Detailed Lithological Mapping Research Articles

Analysis of Devanur and Manamedu Ophiolite Complexes in SGT, India: A detailed examination employing remote sensing techniques and Laboratory Spectral Signature investigations

This study employs advanced satellite imagery from ASTER and Sentinel-2A to conduct detailed lithological mapping of the Devanur and Manamedu ophiolite complexes in the southern Central Shear Zone (CSZ). The primary focus is on the Manamedu Ophiolite Complex (MOC) and the Devanur Ophiolitic Complex (DOC). Image enhancement techniques such as Color composites, Principal Component Analysis (PCA), and Minimum Noise Fraction (MNF) were utilized to differentiate various rock types. RGB band combinations derived from PCA and MNF outputs demonstrated effective discrimination of rock units. Spectral Angle Mapper (SAM) and Support Vector Machine (SVM) classification methods were employed on ASTER and Sentinel-2A images, yielding classified lithologies that closely matched existing maps from the Geological Survey of India (GSI) and other studies, validating the accuracy of the findings. Additionally, Laboratory Spectral Signature Studies were conducted on 10 rock samples using an ASD FieldSpec Pro® spectroradiometer, providing reflectance spectra from 350 nm to 2500 nm. These spectra, particularly the continuum-removed reflectance, revealed diagnostic absorption features that were corroborated by geochemical analyses. A detailed analysis investigated how elemental compositions and key minerals influenced absorption bands. Major oxide geochemical compositions of DOC and MOC samples were identified using XRF methods. The aim of this research is to characterize DOC and MOC through remote sensing and spectral signature analysis. Sentinel-2A data proved more effective in lithological discrimination compared to ASTER, with spectral signatures indicating the presence of iron (Fe) and magnesium (Mg) contents. Notably, SVM classification of Sentinel-2A MNF + DEM data achieved an overall accuracy of more than 90% when compared with field investigations. This study underscores the efficacy of processing VNIR and SWIR bands from ASTER and Sentinel-2A satellite imagery alongside DEM data and ground surveys for mapping mafic-ultramafic rocks in the DOC and MOC regions of the CSZ.

Basement rocks around the eastern sector of Baranis-Aswan Road, Egypt: Remote sensing data analysis and petrology

The basement rocks around Baranis-Aswan Road, South Eastern Desert of Egypt encompasses a variety of the oldest Pan-African rock units including medium-grade hornblende schist, a variety of gneisses and migmatite as well as medium- to low-grade metavolcanics. These were intruded by syn- to late-tectonic tonalite, granodiorite, quartz diorite as well as gabbros. The exposed basement rock units in the area were discriminated with the detailed lithological mapping using the processed data of ASTER, Landsat-8 and Sentinel-2. Spectral signatures of these rocks were achieved by ASD TerraSpec Halo mineral identifier device. Petrography and geochemistry data enabled to put constraints on their petrogenesis. Geochemically, the schist and gneisses imply K-poor mafic igneous precursors that were developed in a primitive juvenile oceanic environment. The migmatite pertains to stromatic type, whereas granitic magma (neosome) was injected in hornblende schist (paleosome) through cleavage planes. The syn-tectonic tonalite to quartz diorite are also low-K, non-mature calc-alkaline rocks and pertain to oceanic plagiogranite. They display a continuous fractionation evolution trend from quartz-diorite to tonalite and granodiorite.

Rare Earth Elements Assessment in the Granitoids of Part of Southwestern Nigeria

The Rare Earth Elements (REE) composition of granitoids in and around Ila-Orangun area Southwestern Nigeria was assessed in order to ascertain their potential for possible exploitation. Detailed lithological mapping of the area was undertaken followed by whole rock geochemical analysis of representative samples of the granitoids using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) technique. Petrographic study of the samples was carried out as well as the interpretation of the geochemical data using diverse geochemical discrimination plots.
 The rock units mapped were biotite granite gneiss, granite gneiss and hornblende biotite granite. Biotite hornblende gneiss, quartzite, talc-chlorite-tremolite-schist, mica schist and pegmatites were the surrounding country rocks.
 The REE concentrations (in ppm) revealed higher concentrations of the light REEs compared to the heavy REEs. The fractionation ratio, (La/Yb)N ranged from 4.35-15.04 (granite gneiss) and 13.78-18.48 (hornblende biotite granite) indicating enrichment in LREEs over the HREEs. The spider plot for the REEs also showed that the granitoids are LREE-enriched and HREE-depleted suggesting fractional crystallisation and a distinct negative Eu anomaly indicating plagioclase fractionation. Enrichment plot also revealed that the REEs in the granitoids are significantly enriched. Comparison with other areas showed that the granitoids of the study area especially the hornblende biotite granite has higher concentrations of REEs and may be a possible pointer of REE mineralisation.

ASTER spectral band ratios for lithological mapping: a case study for measuring geological offset along the Erkenek Segment of the East Anatolian Fault Zone, Turkey

The current work examines the lithological variation along the Erkenek Segment of the East Anatolian Fault (EAF), a major tectonic structure which accommodates the westward extrusion of Anatolia together with the North Anatolian Fault. Mapping the geology at high spatial resolution along this segment with conventional mapping techniques is highly challenging due to the complex tectonic setting and the abundant number of different lithological units of varying spatial extent. Therefore, in the current study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data along the Erkenek Segment have been used different spectral rationing techniques are applied with band the ratios of 1/3–1/9–3/9, 7/3–1/7–3/5 and 9/5–5/3–3/1 being remarkably useful for detailed lithological mapping and hence detecting the geological offsets along this section of the fault. Thus, these ASTER band ratio images can be used for the lithological mapping along the whole EAF and on other regions in the world with similar lithological and geomorphological conditions.

Remote Sensing for Martian Studies: Inferences from Syrtis Major

Remote sensing techniques have proved to be highly efficient in the exploration of Mars. Availability of several sensors operating across the electromagnetic spectrum on-board orbiters, landers and rovers has helped better understand the surface and atmospheric conditions on the Red planet. This article summarises the application potential of the sensors operating in different wavelength regions for Martian surface studies. Mars unlike Earth allows for utilizing remote sensing techniques in the complete thermal infrared region, owing to narrow absorption regions from a singularly dominant CO2 atmosphere which facilitate detailed lithological mapping. This work also reviews various methodologies adopted till date to study the lithology, mineralogy and fluvial geomorphology including inferences from Syrtis Major volcanic construct. It is evident from the studies, Syrtis Major has well developed fluvial channels mostly attributed to lava flows. However, spectroscopic studies reveal the presence of hydroxylated and hydrated minerals which indicate that lava might not be the sole factor resulting in channel generation in the construct. Future space missions with high resolution payloads targeting this volcanic construct are indispensable to study these channels in detail.

Magnetite-bearing zones in metasediments at Broken Hill, Australia: signatures of black smokers?

High-quality aeromagnetic data show linear magnetic zones within generally non-magnetic metasediments of the Broken Hill and Sundown Groups in the medium- to high-grade metamorphic Willyama Supergroup at Broken Hill, Australia. On-ground investigations show that these anomalies are generated by small amounts of magnetite within the metasediments. The magnetite concentrations are controlled by bedding and transgressed by schistosity. At the outcrop scale, the bedding-parallel nature of the magnetite concentrations is illustrated by decimetre-scale mapping with a magnetic susceptibility meter. At a 1:25 000 scale, there are areas where the relationship between magnetic anomalies and bedding is either unclear or apparently transgressive. Resolution of such situations requires an order of magnitude more detail in both the magnetic data and the geological mapping. This was provided by ground magnetometer surveying, magnetic susceptibility meter surveying and detailed lithological and structural mapping. In the areas studied, no evidence was found for genuinely transgressive relationships between magnetite concentrations and bedding. On a microscopic scale, the magnetite grains are independent of the other main Fe-bearing minerals with no replacement of garnet or biotite by magnetite. Thus, the magnetite did not result from influx of an oxidising fluid during or after high-grade metamorphism. Given that the magnetite concentrations are bedding-parallel and that the magnetite grains are not the result of replacement of ferrous iron-bearing minerals, it is concluded that the magnetite (or its ferric iron precursor) was an original component of the metasediments in these zones. The magnetite does not form clusters as expected with detrital magnetite. The magnetite-bearing zones can be either pelitic or psammitic, so it appears there was not a porosity/permeability control. The most likely origin for the magnetite or its precursor is a rain of particles onto the seafloor from an overlying oxidised water column. Such particles may have been derived from distal plumes resulting from spent orebody-forming fluids. The close relationship in places, between banded iron formation and magnetite-bearing metasediment zones supports this suggestion. Magnetite in metasediments close to the base of Sundown Group may have resulted from spent fluids related to formation of the Broken Hill orebody. However, there are magnetite-bearing metasediment zones within the Broken Hill Group and also stratigraphically higher in the Sundown Group that may be related to as yet undiscovered orebodies. The detailed lithological and structural mapping resulted in some new insights into the structural behaviour of Willyama Supergroup metasediments. In the Yanco Glen southeast area, the distribution of lithologies is largely controlled by D2 shears, producing a series of slices that resemble bedding on aerial photographs. In the Monuments area, D2 shears also control the distribution of lithologies, but extensive melting of psammites and flow parallel to S2 is an added feature.

Processing and interpretation of advanced space-borne thermal emission and reflection radiometer (ASTER) data for lithological mapping in ophiolite complex

The Advanced space-borne thermal emission and reflection radiometer (ASTER) remote sensing data has suitable spectral and spatial properties for detailed lithological mapping. ASTER data is highly effective for lithological mapping in arid and semi-arid regions where geologic structures are extensively exposed. This study has applied spectral transform approaches, consisting of principal component analysis (PCA), band ratio (BR) and minimum noise fraction (MNF) for lithological mapping. As a case study, Abdashtophiolite rock complex located in south eastern Iran has been chosen for applying the image processing techniques to ASTER level 1B data. Prior to image processing, the ASTER data were also subjected to image pre-processing. The results show that PCA images identified the ophiolitic rocks consisting ofamphibolites, undifferentiated pridotite, color melange including ophiolitic component, volcanic rocks, radiolarian cherts, and plagic limestone associated with Eocene sedimentary rocks. ASTER BRs (2+4)/3, (5+7)/6, (7+9)/8) were found best in discriminating the ophiolitic rock units. The MNF transformed data detected rock units more recognizable than PCA and BR techniques. Key words: Advanced space-borne thermal emission and reflection radiometer (ASTER), lithological mapping, ophiolite complex.

Integrating airborne multispectral imagery and airborne LiDAR data for enhanced lithological mapping in vegetated terrain

Practical and financial constraints associated with traditional field-based lithological mapping are often responsible for the generation of maps with insufficient detail and inaccurately located contacts. In arid areas with well exposed rocks and soils, high-resolution multi- and hyperspectral imagery is a valuable mapping aid as lithological units can be readily discriminated and mapped by automatically matching image pixel spectra to a set of reference spectra. However, the use of spectral imagery in all but the most barren terrain is problematic because just small amounts of vegetation cover can obscure or mask the spectra of underlying geological substrates. The use of ancillary information may help to improve lithological discrimination, especially where geobotanical relationships are absent or where distinct lithologies exhibit inherent spectral similarity. This study assesses the efficacy of airborne multispectral imagery for detailed lithological mapping in a vegetated section of the Troodos ophiolite (Cyprus), and investigates whether the mapping performance can be enhanced through the integration of LiDAR-derived topographic data. In each case, a number of algorithms involving different combinations of input variables and classification routine were employed to maximise the mapping performance. Despite the potential problems posed by vegetation cover, geobotanical associations aided the generation of a lithological map – with a satisfactory overall accuracy of 65.5% and Kappa of 0.54 – using only spectral information. Moreover, owing to the correlation between topography and lithology in the study area, the integration of LiDAR-derived topographic variables led to significant improvements of up to 22.5% in the overall mapping accuracy compared to spectral-only approaches. The improvements were found to be considerably greater for algorithms involving classification with an artificial neural network (the Kohonen Self-Organizing Map) than the parametric Maximum Likelihood Classifier. The results of this study demonstrate the enhanced capability of data integration for detailed lithological mapping in areas where spectral discrimination is complicated by the presence of vegetation or inherent spectral similarities.

Lithological mapping of the Troodos ophiolite, Cyprus, using airborne LiDAR topographic data

Traditional field-based lithological mapping can be a time-consuming, costly and challenging endeavour when large areas need to be investigated, where terrain is remote and difficult to access and where the geology is highly variable over short distances. Consequently, rock units are often mapped at coarse-scales, resulting in lithological maps that have generalised contacts which in many cases are inaccurately located. Remote sensing data, such as aerial photographs and satellite imagery are commonly incorporated into geological mapping programmes to obtain geological information that is best revealed by overhead perspectives. However, spatial and spectral limitations of the imagery and dense vegetation cover can limit the utility of traditional remote sensing products. The advent of Airborne Light Detection And Ranging (LiDAR) as a remote sensing tool offers the potential to provide a novel solution to these problems because accurate and high-resolution topographic data can be acquired in either forested or non-forested terrain, allowing discrimination of individual rock types that typically have distinct topographic characteristics. This study assesses the efficacy of airborne LiDAR as a tool for detailed lithological mapping in the upper section of the Troodos ophiolite, Cyprus. Morphometric variables (including slope, curvature and surface roughness) were derived from a 4 m digital terrain model in order to quantify the topographic characteristics of four principal lithologies found in the area. An artificial neural network (the Kohonen Self-Organizing Map) was then employed to classify the lithological units based upon these variables. The algorithm presented here was used to generate a detailed lithological map which defines lithological contacts much more accurately than the best existing geological map. In addition, a separate map of classification uncertainty highlights potential follow-up targets for ground-based verification. The results of this study demonstrate the significant potential of airborne LiDAR for lithological discrimination and rapid generation of detailed lithological maps, as a contribution to conventional geological mapping programmes.

3D IP survey for detailed lithological and structural mapping

As part of the exploration program near the Syama mine in Mali, a 3D resistivity and IP survey was designed for detailed lithological mapping of a partially drilled deposit, about 30 km along strike from the main orebody. Tight line spacing and offsets between transmitting and receiving lines ensured 3D coverage. The survey design had to accommodate simultaneous drilling activity on nearby lines. The combination of resistivity and chargeability measurements map distinct basalt, chert, and graphite lithologies. After 3D inversion, constrained by the available drilling information, the data show structures and folds that will influence resource models.

Three-dimensional mapping of the Platreef at the Zwartfontein South mine: implications for the timing of magmatic events in the northern limb of the Bushveld Complex, South Africa

The Platreef is a pyroxenitic unit with Ni–Cu–PGE mineralisation that forms the base of the layered igneous succession in the northern limb of the Bushveld Complex. It rests upon sediments of the Transvaal Supergroup and Archaean granite/gneiss basement, and is overlain by norites and gabbronorites assigned to the Main Zone of the Complex. Detailed lithological mapping of a series of bench faces on bench 222 of the Zwartfontein South pit was undertaken to define a rectangular block. This information, coupled with drill chip data obtained during the drilling of the blast grids in the enclosing area, has allowed us to constrain with a high degree of confidence the three-dimensional nature of the lithological relationships on a local scale, not achieved by any previous study. The inter-connectivity of the mapped faces has allowed the first well constrained, three-dimensional representation of the Platreef–hangingwall contact to be generated. It has revealed finger-like intrusions of hangingwall gabbronorite which cut down into the Platreef along zones of low competency such as NE–SW and N–S trending shear zones. This relationship demonstrates that the emplacement of Main Zone type hangingwall magma occurred after a significant period of time that had allowed both crystallisation and deformation of the Platreef to take place.

Facies Mapping from Three-Dimensional Seismic Data: Potential and Guidelines from a Tertiary Sandstone-Shale Sequence Model, Powderhorn Field, Calhoun County, Texas

We generated a set of three-dimensional (3-D) seismic models of a lower Miocene progradational microtidal shore-zone system at the Powderhorn field, Calhoun County, Texas. These models were based on detailed lithological mapping of 250 m of stratigraphic section over an area of 13 × 9 km. The mapping was guided by detailed facies analysis based on wireline logs from 115 wells. Fourteen sandy depositional units averaging 3-30 m in thickness are encased in 15 shale units. Density-neutron and spontaneous potential (SP) logs in five recently drilled wells were used to calculate effective porosity and shaliness, which correlate well with P-wave velocity and bulk density logs. Those properties were then extended to older wells lacking acoustic, density, and other porosity ogs through regression with SP and resistivity logs to build 3-D properties models, including models of transit time and impedance. The impedance model was mapped from x, y, z to x, y, t, where t is two-way vertical time. The impedance model was converted to primary reflection coefficient series that were then convolved with zero-phase wavelets of different frequencies to produce the seismic models. The results show how the depositional facies at reservoir scale might be illustrated by 3-D seismic data, and how the seismic resolution of depositional facies changes with seismic frequency, stratigraphic position, and facies patterns. The Powderhorn reservoir sequence is interpreted as a barrier bar/lagoon depositional system associated with coastal stream plains, bayhead deltas, and small wave-dominated deltas corresponding to frequent relative changes of sea level. To detect these types of deposits, the seismic frequency should be selected such that the seismic data are tuned to the maximum thickness to establish a linear relationship between seismic amplitude and facies, and to achieve the best signal-to-noise ratio. The facies associated with the environments where main sandstones are surrounded by muddy deposits, such as coastal stream plain, bayhead delta, delta plain, and backbarrier/lagoon transition, are well illustrated in our seismic model. Lack of muddy deposits, for example in a wave-dominated delta, c uld result in obscure facies boundaries and therefore unclear lithofacies patterns. In this study, poorly compacted clean sandstone and pure shale have similar impedances, and consequently produce similar seismic responses. The resulting ambiguity may be reduced by careful analysis of facies relationships if some well data are available, and probably by the amplitude vs. offset (AVO) method. The stratal resolution of seismic imagery depends not only on wavelet frequency, but also on the stratigraphic position of a given reservoir, or the magnitude of geological interference.

New geologic aspects based on comparative analysis of advanced satellite-and field data in the NE Gulf of Aqaba Area

The current investigations have been carried out within the framework of the special research project 108, sponsored by the German Research Society. Besides other sources, a new generation of satellite data was used to support field campaign. Within a variety of image processing algorithms some application oriented scenes are shown up in the present paper. Thereby, a high impact of information is given by the socalled shortwave infrared bands, not detectable by human eye or photographic systems. Using suitable concepts, optimized presentations can be developed by means of advanced image processing techniques for detailed lithological and structural mapping and for well projected field campaigns.

The early Proterozoic Willyama supergroup: Stratigraphic subdivision and interpretation of high to low‐grade metamorphic rocks in the Broken Hill Block, New South Wales

Abstract A coherent stratigraphy has been recognised in the high to low‐grade multiply‐deformed metamorphic rocks of the Broken Hill Block. The sequence is formally subdivided into sixteen formations and four groups, based on regional interpretation of detailed lithological mapping, structure, and younging criteria. This Early Proterozoic sequence is formally termed the Willyama Supergroup. The supergroup can be extended to sequences in the Early‐Middle Proterozoic metamorphic complexes of the Euriowie, Olary and Mount Painter Blocks, and can be broadly compared with Early Proterozoic sequences in the Gawler Craton. In the Broken Hill Block, the lower sequence in the supergroup comprises migmatites (Clevedale Migmatite) overlain by feldspathic metasedimentary composite gneisses (Thorndale Composite Gneiss). The overlying Thackaringa Group is characterised by quartzofeldspathic gneisses and sodic plagioclase‐quartz rocks. A significant change to well‐bedded, dominantly pelitic metasediments occurs within the overlying Broken Hill Group, which comprises a basal metasediment sequence overlain by an interval containing basic gneiss, garnet‐bearing quartzofeldspathic gneiss and ‘lode horizon’ rocks of the Purnamoota Subgroup. The pelitic metasediment facies extends into the overlying Sundown Group, in which basic and quartzofeldspathic gneisses are absent. The upward trend to more mature sedimentation is apparent in the overlying Paragon Group, which comprises carbonaceous pelitic and fine‐grained psammitic metasediments. The Willyama Supergroup is interpreted as a marine sequence of terrigenous and volcanic elastics, with intercalated felsic and basic volcanics, and rare chemical sediments. The supergroup was deposited in a developing rifted zone, relatively proximal to volcanic sources, which progressed from a shallow, unstable environment, to a more stable deepening environment. Stratiform and stratabound Pb‐Zn‐Ag ± W deposits occur in the Broken Hill Group (more specifically the Purnamoota Subgroup). These include the Broken Hill orebodies, which occur in the Hores Gneiss at the top of the sequence. Within the Thackaringa Group, stratiform cobaltiferous pyrite, and Fe‐Cu sulphides associated with quartz‐magnetite, occur in the Himalaya Formation, and minor Broken Hill‐type Pb‐Zn mineralisation occurs in the Cues Formation.