Poisson magnetization-to-density-ratio and magnetization inclination properties of banded iron formations of the Carajás mineral province from processing airborne gravity and magnetic data

According to the Poisson theorem, gravity and magnetic fields arising from geologic bodies that share common sources, with a uniform magnetization-to-density ratio (MDR) and a uniform magnetization direction, are related by a linear transformation that allows each field to be calculated from the other. Provided that these conditions on the sources are met, when the gravity and magnetic data are available over an area, the Poisson theorem can be used to infer the MDRs and magnetization directions of sources from their associated gravity and magnetic anomalies. These conditions are partially met in many geologic structures but are expected in iron ore deposits, usually associated with strongly magnetic and highly dense formations. Due to the importance of iron ore as a global commodity, most mineral provinces of the world have been investigated by accurate gravity and magnetic sensors, providing a reliable database, but they have not yet been explored with joint interpretation based on Poisson’s relationships. We have interpreted a gravity-magnetic survey covering the Serra Sul of the Carajás Mineral Province, Brazil, where world-class iron deposits are found. We have adapted a formulation formerly developed to estimate the MDR and the magnetization inclination (MI) from profile data to process gridded data sets. Due to faulting and folding, the same density and magnetic structure may assume different strike directions, requiring corrections to improve MDR and MI estimates. Because the geomagnetic field inclination in the studied area is very low (−6.7°), a procedure for stable computation of the components of the anomalous magnetic field vector is applied. The inferences for Serra Sul MDR suggest minor variations for the entire 30 km long formation containing the mineralized bodies, the strong remanent magnetization showing reverse polarity for banded iron formation segments of the Carajás Serra Sul.

Download Full-text

Study of Residual Basin and Tectonolayering Based on Airborne Gravity and Magnetic Data

Acta Geologica Sinica - English Edition ◽

10.1111/1755-6724.12116 ◽

2013 ◽

Vol 87 (4) ◽

pp. 1137-1153 ◽

Cited By ~ 4

Author(s):

LI Wenyong ◽

ZHOU Jianxin ◽

XIONG Shengqing ◽

LIU Yanxu ◽

XU Jianchun

Keyword(s):

Magnetic Data ◽

Airborne Gravity ◽

Gravity And Magnetic ◽

Gravity And Magnetic Data

Download Full-text

Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data, Brazil

Tectonophysics ◽

10.1016/j.tecto.2013.12.009 ◽

2014 ◽

Vol 614 ◽

pp. 128-145 ◽

Cited By ~ 81

Author(s):

David L. de Castro ◽

Reinhardt A. Fuck ◽

Jeffrey D. Phillips ◽

Roberta M. Vidotti ◽

Francisco H.R. Bezerra ◽

...

Keyword(s):

Crustal Structure ◽

Magnetic Data ◽

Airborne Gravity ◽

Gravity And Magnetic ◽

Gravity And Magnetic Data ◽

Parnaíba Basin

Download Full-text

Automatic determination of the magnetization–density ratio and magnetization inclination from the joint interpretation of 2D gravity and magnetic anomalies

Geophysics ◽

10.1190/1.1778237 ◽

2004 ◽

Vol 69 (4) ◽

pp. 938-948 ◽

Cited By ~ 7

Author(s):

Carlos Alberto Mendonça

Keyword(s):

Vector Fields ◽

Density Ratio ◽

Magnetic Anomalies ◽

Magnetic Data ◽

Data Sets ◽

Magnetization Direction ◽

Gravity And Magnetic ◽

Geophysical Surveys ◽

Magnetization Density ◽

Gravity And Magnetic Data

The Poisson theorem establishes a linear relationship between the gravity and magnetic potentials arising from common dense and magnetized bodies with constant magnetization–density ratio and magnetization direction. For geological formations satisfying such constraints (i.e., the Poisson conditions), this theorem provides suitable relationships between the gravity and magnetic anomalies that are useful in interpreting the related data sets. In such applications, both magnetization–density ratio (MDR) and magnetization direction can be estimated, thus helping the subsurface geological mapping from potential field data acquired on the earth's surface. However, no existing method is fully automatic, which has hampered extensive use in routine applications. Such a drawback follows the adoption of equations that, although obeying the Poisson theorem, relate particular components of the gravity and magnetic fields, thus requiring either a known magnetization direction or the implementation of iterative procedures to determine it. To allow one‐pass estimates for both MDR and magnetization direction (more precisely, its inclination projected on the plane normal to the source strike), this paper presents simple analytical solutions for these parameters by relating suitable gravity and magnetic vector fields that are derived from the gravity and magnetic data sets. Because current geophysical surveys usually provide only a single‐field component, a data processing scheme is developed to determine the required components in evaluating the desired vector fields. This is done by applying suitable linear transformations on the measured components according to well‐established filtering techniques in processing gravity and magnetic data. Except for distortions from noise, the proposed method automatically determines the MDR and the projected magnetization inclination for the underlying rocks everywhere the Poisson conditions are satisfied. Two‐dimensional sources are assumed, but no constraint upon their depth and cross‐section shape is required. Distorted estimates only appear close to the sources where at least one of the Poisson conditions is violated. In this case, the proposed technique furnishes apparent values for the rock properties. The abrupt changes of apparent values over contacts detect edges, thus facilitating the mapping of geological boundaries. The proposed technique is used to interpret two profiles across the Appalachian fold belt from the eastern portion of the State of Georgia, and the results are compared with some of the geological information available for the area.

Download Full-text

Joint and constrained inversion of magnetic and gravity data: A case history from McArthur River area, Canada

Geophysics ◽

10.1190/geo2019-0818.1 ◽

2020 ◽

pp. 1-76

Author(s):

Mehrdad Darijani ◽

Colin G. Farquharson ◽

Peter G. Lelièvre

Keyword(s):

Joint Inversion ◽

Gravity Data ◽

Real Life ◽

Magnetic Data ◽

Airborne Gravity ◽

Uranium Deposits ◽

Athabasca Basin ◽

Compositional Approach ◽

Gravity And Magnetic ◽

Gravity And Magnetic Data

Magnetic and gravity data are used in the early stages of exploration for uranium deposits in the Athabasca Basin of Canada, just as for many other mineral exploration scenarios. Uranium mineralization in the Athabasca Basin is located where faults in the basement intersect the unconformity between the basement and the overlying sandstones. Both the gravity and magnetic data are dominated by signatures from the basement and an overburden of glacial sediments. The gravity and magnetic data are effective at mapping the basement geology. Any subtle gravity signal from the mineralization related to the formation of the uranium deposits is masked by the signal from the variable thickness overburden. 3D joint inversion of gravity and magnetic data, first without and then with constraints, is evaluated as a means of better determining the structure of the three main lithologies (overburden, sandstones, basement) in the Athabasca Basin. A significant amount of physical property information is available for the main rock units (and overburden), which makes the use of the compositional approach to joint inversion appropriate. For the joint inversion, the fuzzy c-mean clustering method is used. Results from representative synthetic examples show that the joint inversions can construct the overburden and basement structures better than the independent inversions of gravity and magnetic data. Furthermore, constrained joint inversion allows delineation of all three major layers in the area. The same inversion strategies were then applied to the real airborne gravity and magnetic data from the McArthur River area in the eastern Athabasca Basin. The results obtained demonstrate the capabilities of joint inversion for real-life situations.

Download Full-text

Using airborne gravity and magnetic data to recognize crustal domains concealed un-derneath the Parnaíba basin

10.1190/sbgf2013-182 ◽

2013 ◽

Cited By ~ 1

Author(s):

David L. de Castro ◽

Francisco H. R. Bezerra ◽

Jeffrey D. Phillips ◽

Reinhardt A. Fuck ◽

Roberta M. Vidotti

Keyword(s):

Magnetic Data ◽

Airborne Gravity ◽

Gravity And Magnetic ◽

Gravity And Magnetic Data ◽

Parnaíba Basin

Download Full-text

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

Geophysics ◽

10.1190/geo2020-0578.1 ◽

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.

Download Full-text

Lithologic characterization using airborne gravity gradient and aeromagnetic data for mineral exploration: A case study in the Quadrilátero Ferrífero, Brazil

Interpretation ◽

10.1190/int-2014-0195.1 ◽

2015 ◽

Vol 3 (2) ◽

pp. SL1-SL13 ◽

Cited By ~ 18

Author(s):

Cericia Martinez ◽

Yaoguo Li

Keyword(s):

Iron Ore ◽

Physical Property ◽

Density Contrast ◽

Iron Formation ◽

Magnetic Data ◽

Airborne Gravity ◽

Gravity Gradient ◽

Contrast Model ◽

Ore Bodies ◽

Quadrilátero Ferrífero

We present a study on utilizing airborne gravity gradient and magnetic data to characterize an iron ore formation in Minas Gerais, Brazil. The target iron ore bodies have a distinctly high density contrast and produce well-defined anomalies in airborne gravity gradiometry data. The high-grade hematite iron ores are associated with low and moderate susceptibility, making magnetic data useful in distinguishing potential ore bodies from the host iron formation. The airborne gravity gradient and magnetic data over part of the Gandarela Syncline iron formation in the Quadrilátero Ferrífero are independently inverted to obtain a 3D susceptibility and density contrast model. These detailed 3D physical property distributions of subsurface features are then used for geologic characterization and interpretation purposes through lithologic associations. We outline two approaches to link the two physical property distributions and identify representative geologic units in the study area. The geologic units are then organized into a 3D lithology model to help characterize subsurface geologic structure and ore distribution. The lithologic models provide an intuitive representation of the geology and can assist in future exploration plans or in assessment of resource distribution and quality. Our study demonstrates that such approaches are feasible on the deposit scale.

Download Full-text