Airborne Geophysical Data Sets Research Articles

The Usage of GIS Tools on Vintage Aerogeophysical Data for Simple and Fast Processing with a Focus on Fault Interpretation: An Austrian Case Study

The reuse of vintage datasets which were acquired in the 20th century can pose challenges for modern geophysical modeling due to missing detailed preprocessing information, significant uncertainties, or lack of precise tracking, etc. Nevertheless, they are often the only available datasets in a target region. We explore here the potential of such vintage airborne geophysical datasets (magnetics, AEM, radiometrics) to detect the location and dip direction of geological faults, using a non-modeling interpretation approach based on multiple GIS tools. We apply our approach in a geologically well-known region where four different types of faults are mapped. The applicability of the tools used in this study depend on the geological setting of each fault and is evaluated based on the comparison with geological and—where available—with modeling data. In general, the GIS tools, especially used on a combination of datasets, show reliable results concerning the location and strike of faults, and even seem to be able to predict the dip direction of a fault.

A Random Forest approach to predict geology from geophysics in the Pontiac subprovince, Canada

Current “visual” integration approaches to map geology from geophysics are challenging, biased toward user assumptions, and time consuming. Applying a supervised machine learning Random Forest method to airborne geophysical data sets is an alternative solution to quickly generate interpretative maps, which can later be validated through targeted and therefore more efficient field campaigns. The approach is tested in the Malartic–Cadillac area of the Pontiac subprovince, Canada. Available airborne geophysical data sets include magnetic, frequency-domain electromagnetic, and radiometric data. Unlike the western part of the area, many studies have been done in the eastern part where the world-class Canadian Malartic gold deposit is located. The eastern part has abundant field observations and well-documented geology that are used as training data for Random Forest learning. A predicted map is built after preprocessing the data, gridding the area into a mesh of nodes and training using known geological knowledge. The results provide new information about the spatial distribution of lithological units, including diabase dikes, felsic-intermediate igneous rocks, mafic–ultramafic igneous rocks, and sedimentary rocks. Comparison between the predicted map and previous geological maps could suggest locations where future field mapping efforts should focus in the Malartic–Cadillac area.

To: “Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization,” Seogi Kang, Dominique Fournier, and Douglas W. Oldenburg, Interpretation, 5, no. 3, T327–T340, doi: 10.1190/INT-2016-0141.1.

Previous No AccessInterpretationVolume 5, Issue 4To: “Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization,” Seogi Kang, Dominique Fournier, and Douglas W. Oldenburg, Interpretation, 5, no. 3, T327–T340, doi: 10.1190/INT-2016-0141.1.Authors: Seogi KangDominique FournierDouglas W. OldenburgSeogi KangSearch for more papers by this author, Dominique FournierSearch for more papers by this author, and Douglas W. OldenburgSearch for more papers by this authorhttps://doi.org/10.1190/INT-2017-0815-ERRATUM.1 SectionsAboutFull TextPDF PlusePUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail "To: “Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization,” Seogi Kang, Dominique Fournier, and Douglas W. Oldenburg, Interpretation, 5, no. 3, T327–T340, doi: 10.1190/INT-2016-0141.1.." Interpretation, 5(4), p. Y1FiguresReferencesRelatedDetailsCited byInversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 2: ElectromagneticsDominique Fournier, Seogi Kang, Michael S. McMillan, and Douglas W. Oldenburg7 June 2017 | Interpretation, Vol. 5, No. 3 Volume 5Issue 4Nov 2017Pages: 1N-Y1ISSN (print):2324-8858 ISSN (online):2324-8866 Publisher:Society of Exploration GeophysicistsAmerican Association of Petroleum Geologists HistoryPublished Online: 15 Aug 2017Published in print: 30 Nov 2017 CITATION INFORMATION Seogi Kang, Dominique Fournier, and Douglas W. Oldenburg, (2017), "To: “Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization,” Seogi Kang, Dominique Fournier, and Douglas W. Oldenburg, Interpretation, 5, no. 3, T327–T340, doi: 10.1190/INT-2016-0141.1.," Interpretation 5: Y1-Y1. https://doi.org/10.1190/INT-2017-0815-ERRATUM.1 Plain-Language Summary Metrics Loading ...

Locating hidden channels for placer gold exploration in the Cariboo District, British Columbia, Canada: A case study

During the past 150years, most of the modern day creeks were the target of miners roaming the Cariboo Mountains, British Columbia, in the search for placer gold. In these days, the probability to locate new placer gold occurrence in recent river beds is therefore substantially reduced. New, promising exploration targets appear to be channels mostly buried under alluvial cover sediments. It is airborne geophysical methods that can reveal hidden channels fast and cost-effectively as these penetrate the sub-surface contactless and reflect physical properties of the sub-surface, such as electric conductivity and magnetic susceptibility or magnetization, respectively.We applied the airborne geophysical exploration approach on four exploration areas in the Cariboo gold district. Helicopter-borne transient electromagnetic (TEM) and magnetic data were flown using the SkyTEM system. To our knowledge, it has been innovatory to apply high resolution, high density airborne geophysics in the search for placer gold deposited in pre-Holocene sedimentary channel fills of the Cariboo Mountains. A particular effort of our studies aimed at the Mary creek claims which straddle the boundary of the Quesnel and Kootenay terranes of the Canadian Cordillera and include the dormant Toop mine situated in the Mary creek area known for many finds of coarse nugget from the pre-glacial buried Toop channel. Our objective was to locate the southbound extension of the channel buried in Pleistocene sediments of the Toop plateau. Careful analysis of the airborne geophysical data sets provided indications from both the TEM and magnetic data sets favouring the existence of a hidden channel beneath the plateau.The evaluation of seven reverse circulation (RC) drill holes sunk into a promising elongated narrow conductor beneath the plateau was not conclusive as not clearly showing the sedimentary pattern of a channel with gravels typically at its bottom. Only electric conductivity-depth sections compiled from the airborne TEM and 2D direct current (DC) multi-electrode resistivity ground survey data enabled the interpretation of the airborne TEM and magnetic responses recorded over the Toop plateau. The sections suggest that the electric conductor is generated by an upwarp of a conductive layer extending at the bottom of the Pleistocene sediments. Another feature separated by ≤100m from the conductor line is reflected by low electric conductivity, but is rarely prominent through its neat magnetic signature. Fine accumulations of black minerals, i.e. magnetite grains, in sediments of the area are frequently met when panning material from the creeks. We therefore interpret this low conductivity, magnetic feature as expression of a gravel lense hosting accumulations of magnetite grains and possibly indicating the southbound extension of the Toop channel beneath the plateau.Careful analysis of the airborne magnetic data set led to the result in that magnetite is not only wide-spread in present day rivers and creeks, but also in buried channels and palaeo precipitation run-off paths. Magnetic data proved to be very helpful in this project with regard of pursuing not only present day, but buried valleys and channels, in particular.Our experience made on the Mary creek claims is summarized in a straightforward exploration concept for hidden, possibly gold-bearing channels in the Cariboo gold district.

Lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton: Interplay of coeval contractional deformation and extensional gravitational collapse

We present new litho-structural and metamorphic maps of the Paleoproterozoic (2.25–2.00Ga) West African Craton in northern Ghana, based on the interpretation of field observations and airborne geophysical datasets. The study reveals contrasting metamorphic domains consisting of high-grade gneisses and low-grade volcano–sedimentary belts, separated by shear zones and assembled during the Paleoproterozoic Eburnean orogeny (2.15–2.07Ga). Supracrustal rocks were buried and metamorphosed at conditions corresponding to the amphibolite–granulite facies transition, during a (D1) deformation event, consistent with N–S horizontal shortening, which generated reverse shear zones. High and low metamorphic grade rocks were brought in contact along extensional shear zones formed during N–S extension (D2). These structures were overprinted by contractional deformation associated with E–W shortening and N to NNE stretching (D3), coeval with amphibolite-facies metamorphism. The late-stage tectonic evolution (D4–D7) is characterised by strain localisation in successive generations of narrow shear zones, and the re-activation of inherited structures in a dominantly transcurrent regime. U–Pb dating of zircon and monazite from magmatic and metamorphic rocks reveals that D1-D3 deformations form a continuous and overlapping time sequence between ca. 2140 and 2110Ma. The changes in deformation style from D1 to D3 are interpreted to reflect a shift from dominant horizontal tectonic forces to an interplay between tectonic and gravitational forces, which allowed for the exhumation of the lower crust in an anatectic migmatite dome. We suggest that doming is accommodated by lateral extensional sliding of the upper crust and amplified by coeval orthogonal shortening. The abrupt rotation of shortening directions points to a change in boundary conditions applied to the orogen. We hypothesise that it is due to the collision of northern Ghana with the Paleoproterozoic province in modern-day south-western Burkina Faso, which shows a contrasting geological history. The results reveal that the Eburnean orogeny in NW Ghana shared some thermo-mechanical similarities with modern orogenic belts. The findings bring new insight in Paleoprotezozoic plate tectonics, at the transition between archaic and modern geodynamics.

Sequential and joint hydrogeophysical inversion using a field-scale groundwater model with ERT and TDEM data

Abstract. Increasingly, ground-based and airborne geophysical data sets are used to inform groundwater models. Recent research focuses on establishing coupling relationships between geophysical and groundwater parameters. To fully exploit such information, this paper presents and compares different hydrogeophysical inversion approaches to inform a field-scale groundwater model with time domain electromagnetic (TDEM) and electrical resistivity tomography (ERT) data. In a sequential hydrogeophysical inversion (SHI) a groundwater model is calibrated with geophysical data by coupling groundwater model parameters with the inverted geophysical models. We subsequently compare the SHI with a joint hydrogeophysical inversion (JHI). In the JHI, a geophysical model is simultaneously inverted with a groundwater model by coupling the groundwater and geophysical parameters to explicitly account for an established petrophysical relationship and its accuracy. Simulations for a synthetic groundwater model and TDEM data showed improved estimates for groundwater model parameters that were coupled to relatively well-resolved geophysical parameters when employing a high-quality petrophysical relationship. Compared to a SHI these improvements were insignificant and geophysical parameter estimates became slightly worse. When employing a low-quality petrophysical relationship, groundwater model parameters improved less for both the SHI and JHI, where the SHI performed relatively better. When comparing a SHI and JHI for a real-world groundwater model and ERT data, differences in parameter estimates were small. For both cases investigated in this paper, the SHI seems favorable, taking into account parameter error, data fit and the complexity of implementing a JHI in combination with its larger computational burden.

Application of regional aeromagnetic data in targeting detailed fracture zones

In geological terrains of restricted outcrops the airborne geophysical data sets are important both in regional-scale geological mapping and in assessing local geology. This paper presents a method for predictive mapping of the prevalent fracture directions in bedrock using trend analysis of aeromagnetic high-resolution data. The method was tested using aeromagnetic data from the Fennoscandian Shield in southern Finland. The results of aeromagnetic trend analysis were correlated with geological field tests, and an association between the orientation magnetic trend lines and the orientation of joint sets was detected. Incorporated with structural geological analysis, this method has proved to be effective in the study of bedrock fracturing.

Levelling of helicopter-borne frequency-domain electromagnetic data

For about three decades helicopter-borne electromagnetic (HEM) measurements have been used to reveal the resistivity distribution of the upper one hundred metres of the earth's subsurface. HEM systems record secondary fields, which are 3–6 orders of magnitude smaller than the transmitted primary fields. As both the primary fields and the secondary fields are present at the receivers, well-designed bucking coils are often used to reduce the primary fields at the receivers to a minimum. Remaining parts of the primary fields, the zero levels, are generally corrected by subtracting field values recorded at high altitudes (standard zero levelling) or estimated from resistivities of neighbouring lines or from resistivity maps (advanced zero levelling). These zero-levelling techniques enable the correction for long-term, quasi-linear instrumental drift. Short-term variations caused by temperature changes due to altitude variations, however, cannot be completely corrected by this procedure resulting in stripe patterns on thematic maps. Statistical methods and/or 2-D filter techniques called statistical levelling (tie-line levelling) and empirical levelling (microlevelling), respectively, used to correct stripe patterns in airborne geophysical data sets are, in general, not directly applicable to HEM data. Because HEM data levelling faces the problem that the parameter affected by zero-level errors, the secondary field, differs from the parameter generally levelled, the apparent resistivity. Furthermore, the dependency of the secondary field on both the resistivity of the subsurface and the sensor altitude is strongly nonlinear. A reasonable compromise is to microlevel both half-space parameters: apparent resistivity and apparent depth, followed by a recalculation of the secondary field components based on the half-space parameters levelled. Advantages and disadvantages of the diverse levelling techniques are discussed using a HEM data set obtained in a hilly region along the Saale River between the cities of Saalfeld and Jena in central Germany. It turns out from a comparison of apparent resistivity and apparent depth maps derived from levelled HEM data that manually advanced zero levelling of major level errors and automatic microlevelling of remaining minor level errors yield the best results.

Mapping talc mineralisation and associated alteration using airborne and satellite-borne spectrometry: A case study at Mt Fitton, South Australia

The Mount Fitton talc deposit and associated alteration, located in the northern Adelaide Geosyncline, has been observed to have characteristic spectral signatures in the short-wave infrared and thermal infrared wavelength regions. In particular, reflectance and emissivity spectral measurements of field samples collected in the area have been shown to contain spectral absorption features diagnostic of talc, muscovite/white mica, chlorite, and amphibole minerals. Such minerals are products of the hydrothermal alteration associated with the formation of talc mineralisation. Spectral measurements of field samples also identified other minerals related to the host-rock composition, such as quartz, dolomite, calcite, magnesite and mica/illite. The distinct, and often unique, nature of these spectral signatures indicates the potential for mapping alteration and lithological units at Mount Fitton. Several airborne sensors and recently launched satellite-borne systems have acquired data in the Mount Fitton area, and these data have been processed to evaluate their ability to map the outcropping geology. In particular, the Mount Fitton test site has been used to test various remote-sensing systems with different spectral and spatial resolutions, wavelength ranges and viewing platforms, for their ability to provide useful exploration information, including the location and nature of hydrothermal alteration. Although airborne and satellite-borne multi-spectral systems successfully discriminated geological units and mineral groups, identification of talc and other alteration minerals without a priori information required hyperspectral sensors. It was also found that higher signal-to-noise, spectral resolution and access to different wavelength regions improved the mapping of talc and associated alteration. Spectrally derived mineral maps were found to provide useful supplementary information, which complements traditional airborne geophysical datasets, such as radiometrics or magnetics.

Mapping Mineralogical and structural relationships with satellite-borne ASTER and airborne geophysics at Broken Hill

The recent availability of 14 band multi-spectral and 15 metre DEM data from the satellite borne ASTER (Advanced Spaceborne Thermal Emission Reflection Radiometer) instrument has introduced new possibilities for geological mapping and integration with traditional geophysical data sets. Calibrated radiance at the sensor data and atmospheric corrected ASTER products, such as surface reflectance and emissivity imagery, have been made available by NASA/USGS and the Japanese agency, ERSDAC. ASTER radiance data measures five bands at 30 metre resolution, within the short-wave infrared 2.1 to 2.5 mm wavelength region, and also five bands at 90 metre resolution within the 8 to 12 mm thermal infrared region. This compares with only one band as measured by Landsat TM for each of these regions. An investigation into the capabilities of ASTER and strategies for its integration with geophysical data (using ER Mapper) was undertaken at Broken Hill, given its high spatial geological control and extensive airborne geophysical data sets. Mineral (group) maps derived from multi-scene ASTER data, collected over the Broken Hill Block, proved useful for discriminating stratigraphic units, regolith and areas of alteration. In particular ASTER imagery highlighted several sericite-rich as well as quartz-rich colluvial regolith. Variations in ASTER?s derived AlOH mineral spectral signatures correlated with higher potassium radiometric responses and indicated a change in the muscovite chemistry, possibly due to retrograde metamorphic alteration. However structural features associated with retrograde shear zones were identified most clearly using aeromagnetics. Overall ASTER data products provided complementary mineralogical information to the structural interpretation afforded by geophysical data sets.