Integrated geological and geophysical studies for delineation of chromite deposits: A case study from Tangarparha, Orissa, India

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. B173-B185 ◽  
Author(s):  
William K. Mohanty ◽  
Animesh Mandal ◽  
S. P. Sharma ◽  
Saibal Gupta ◽  
Surajit Misra
Keyword(s):  
Bouguer Anomaly ◽  
Geophysical Methods ◽  
Gravity Anomalies ◽  
High Density ◽  
Geological Mapping ◽  
Magnetic Data ◽  
Ultramafic Rocks ◽  
Dc Resistivity ◽  
Positive Anomaly ◽  
Very High

In Orissa, India, chromite deposits occur in a NE-SW trending belt as discontinuous pods associated with tectonically deformed and metamorphosed ultramafic rocks. Geological mapping and detailed geophysical survey (including gravity, magnetic, electrical, and electromagnetic methods) for exploring chromite were conducted in a [Formula: see text] area at Tangarparha, located within the belt. Lithologies include sheared granite, quartzofeldspathic gneiss, and mafic/ultramafic rocks. The calculated Bouguer anomaly map shows a distinct positive anomaly (up to 16 mGal) in the northern part of the area, indicating the existence of a very high density rock in the subsurface. The trend-surface analysis technique was applied to the gravity and magnetic data for regional-residual separation. The 2D and 2.5D forward modelings of the residual gravity anomaly suggest the presence of lithologies with densities higher than mafic/ultramafic rocks in the subsurface. Chromite fragments recovered from pits within the soil cover around the location indicate that the very high density material is likely to be chromite. Correlation of magnetic and gravity anomalies further emphasizes this possibility. The results of very low frequency (VLF) and DC-resistivity surveys reveal that the suspected chromite deposit is about 250–300 m long in a south-north direction, and 300–350 m wide in the east-west direction. The estimated depth of the deposit varies from 35–100 m. VLF and DC-resistivity methods suggest that chromite occurs in the form of a small disseminated body within a mafic/ultramafic rock matrix. The ambiguity of interpretation is reduced by systematic integration of complementary geophysical methods, compared to that from any single geophysical technique.

scholarly journals MODELAGEM DE DADOS AEROMAGNÉTICOS PARA ESTIMAR LARGURA E ESPESSURA DO COMPLEXO MÁFICO/ULTRAMÁFICO DE CAMPO FORMOSO-BA

2003 ◽  
Vol 52 ◽  
Author(s):  
Francisco José Fonseca Ferreira ◽  
Raimundo Almeida Filho ◽  
Francisco Valdyr Da Silva
Keyword(s):  
Geological Mapping ◽  
Magnetic Data ◽  
Ultramafic Rocks ◽  
Metamorphic Rocks ◽  
Simple Geometry ◽  
Ultramafic Complex ◽  
Northern Portion ◽  
Depth Extent ◽  
Best Fit ◽  
Airborne Magnetic

O complexo máfico/ultramáfico Campo Formoso, no estado da Bahia, é constituído por rochas metamórficas de alto grau, derivadas de peridotitos e piroxenitos do Proterozóico Inferior. Em superfície, ele estende-se por cerca de 40 km, com larguras variando entre 100 e 1.100 metros. A despeito de encerrar as mais importantes mineralizações de cromo conhecidas no Brasil, os conhecimentos geológicos sobre o complexo ainda são bastante limitados. O profundo intemperismo e a presença de coberturas aluviais e coluviais dificultam o mapeamento geológico dessas rochas. Estimativas sobre largura e espessura do complexo em subsuperfície são importantes, visto que, por tratar-se de um corpo estratiforme, níveis mineralizados em superfície podem prolongar-se até grandes profundidades. Neste estudo, dados aeromagnéticos são analisados visando a obter informações sobre a extensão do complexo em subsuperfície. Para isso, um método interativo de modelagem de corpos magnéticos tabulares por processo de inversão foi empregado em uma área selecionada, onde ocorrem alguns dos mais importantes depósitos de cromo conhecidos no complexo. A técnica de modelagem empregada permite o cálculo de parâmetros tais como mergulho, largura e espessura de corpos de geometria simples, magnetizados por indução, remanência, ou ambos. O algoritmo empregado usa valores iniciais para cada parâmetro do corpo a ser modelado, os quais podem ser modificados pelo analista, de modo a incorporar dados reais. Esses dados são manipulados interativamente na busca de um "melhor ajuste", de modo que os parâmetros ajustados caiam dentro de limites de tolerância especificados pelo usuário. A qualidade do ajuste é medida pela relação da soma ponderada dos desvios quadráticos entre valores observados e calculados. Tomando-se como base a geologia da área de estudo, selecionou-se o modelo de dique espesso finito tabular 2 (2¾-D) como o mais apropriado para representar o complexo. Os resultados de modelagens em três perfis indicaram corpos magnéticos com larguras variando entre 264 e 374 metros, espessuras entre 432 e 470 metros e mergulhos entre 52o e 68o para SE. MODELING AIRBORNE MAGNETIC DATA TO ESTIMATE WIDTH AND THICKNESS OF THE MAFIC/ULTRAMAFIC COMPLEX OF CAMPO FORMOSO, BAHIA STATE, BRAZIL Abstract The Campo Formoso complex is located in the Bahia State, in the northeastern part of Brazil. The complex comprises high-grade metamorphic rocks derived from peridotite and pyroxenite of Early Proterozoic age. Mafic/ultramafic rocks cover an area approximately 40 km long and 100 to 1100 m wide, with a general NE-SW direction, dipping to the southeast. This complex hosts the most important chromium deposit of Brazil. This deposit occurs in the southern portion of the complex which makes up a lower structural block, better preserved by the erosion than the northern portion. In spite of its economic importance, geological knowledge of the complex is still very limited. The deep weathering of the mafic/ultramafic rocks and the presence of alluvial and colluvial deposits difficult geological mapping. It is a stratiform complex and the mineralized layers may extend down to great depths. Therefore it is important do know the width and thickness of its rocks in subsurface. In this study airborne magnetic data were analyzed to obtain information of the subsurface extent of the Campo Formoso complex. In order to do that an interactive modeling method of tabular magnetic bodies with inversion process was applied in a selected area of the southern portion of the complex. The used model calculates depth, thickness, and dip of a simple geometry body, magnetized by induction, remanence, or both. This procedure helps to find the best possible match between a theoretical anomaly and a given set of magnetic data. The best fit is found when the adjusted parameters fall within a user-specified tolerance of values which minimize the weighted sum of squared deviations between the observed and the theoretical magnetic anomaly. When a set of parameters satisfies the best-fit criterion, confidence ranges are calculated for all parameters. According to geological data, the best model assumed for the ore body was a thick, flat-topped dyke of finite strike length 2 (2¾-D) and a finite variable depth extent. The modeling results of three profiles of the study area indicate magnetized bodies varying width from 264 to 374 m, thickness from 432 to 473m, and dipping from 52o to 68o SE.

scholarly journals High-resolution aeromagnetic survey of the Teide volcano (Canary Islands): a preliminary analysis

1997 ◽  
Vol 40 (2) ◽  
Author(s):  
A. Garcìa ◽  
I. Blanco ◽  
J. M. Torta ◽  
I. Socías
Keyword(s):  
Bouguer Anomaly ◽  
Magnetic Data ◽  
Positive Anomaly ◽  
Aeromagnetic Survey ◽  
The North ◽  
First Approximation ◽  
Uniform Magnetization ◽  
Reduction To The Pole ◽  
Anomaly Map ◽  
Teide Volcano

To contribute to our understanding of the structure of the Teide volcano, a detailed aeromagnetic survey was carried out covering the area of Las Cañadas caldera and the Teide-Pico Viejo complex. Taking into account the rugged relief of the area (altitude ranges from sea level to almost 4000 m), a terrain correction has been applied. As a first approximation, the topography has been characterized by a uniform magnetization of 5 Am-1 (based on field and laboratory rock magnetic data). Several enhancement techniques have been applied to the residual map (original map minus topographic effect), such as reduction to the pole, pseudogravity integration and upward continuation. In the reduced-to-the-pole map the large positive anomaly that appears centered to the north of Pico Viejo is noteworthy and could be caused by a basaltic intrusion responsible for the last eruptions in this area. Also, a small magnetic low appears over Teide peak, which should be related to slightly-magnetized shallow phonolitic materials. The main tectonic direction of Tenerife, SW-NE, is also clearly reflected on the magnetic anomaly map. The comparison between the pseudogravity and the Bouguer anomaly maps indicates a good correlation between magnetic and gravimetric sources.

Gravity Studies of Earthquake-Related Structures Near Massena, New York

1979 ◽  
Vol 50 (1) ◽  
pp. 13-24
Author(s):  
Reinhard K. Frohlich ◽  
Robert L. Albert ◽  
Frank A. Revetta
Keyword(s):  
New York ◽  
Sea Level ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
River Valley ◽  
Density Contrast ◽  
Positive Anomaly ◽  
Eastern United States ◽  
St Lawrence River

Abstract The causes of the seismicity of the St. Lawrence River Valley are not well understood. As is the case for the entire east coast of North America, epicentral zones often occur in regions where no correlation exists between seismicity and mapped geologic structures. Several explanations have been proposed for such a phenomenon: a) earthquakes occur along unmapped surface faults; b) earthquakes occur along subsurface faults showing no surface expression; or c) the earthquakes are not related to existing faults. Conventional analytical techniques, such as upward and downward continuation, were applied to gravity data from the St. Lawrence River Valley in an attempt to delineate possible seismic–related structures. The analysis of the gravity data indicates that the anomalies trend in a north-northeast direction similar to the structural trends of the Precambrian rocks. The major feature of the Simple Bouguer anomaly map is an extensive positive gravity anomaly centered at Massena, New York. Profiles across the Bouguer gravity anomalies and the up-and downward continued gravity anomalies were reproduced with a two–dimensional modeling technique. Among the various non-unique anomaly-producing structures tested we prefer a model suggesting that the positive anomaly near Massena is derived from two bodies with different density contrasts. The first is a wedge (8 km deep by 35 km wide) located 6 km below sea level with a density contrast of +0.11 gm/cm3 and the second is a smaller body (2 km deep by 6 km wide) located 3.3 km below sea level with a density contrast of +0.2 gm/cm3. The large wedge may represent a sequence of interlayered metasediments and metavolcanics related to the Grenville sequence. The smaller body may represent a mafic intrusive. Several authors have suggested that high gradients of gravity (toward positive) produced by mafic intrusives are associated with earthquakes in the eastern United States. The possible existence of a mafic intrusive near Massena, New York, and its proximity to epicentral zones suggest a similar association for earthquakes in the study area.

3D constrained inversion of gravity and magnetic data to image basement and plutonic bodies: A case study from Dood Arale Basin, eastern Somaliland

Geophysics ◽  
2021 ◽  
pp. 1-57
Author(s):  
Mohammed Y. Ali ◽  
Meixia Geng ◽  
James Derek Fairhead ◽  
Ahmed Adan
Keyword(s):  
Gravity Anomalies ◽  
Geothermal Gradient ◽  
High Density ◽  
Density Model ◽  
Magnetic Data ◽  
Airborne Gravity ◽  
Near Surface ◽  
Gravity And Magnetic ◽  
Seismic Reflection Profiles ◽  
Gravity And Magnetic Data

We have developed 3D inversion models derived from airborne gravity and magnetic data, which are constrained by seismic and well data, in eastern Somaliland. The density model reveals a northwest–southeast-trending basin, 125 km long and 25 km wide and called the Dood Arale Basin. The basin comprises two subbasins separated by a basement high and is infilled by up to 2500–3200 m of sediments. Smaller and shallower subbasins are also identified to the west of Lafaweyne and northeast of Dararweyne. The density model shows that the top basement in the platform areas is at approximately 1500–1700 m in depth and shallows to approximately 300 m at the Bur Anod, Hagraajin and Hagrin Ranges and northwest of Eil Afwein. The basement depths in these areas are more uncertain and could be deeper because they occur in areas of high gravity anomalies caused by a combination of near-surface high-density sediments and high-density plutonic bodies within the basement. The susceptibility model indicates that the basement consists of very weakly magnetized metasediments of the Inda Ad Complex intruded by three northeast–southwest-trending magnetic bodies with upper surfaces at depths of approximately 300–3000 m. These magnetic bodies are interpreted as plutonic complexes of similar age and composition to the Lower Cretaceous syenite intrusions outcropping at Gorei in the Shilah Madu Range. Seismic reflection profiles image the sedimentary sequences, but they do not clearly map the top basement or detect any of the plutonic bodies. The plutonic bodies could have controlled the location of the basin’s border faults and contributed to the high geothermal gradient recorded at the Faro Hills-1 well. The Upper Cretaceous Gumburo and Jesomma Formations in the basin could potentially have reached maturation close to and above the plutonic bodies within the center of the basin.

Exploring rift magmatism and evolution through gravity analysis of North America's failed rifts

2021 ◽  
Author(s):  
Reece Elling ◽  
Seth Stein ◽  
Carol Stein ◽  
G. Randy Keller
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
High Density ◽  
Normal Faults ◽  
Positive Anomaly ◽  
The West ◽  
Midcontinent Rift ◽  
Magmatic Underplating ◽  
Continental Rifts ◽  
History Of

<p>Comparative study of North America’s failed continental rifts allows investigation of the effects of extension, magmatism, magmatic underplating and rift inversion in the evolution of rifting. We explore this issue by examining the gravity signatures of the Midcontinent Rift (MCR), Reelfoot Rift (RR), and Southern Oklahoman Aulacogen (SOA). The ~1.1 Ga MCR records aspects of the complex assembly of Rodina, while the structures related to the ~560 Ma RR and SOA formed during the later breakup of Rodinia and subsequent assembly of Pangea. Combining average gravity anomalies along each rift with seismic data, we examine whether these data support the existence of high-density residual melt underplates (“rift pillows”), reflect the possible amounts of inversion, and whether these rifts should be considered analogs of one another at different stages in rift evolution. The MCR and SOA have strong gravity highs along much of their length. Furthermore, the west and east arms of the MCR have different gravity signatures. The west arm of the MCR has a positive gravity anomaly of 80-100 mgals, while the east arm and SOA have positive anomalies of only 40-50 mgals. The RR does not exhibit a high positive anomaly along much of its length. The positive anomalies of both arms of the MCR and SOA reflect 10-20 km thick underplates at the base of the crust. These gravity anomalies also reflect greater amounts of inversion, during which the rift-bounding normal faults are reactivated by later compression, bringing the high-density igneous rocks closer to the surface. By averaging gravity data along the length of each failed rift, we can more easily distinguish between the history of individual rifts and general features of rifting that apply to other failed or active rifts around the world.</p>

scholarly journals Joint Gravity and Seismic Reflection Methods to Characterize the Deep Aquifers in Arid Ain El Beidha Plain (Central Tunisia, North Africa)

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1310
Author(s):  
Hajer Azaiez ◽  
Hakim Gabtni ◽  
Mourad Bédir
Keyword(s):  
Seismic Reflection ◽  
Large Scale ◽  
Seismic Analysis ◽  
Gravity Data ◽  
Geophysical Methods ◽  
Gravity Anomalies ◽  
Integrated Approach ◽  
Central Tunisia ◽  
Deep Aquifers ◽  
Advanced Analysis

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

Tectonic state and oil-gas prospects of Khidirly-Bandovan structure according to the new gravimetric data

2020 ◽  
pp. 11-18
Author(s):  
A.S. Hasanov ◽  
◽  
◽  
Keyword(s):  
Geophysical Methods ◽  
Geological Mapping ◽  
Seismic Exploration ◽  
Huge Amount ◽  
Ray Method ◽  
Common Depth Point ◽  
Geophysical Surveys ◽  
Gravimetric Data ◽  
Exploration Drilling ◽  
Oil Gas

Khidirly-Bandovan structures have been studied through geological mapping, structural exploration drilling, geophysical methods (gravimetric, magnetic, electrical, seismic exploration methods) since the 1930s. Small amount of oil from different wells in the upper part of Productive Series (PS) and huge amount of gas fountain from Middle Absheron sediments have been obtained. As the interest to these areas had not decreased, the geophysical surveys continued during further years. Seismic exploration surveys were executed in Bandovan structure via Common Depth Point (CDP) method in 2004, refracted ray method and gravimetric exploration complex in 2006 and 3D seismic exploration works and gravimetric investigations with “Scintrex CG-5 Autograv” devices in 2016, correspondingly. In the result of analysis of distribution characteristics for local gravimetric anomalies, as well as 3D descriptions of new gravimetric data, up-to-date logs on tectonic state of Khidirly-Bandovan structure have been obtained and as the new oil-gas exploration objects, the west and south-west wings of these structures highlighted.

scholarly journals Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

2017 ◽  
Vol 47 (1) ◽  
pp. 3-19
Author(s):  
João Gabriel Motta ◽  
Norberto Morales ◽  
Walter Malagutti Filho
Keyword(s):  
Bouguer Anomaly ◽  
Shear Zones ◽  
Magnetic Data ◽  
Gravity Modeling ◽  
West Gondwana ◽  
Fold And Thrust Belt ◽  
Fold Belts ◽  
Thrust Sheets ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

Sign in / Sign up

Export Citation Format

Share Document