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Automatic lithological mapping from potential field data using machine learning: a case study from Mundiyawas-Khera Cu deposit, Rajasthan, India

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Singh B. K. , Gangumalla S. R. , Arasada R. C. , Kumar T.

Acta Geophysica

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2024

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tom Vol. 72, no. 2

777--792

EN

Potential field data play a vital role in mineral resource mapping, especially in deriving the lithological information of poorly mapped terrains. The Mundiyawas-Khera area of the Alwar basin in Rajasthan, India, is known for Cu mineralization hosted within the felsic volcanic rocks. However, much of the area is covered with soil and needs detailed lithological mapping. In this study, different machine learning (ML) algorithms have been employed to integrate the digital elevation, drilling wells, gravity, and magnetic data, together with their derivatives, for obtaining accurate lithology information of the area. Initially, five different ML algorithms, random forest (RF), K-nearest neighbor, support vector machine, multi-layer perceptron (MLP), and gradient boosting (GB) were employed using 540 samples from six lithological units to obtain the refined lithologic map of the area. Subsequently, a stacking classifier was built, considering the best-performing ML models in the base learner. Comparison of evaluation matrices (precision, recall, and confusion matrix) of these ML algorithms suggests that RF, GB, and stack model (RF + GB + MLP with RF meta-classifier) provide the highest accuracy score (RF: 74.69%, GB: 74.69%, and stack: 75.31%) and class membership probabilities in predicting the lithology. Adding derivatives and analytic signal information to the input data improves the classification accuracy of ML models by ~ 5-8%. Overall the study results demonstrate that ensemble ML algorithms can aid in creating the first-pass lithology map of areas with limited outcrops, drilling, and geochemical data.

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Identifying the tectonically induced mineralisation zone in the central part of Dharwar-Shimoga greenstone belt, Western Dharwar Craton: an integrated analysis of gravity and magnetic data

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Das N. , Bhattacharya S. K. , Narayan S. , Livingston D.

Acta Geophysica

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2024

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tom Vol. 72, no. 3

1731--1748

EN

The late Archean Western Dharwar Craton supergroup has volcanic and sedimentary rocks deposited during 2900-2600 Ma underlain by the Sargur Group basement of 3.36-3.2 Ga granitic gneiss and older supracrustal rocks. The western part of the craton, known as the western province (Dharwar Foreland), comprises four major schist belts (Western Ghats-Bababudhan-Shimoga-Chitradurga). A regional gravity and magnetic (Total Field) survey was done in the Shimoga region. The geophysical data of the study area reveal the subsurface extension and behaviour of the exposed rocks of the area. The Euler deconvolution was used to define the depth of the anomaly sources. Euler depth solution for the spherical body (structural index 2), window size = 10, and depth tolerance = 5% depicts the depth of the various sources. The Euler depth solutions cluster over the hook-shaped schist rock of the Medur group (at the northern part of the area) reveals that the body's depth varies from 1 to 4 km in the central part, and at the northern flank, it goes up to 7 km. The solution also brought out the depth of the anomalous body near Hithala, within 4 km. The 2D forward depth modelling of the anomalous zone brings out the involvement of the tectonic forces in the generation of this anomalous body. The more precise depth from the model has been estimated between 2 and 3 km. The model clearly shows the relationship between schist rocks and the basement. However, the high-gravity anomaly has been modelled as the manganese bearing horizon, which has come to optimum depth because of folding and faulting in the region, thus providing a favourable zone for manganese deposition.

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Crustal structure and magmatic system of Isla Socorro (Eastern Pacifc Ocean), derived from the interpretation of geological–geophysical data

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Tapia C. , Yutsis V. , Varley N.

Acta Geophysica

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2021

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tom Vol. 69, no. 6

2051--2067

EN

Isla Socorro is an oceanic island located in the Eastern Pacific Ocean, at the junction of the Clarion Fracture Zone and Mathematician Ridge, approximately 600 km west of the Mexican coastline. Very little is known about the submarine portion of the island, but based on the oldest subaerial deposits, it is inferred to be primarily a basaltic shield cone. In this study, the subsurface structure of Isla Socorro was analysed based on an integration of geological and geophysical data. The geophysical data consist of high-resolution airborne magnetic data as well as an integration of terrestrial gravity and high-resolution satellite gravity. The study revealed important information about the composition, structure and origin of the volcanic edifice. The analysis and interpretation of the gravity and magnetic data indicate the existence of extensional systems associated to the principal tectonic structures of the Revillagigedo area. The horizontal gradient and Euler deconvolution of magnetic data reveal the presence of curved features interpreted as caldera structures. A central, vertically extensive body low in both density and magnetic susceptibility was identified through the 2D forward and 3D inverse modelling techniques. This body could represent a high-temperature zone above the Curie point, thus, we propose this body as a remnant magma reservoir and the source of the most recent volcanic activity from subaerial Socorro, and indicates that the possibility of a future large volume eruption from the summit cannot be ruled out.

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O nowych rozwiązaniach tektonicznych w „Atlasie geologicznym Polski”

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Aleksandrowski P. , Mazur S.

Przegląd Geologiczny

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2017

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tom Vol. 65, nr 12

1499--1510

EN

Authorial comprehensive comments and explanations are given to some of the interpretations applied in the tectonic part of the newly published Geological Atlas of Poland (Nawrocki, Becker, 2017) that considerably change the hitherto generally accepted concepts. It should be, however, admitted that most of those "new’" solutions were already proposed in the past by other workers as hypotheses that could not have been tested in the then state of knowledge on Poland’s deep geology and scientific tools at hand. This has now changed with abundant new data obtained with modern seismic techniques and advanced methods of potential field modelling. Using those data, we justify the reasons for, among others, a significant eastward shifting the front of the Variscan Orogen in Poland andfor the accompanying change in position of the division line between the Precambrian and Palaeozoic platforms. We also show the rationale for accepting a far-reaching southwestward extent of the East European Craton’s crystalline basement below the Palaeozoic Platform and for reinterpretation of the Teisseyre-Tornquist Zone’s nature, together with the question of early Palaeozoic terranes in the TESZ and the situation of the Caledonian foredeep at the SW margin of the East-European Craton.