central part of the St Ives area, Western Australia. We weigh plausible control factors including rock types, lithological boundaries and faults, using gold occurrences in drill-cores, and then apply the weights to the geological data to generate a predictive map for the entire St Ives area. The three major findings of this study are: (1) all major gold deposits are controlled by faults, and small-scale fault systems have a stronger correlation with gold mineralisation than large faults; (2) felsic to intermediate intrusive rocks show strong correlations with gold mineralisation, whereas metamorphic mafic rocks (greenstones) possibly acted as part of the broad regional environment for the mineral province rather than as a factor controlling the exact locations of the deposits; and (3) our predictive mapping indicates that the southeast part of the St Ives goldfield has a high potential for discovering new gold mineralisation. [Copyright &y& Elsevier]

An understanding of the nature of the facies heterogeneity is crucial for successful exploration and development of shale reservoirs. However, shale is a very fine-grained sedimentary rock and it is challenging to understand its heterogeneity through conventional techniques. This paper addresses this challenge for Ordovician Goldwyer Formation (Goldwyer-III shale) through a unique approach by integrating core data with high-resolution image logs (SCMI); petrographic information; Fourier transform infrared (FTIR); and hyperspectral drill core reflectance spectra acquired using a HyLogger3. The petrographic and FTIR data validates the usage of HyLogger3 as a tool to examine high-resolution vertical variations in the shale mineralogy. The results indicate that the Goldwyer-III shale is highly heterogeneous in terms of sedimentary features, organic richness and mineral composition. The studied shale is divided into four facies based on colour, sedimentary features, mineral composition and lithology. The facies include thinly laminated siliceous shale (TLSh), concretionary-banded calcareous shale (CSh), massive black shale (MBSh) and heterolithic shale (HSh). The total organic carbon varies from 0.35 to 4.5 wt% due to variation in facies as a result of fluctuation in oxic-anoxic conditions. The TLSh, MBSh and HSh facies have a higher TOC value (up to 4.5 wt %), T max (up to 450 °C), hydrogen index (up to 250 mgHC/g) and brittleness index (>0.4) comparatively. Whereas, the CSh facies has least TOC, Tmax, hydrogen index and brittleness index. Continuous high-resolution hyperspectral core log data, combined with petrography and conventional core logging, provides a much better understanding of heterogeneity in Goldwyer-III shale. This study offers a new workflow for rapid, continuous and accurate recognition of optimum facies for hydraulic fracturing. This approach can improve economic decisions when developing shale gas reservoirs. Based on TOC and mineralogical derived brittleness index cut-offs values, the high-quality brittle zones are recognised in TLSh and HSh facies deposited in medial (proximal to distal) depositional setting. • The marine shale is highly heterogeneous even at μm scale. • The integration of high resolution data provided a unique workflow for facies classification scheme in shale. • A continuous vertical facies heterogeneity is obtained. • HyLogger3 data with petrography and FTIR is validated for shale. • The influence of depositional setting on shale reservoir potential is discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • PRISMA imagery provides valid support in the delineation of hydrothermal and supergene alteration zones. • Spectral feature parameters aids in identifying and characterising alteration minerals. • Mineral mapping of Porphyry-Cu and IOCG systems assists in mineral exploration at the province- and district-scales. • Hyperspectral satellite interpretation helps in the delineation of new exploration targets. This study provides an overview of the application of hyperspectral imagery acquired by the Italian satellite mission "PRecursore IperSpettrale della Missione Applicativa" (PRISMA), for mapping hydrothermal and supergene mineral alteration zones associated with different Cu deposits in the Chilean Andes. Study areas include the Marimaca Copper Project in the Naguayán district (Antofagasta Province), hosting Late Jurassic – Early Cretaceous iron oxide-copper–gold mineralizations and the Río Blanco-Los Bronces district (Santiago Region) known for its Late Miocene – Early Pliocene copper-molybdenum porphyry deposits. These mineral systems exhibit hydrothermal alteration haloes extending over several kilometers, with upward and outward mineral zonation. To characterize the surface-exposed alteration, the satellite imagery was processed using a multiple feature extraction workflow targeting the relative abundances and compositions of specific supergene and hydrothermal alteration minerals, including Fe-oxides and hydroxides (hematite-goethite), phyllosilicates (micas-kaolinite-chlorite), hydroxyl-bearing sulfates (alunite-natroalunite-jarosite) and epidote. The results reveal a zonation from proximal sulfates (natroalunite to alunite) and Al-rich white mica (ranging from 0.3 km-wide for the area identified to the east of the Marimaca deposit to 1 km-wide in correspondence of the Los Sulfatos deposit, respectively) to distal Al-poor white mica (0.2 to 0.5 km-wide, respectively) and an outer chlorite-epidote zone. In the Marimaca Project area, the structurally-controlled alteration evolves west to east from chlorite-rich to phengitic white mica (Al-poor). A NNE-SSW trending supergene leached cap covers a 6 km-long and up to 2 km-wide area from north to south. Our study documents how spaceborne hyperspectral imaging spectroscopy can support mineral exploration by enabling non-invasive reconnaissance mapping of the outcropping rocks, providing specific targeting information for follow-up field surveys and drilling campaigns. [ABSTRACT FROM AUTHOR]

Abstract: The zinc silicate willemite (Zn2SiO4) is the main carrier of zinc in a number of high-grade, carbonate-hosted nonsulfide deposits located in the southern hemisphere that have been recently reinterpreted to be of hypogene–hydrothermal origin. The timing of willemite mineralization in these deposits is only poorly constrained. In this pilot study, willemite has been evaluated as a potential Rb–Sr geochronometer that can be used to directly date nonsulfide ore deposits. We have analyzed samples of economic-stage willemite from the Berg Aukas and Abenab West deposits, Otavi Mountainland (Namibia), which are hosted by Neoproterozoic, dolomitized and tectonized carbonate rocks. Rb–Sr elemental concentration levels and ranges of 87Rb/86Sr and 87Sr/86Sr ratios in these willemite samples are comparable to those observed for the Zn sulfide sphalerite, which has been already successfully used for direct Rb–Sr dating of carbonate-hosted (MVT) deposits. This reflects similar Rb–Sr partitioning mechanisms into Zn ore minerals that precipitate either as sulfides from reduced or as silicates from oxidized hydrothermal fluids, respectively. The Rb–Sr results on willemite presented here reflect mostly low, but variable 87Rb/86Sr ratios, sufficient to generate radiogenic 87Sr over time. This clearly shows that willemite is suitable as an Rb–Sr geochronometer and should be further evaluated for direct Rb–Sr dating of nonsulfide Zn deposits. Isochron regressions combining samples from Berg Aukas and Abenab West willemites yield Rb–Sr ages in the range of ca. 500 to 560 Ma. These values are geochronologically doubtful at first sight due to high excess data scatter (MSWD=2000 to 3000). Massive, fine-grained willemite samples from Abenab West alone (n =3) give a – still statistically unacceptable (MSWD=60) – isochron regression corresponding to an Rb–Sr age of 574±84 Ma. More reliable ages are obtained from two statistically adequate small-scale Rb–Sr isochron regressions for samples of coarse-grained, well-crystallized Berg Aukas willemite, which yield 499±63 Ma (MSWD=2.6) and 493±2 Ma (MSWD=1.2), respectively. Regardless of the quality of isochron regressions in terms of MSWD, the Rb–Sr ages obtained in this study are fully compatible with other available geochronological data that reflect distinct tectonothermal events in the study area. Therefore, on a regional scale, they appear to be at least geologically reasonable, which has yet to be verified by further studies. Comparable mineralization ages in the range of ca. 490 to 550 Ma are also reflected by the few other known economic, hypogene willemite deposits in the southern hemisphere, for which direct geochronological information is mostly lacking. This may point to a global period of hydrothermal activity in the Cambrian to Lower Ordovician under conditions that favored the formation of hypogene nonsulfide Zn mineralization. [Copyright &y& Elsevier]

A workflow incorporating hyperspectral reflectance data, hull corrections, absorption feature extraction and clustering is presented. The workflow is applied to dense hyperspectral datasets, as collected by hyperspectral drill core logging systems. The extracted absorption features of the reflectance spectra collected from drill cores are shown to form assemblage clusters when plotting the wavelength position of the first, second and third deepest absorption features in two and three dimensions. Using an unsupervised clustering method to establish clusters based on the extracted absorption features yields viewable down hole distributions of similar mineral assemblages. The proposed workflow has the potential for the rapid identification of differing lithologies, alteration and/or weathering overprints. Application of the workflow with no a-priori assumptions about the composition of the potential mineral assemblages provides a means of generating an informative overview of the dataset that is not biased or constrained by preconceptions. The workflow can easily be added to the current workflows of geologists whom are working with dense hyperspectral data to provide an overview of the potential down hole mineral assemblages and aid in the visual logging process or assist in quickly identifying areas for more detailed observation. Furthermore, key mineralogical parameters for resource characterisation, such as the presence of clay minerals can be assessed in a cost and time efficient manner. The proposed workflow is applied to spectra collected from four different drill cores collected in the Gawler Craton located in South Australia and demonstrates the potential outlined above. [ABSTRACT FROM AUTHOR]

• Genetic processes are examined for supergene and hypogene iron ores at Mt Richardson. • Iron ores form by reactivation of hypogene-altered shear zones. • Oxidized supergene fluids removed primary and hypogene quartz from BIF. • Resulting in the formation of high-grade goethite–hematite ores. The Mt Richardson deposit contains high-grade (>57 wt% Fe total) iron ore zones hosted by several banded iron-formations (BIFs) in the c. 3504 Ma Illaara greenstone belt. The BIFs and intervening mafic igneous rocks are exposed along a 700 m-wide, 140 m-high, NNW-trending ridge that demarks the eastern limb of a greenstone belt-scale tight, upright, moderately SSE-plunging syncline. Local expressions of this fold generation include parasitic metre-scale fold hinges, an axial planar fabric, and intersection lineation in BIFs. Margins of tightly folded BIFs are commonly sheared and altered by hypogene magnetite and quartz. Although primary bands are strongly overprinted by disseminated magnetite, the concomitant growth of quartz translates to a negligible increase in the iron content of hypogene-altered BIFs. Reactivation of magnetite–quartz-altered shear zones and interaction with more oxidized fluids led to the replacement of magnetite by martite, precipitation of crystalline hematite, and recrystallization of quartz. Mafic igneous rocks are altered to fine-grained chlorite via replacement of igneous amphibole, biotite, and plagioclase within 30 m of sheared and hypogene-altered BIFs. Hypogene-altered mafic igneous rocks are enriched in Fe 2 O 3total and W, and depleted in MnO, K 2 O, Ca, Na 2 O, and Sr compared to least altered rocks. Subsequent reactivation of shear zones and the circulation of supergene fluids led to dissolution and replacement of primary and hypogene quartz by goethite, and further oxidation of magnetite to martite. Resultant goethite–hematite ore zones are silica-poor, iron-rich, porous, and friable. Alteration indices for supergene-modified, hypogene ore zones in BIFs include hypogene magnetite and hematite in BIFs, chlorite-replacement of primary minerals in mafic igneous rocks, intense supergene goethite–hematite–kaolinite alteration, thinning of primary quartz bands in BIFs, and the presence of broad high-strain zones. Prime exploration targets in the Illaara greenstone belt are areas where these alteration indices coincide with fold-thickened BIFs. Given the friable nature of high-grade iron ore zones, mineralized occurrences are often at least partly hidden and require remote detection methods, followed by drilling, for testing. Mt Richardson differs from most iron deposits in the Yilgarn Craton by the absence of early hypogene carbonate mineral replacement of primary quartz bands in BIFs. Instead, Mt Richardson demonstrates the greater role of supergene fluids that exploit existing structures and permeability via reactivation of hypogene magnetite- and hematite-rich shear zones. In this regard, the Mt Richardson deposit has greater affinity with iron deposits in the Pilbara Craton. [ABSTRACT FROM AUTHOR]

Accurate maps of Earth’s geology, especially its regolith, are required for managing the sustainable exploration and development of mineral resources. This paper shows how airborne imaging hyperspectral data collected over weathered peridotite rocks in vegetated, mountainous terrane in New Caledonia were processed using a combination of methods to generate a regolith-geology map that could be used for more efficiently targeting Ni exploration. The image processing combined two usual methods, which are spectral feature extraction and support vector machine (SVM). This rationale being the spectral features extraction can rapidly reduce data complexity by both targeting only the diagnostic mineral absorptions and masking those pixels complicated by vegetation, cloud and deep shade. SVM is a supervised classification method able to generate an optimal non-linear classifier with these features that generalises well even with limited training data. Key minerals targeted are serpentine, which is considered as an indicator for hydrolysed peridotitic rock, and iron oxy-hydroxides (hematite and goethite), which are considered as diagnostic of laterite development. The final classified regolith map was assessed against interpreted regolith field sites, which yielded approximately 70% similarity for all unit types, as well as against a regolith-geology map interpreted using traditional datasets (not hyperspectral imagery). Importantly, the hyperspectral derived mineral map provided much greater detail enabling a more precise understanding of the regolith-geological architecture where there are exposed soils and rocks. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative iron (oxyhydr-)oxide (Fe-Ox), AlOH-clay and carbonate abundance maps of the Rocklea Dome in Western Australia have been derived from hyperspectral visible-near to shortwave infrared (VNIR–SWIR) airborne data that were compensated for the influence of vegetation cover. The quantitative mineral maps were validated against field data, including ~5500 VNIR–SWIR spectra and ~300 portable X-ray fluorescence measurements. The error on these airborne mineral abundance estimates averages 13.4wt.% Fe for the Fe-Ox abundance, 4.0wt.% Al2O3 for the AlOH-clay abundance and 0.025 for the 2320D parameter used to quantify the carbonate abundance. The unmixed quantitative mineral abundance maps improve geological mapping, including characterisation and exploration for channel iron deposits (CID). In particular, some areas with outcropping CID, which appear subeconomic from the airborne Fe-Ox abundance map without vegetation removal, show as potentially economic CID resources when the influence of vegetation cover is unmixed from the airborne hyperspectral data. These results show that seamless maps of mineral contents can be achieved using data collected from both proximal (drill core and field) and remote (airborne and satellite) hyperspectral sensing systems. [Copyright &y& Elsevier]