Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages ... more Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages that extend far beyond the size of the orebody. Understanding the mineral assemblages and spatial extent of these hydrothermal footprints is crucial for successful exploration, but is commonly hindered by the impact of regolith processes on the Earth's surface. Hyperspectral drill core (HyLogger™-3) data were used to characterise alteration mineralogy at the Mt Olympus gold deposit located 35 km southeast of Paraburdoo along the Nanjilgardy Fault within the northern margin of the Ashburton Basin in Western Australia. Mineralogy interpreted from hyperspectral data over the visible to shortwave (400–2500 nm) and thermal (6000–14500 nm) infrared wavelength ranges was validated with X-ray diffraction and geochemical analyses. Spaceborne multispectral (ASTER) and airborne geophysical (airborne electromagnetic, AEM) data were evaluated for mapping mineral footprints at the surface and sub-...
The Earth's surface comprises minerals diagnostic of weathering, deposition and erosion. The ... more The Earth's surface comprises minerals diagnostic of weathering, deposition and erosion. The first continental-scale mineral maps generated from an imaging satellite with spectral bands designed to measure clays, quartz and other minerals were released in 2012 for Australia. Here we show how these satellite mineral maps improve our understanding of weathering, erosional and depositional processes in the context of changing weather, climate and tectonics. The clay composition map shows how kaolinite has developed over tectonically stable continental crust in response to deep weathering during northwardly migrating tropical conditions from 45 to 10 Ma. The same clay composition map, in combination with one sensitive to water content, enables the discrimination of illite from montmorillonite clays that typically develop in large depositional environments over thin (sinking) continental crust such as the Lake Eyre Basin. Cutting across these clay patterns are sandy deserts that deve...
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
The current stratigraphy of volcanic rocks from the Parana Basin is based mainly on whole rock ge... more The current stratigraphy of volcanic rocks from the Parana Basin is based mainly on whole rock geochemical analyses, which allow the subdivision of the basalt flows in high-TiO2 and low-TiO2 rocks. The work aims to find thermal infrared spectral signatures of the volcanic rocks that correlate with their geochemical signatures. For this, eleven samples were analyzed by FTIR to identify the spectral signature of the basalts and dacites. After that, thin sections of every sample were analyzed. The petrographic, geochemical and spectroscopic data show comparable results. Samples with high TiO2 values contain ilmenite and titano-magnetite, whereas the low-TiO2 rocks contain only titano-magnetite as main Ti-bearing phase. Titano-magnetite and Ilmenite show distinct spectral signatures in the thermal infrared. However, spectral signatures of the rock samples are complicated by overlapping spectral signatures of the single mineral components. The more coarse crystalline samples allow a better separation of the single components when compared to the more fine crystalline samples. The preliminary results suggest that there may be scope to develop thermal infrared spectroscopy as a faster method for lithostratigraphic classification of rocks from the Parana Basin and other volcanic suites worldwide.
... 1 Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 600... more ... 1 Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 6004, Australia; 2 Center for Exploration Targeting, School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia; ...
A mineral systems approach was used to interpret precompetitive airborne mineral mapping geoscien... more A mineral systems approach was used to interpret precompetitive airborne mineral mapping geoscience data for iron oxide copper gold (lOCC) exploration in the Starra area, Eastern Succession, Mount Isa Inlier. Selected minerals were chosen to map possible source rocks/fluids as well as intersecting structural/fluid pathways that could have transported mineralising fluids into domains of contrasting rocks/fluids where there was potential for physicochemical gradients to precipitate metals. Ferric and ferrous iron contents and white mica abundance were useful mineral criteria to identify the Mount Dore Granite of the Williams-Naraku Batholith as a potential source of 'oxidised' fluids rich in Fe, K and potentially Cu-Au. The Mount Dore Shear Zone (MDSZ) intersects the western margin of this granite with the highest contents and changes in composition of the white mica are peripheral to this contact within the granite. This together, with the fact that the entire N-S length of t...
ABSTRACT Determining the spatial relationships between various geological features and mineralisa... more 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.
ABSTRACT Gold production in the Pataz district, northern Peru, is derived from mesothermal veins ... more ABSTRACT Gold production in the Pataz district, northern Peru, is derived from mesothermal veins hosted by the Pataz batholith and basement-hosted epithermal and carbonate–base metal veins. At the regional scale, processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer data can be used to delineate district-scale argillic alteration. One such area extends for tens of kilometres NNW of Vijus in the Maranon Valley. At the southern end of this area, basement-hosted quartz–carbonate–sulfide veins in faults support artisanal gold-mining operations. SEM analyses show that the alteration envelopes around these faults are dominated by illitic clays. These artisanal gold workings highlight the economic potential of the largely unexplored parts of the district-scale argillic alteration zone, further north. At the district scale, paleostress modelling maps areas of low minimum stress during Carboniferous ENE–WSW shortening, based on a new 1:25 000 geological map of the Pataz district. The resulting distribution of low minimum stress is used to predict sites of rock fracture under high fluid pressure, and consequent vein formation. These areas of low minimum stress occupy 11% of the modelled area but contain 50% of the known veins in the Pataz district. Some areas of low minimum stress contain no known veins, and where these are poorly explored or poorly exposed, they are proposed as potential targets for gold exploration. In combination with SEM microanalysis, ASD hyperspectral reflectance analysis of drill core samples shows that visible proximal sericitic alteration around batholith-hosted auriferous veins is predominantly phengitic illite. Automated software interpretation of ASD reflectance spectra using The Spectral Assistant shows that sericite in cryptic alteration distal from auriferous veins varies from mainly illite adjacent to the phengitic illite zone, to more distal muscovite. Reactivation of faults and mineralised vein contacts during the largely Cenozoic Andean orogeny produced chlorite alteration that locally overprints proximal phengitic illite alteration. ASD spectrometry identifies relict phengitic illite in some chloritic alteration zones and thus indicates proximity to mineralised veins at the deposit scale. Elevated pathfinder element concentrations within proximal phengitic illite alteration zones around batholith-hosted veins do not extend more than a few metres beyond the visible alteration envelope. The alkali alteration index [(Rb + Cs)/Th]N is elevated above background levels for up to 15 m beyond the visible sericite alteration zone in one of two holes investigated. In the other hole, both [(Rb + Cs)/Th]N and 3K/Al can be used as a lode-scale vector to gold-bearing veins within broad intersections of visible sericite alteration.
... 1988, 2002; Tolman 1998; Mark & Foster 2000; Belousova et al. 2001; Oliver et al.... more ... 1988, 2002; Tolman 1998; Mark & Foster 2000; Belousova et al. 2001; Oliver et al. 2001). ... Distinct geochemical variations between the Williams and Naraku Granite Suites have been described in recent literature (Belousova et al. ...
Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages ... more Hydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages that extend far beyond the size of the orebody. Understanding the mineral assemblages and spatial extent of these hydrothermal footprints is crucial for successful exploration, but is commonly hindered by the impact of regolith processes on the Earth's surface. Hyperspectral drill core (HyLogger™-3) data were used to characterise alteration mineralogy at the Mt Olympus gold deposit located 35 km southeast of Paraburdoo along the Nanjilgardy Fault within the northern margin of the Ashburton Basin in Western Australia. Mineralogy interpreted from hyperspectral data over the visible to shortwave (400–2500 nm) and thermal (6000–14500 nm) infrared wavelength ranges was validated with X-ray diffraction and geochemical analyses. Spaceborne multispectral (ASTER) and airborne geophysical (airborne electromagnetic, AEM) data were evaluated for mapping mineral footprints at the surface and sub-...
The Earth's surface comprises minerals diagnostic of weathering, deposition and erosion. The ... more The Earth's surface comprises minerals diagnostic of weathering, deposition and erosion. The first continental-scale mineral maps generated from an imaging satellite with spectral bands designed to measure clays, quartz and other minerals were released in 2012 for Australia. Here we show how these satellite mineral maps improve our understanding of weathering, erosional and depositional processes in the context of changing weather, climate and tectonics. The clay composition map shows how kaolinite has developed over tectonically stable continental crust in response to deep weathering during northwardly migrating tropical conditions from 45 to 10 Ma. The same clay composition map, in combination with one sensitive to water content, enables the discrimination of illite from montmorillonite clays that typically develop in large depositional environments over thin (sinking) continental crust such as the Lake Eyre Basin. Cutting across these clay patterns are sandy deserts that deve...
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
The current stratigraphy of volcanic rocks from the Parana Basin is based mainly on whole rock ge... more The current stratigraphy of volcanic rocks from the Parana Basin is based mainly on whole rock geochemical analyses, which allow the subdivision of the basalt flows in high-TiO2 and low-TiO2 rocks. The work aims to find thermal infrared spectral signatures of the volcanic rocks that correlate with their geochemical signatures. For this, eleven samples were analyzed by FTIR to identify the spectral signature of the basalts and dacites. After that, thin sections of every sample were analyzed. The petrographic, geochemical and spectroscopic data show comparable results. Samples with high TiO2 values contain ilmenite and titano-magnetite, whereas the low-TiO2 rocks contain only titano-magnetite as main Ti-bearing phase. Titano-magnetite and Ilmenite show distinct spectral signatures in the thermal infrared. However, spectral signatures of the rock samples are complicated by overlapping spectral signatures of the single mineral components. The more coarse crystalline samples allow a better separation of the single components when compared to the more fine crystalline samples. The preliminary results suggest that there may be scope to develop thermal infrared spectroscopy as a faster method for lithostratigraphic classification of rocks from the Parana Basin and other volcanic suites worldwide.
... 1 Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 600... more ... 1 Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 6004, Australia; 2 Center for Exploration Targeting, School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia; ...
A mineral systems approach was used to interpret precompetitive airborne mineral mapping geoscien... more A mineral systems approach was used to interpret precompetitive airborne mineral mapping geoscience data for iron oxide copper gold (lOCC) exploration in the Starra area, Eastern Succession, Mount Isa Inlier. Selected minerals were chosen to map possible source rocks/fluids as well as intersecting structural/fluid pathways that could have transported mineralising fluids into domains of contrasting rocks/fluids where there was potential for physicochemical gradients to precipitate metals. Ferric and ferrous iron contents and white mica abundance were useful mineral criteria to identify the Mount Dore Granite of the Williams-Naraku Batholith as a potential source of 'oxidised' fluids rich in Fe, K and potentially Cu-Au. The Mount Dore Shear Zone (MDSZ) intersects the western margin of this granite with the highest contents and changes in composition of the white mica are peripheral to this contact within the granite. This together, with the fact that the entire N-S length of t...
ABSTRACT Determining the spatial relationships between various geological features and mineralisa... more 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.
ABSTRACT Gold production in the Pataz district, northern Peru, is derived from mesothermal veins ... more ABSTRACT Gold production in the Pataz district, northern Peru, is derived from mesothermal veins hosted by the Pataz batholith and basement-hosted epithermal and carbonate–base metal veins. At the regional scale, processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer data can be used to delineate district-scale argillic alteration. One such area extends for tens of kilometres NNW of Vijus in the Maranon Valley. At the southern end of this area, basement-hosted quartz–carbonate–sulfide veins in faults support artisanal gold-mining operations. SEM analyses show that the alteration envelopes around these faults are dominated by illitic clays. These artisanal gold workings highlight the economic potential of the largely unexplored parts of the district-scale argillic alteration zone, further north. At the district scale, paleostress modelling maps areas of low minimum stress during Carboniferous ENE–WSW shortening, based on a new 1:25 000 geological map of the Pataz district. The resulting distribution of low minimum stress is used to predict sites of rock fracture under high fluid pressure, and consequent vein formation. These areas of low minimum stress occupy 11% of the modelled area but contain 50% of the known veins in the Pataz district. Some areas of low minimum stress contain no known veins, and where these are poorly explored or poorly exposed, they are proposed as potential targets for gold exploration. In combination with SEM microanalysis, ASD hyperspectral reflectance analysis of drill core samples shows that visible proximal sericitic alteration around batholith-hosted auriferous veins is predominantly phengitic illite. Automated software interpretation of ASD reflectance spectra using The Spectral Assistant shows that sericite in cryptic alteration distal from auriferous veins varies from mainly illite adjacent to the phengitic illite zone, to more distal muscovite. Reactivation of faults and mineralised vein contacts during the largely Cenozoic Andean orogeny produced chlorite alteration that locally overprints proximal phengitic illite alteration. ASD spectrometry identifies relict phengitic illite in some chloritic alteration zones and thus indicates proximity to mineralised veins at the deposit scale. Elevated pathfinder element concentrations within proximal phengitic illite alteration zones around batholith-hosted veins do not extend more than a few metres beyond the visible alteration envelope. The alkali alteration index [(Rb + Cs)/Th]N is elevated above background levels for up to 15 m beyond the visible sericite alteration zone in one of two holes investigated. In the other hole, both [(Rb + Cs)/Th]N and 3K/Al can be used as a lode-scale vector to gold-bearing veins within broad intersections of visible sericite alteration.
... 1988, 2002; Tolman 1998; Mark & Foster 2000; Belousova et al. 2001; Oliver et al.... more ... 1988, 2002; Tolman 1998; Mark & Foster 2000; Belousova et al. 2001; Oliver et al. 2001). ... Distinct geochemical variations between the Williams and Naraku Granite Suites have been described in recent literature (Belousova et al. ...
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