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

2015 ◽  
Vol 3 (2) ◽  
pp. SL1-SL13 ◽  
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.

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

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. K1-K11
Author(s):  
Caio Alencar de Matos ◽  
Carlos Alberto Mendonça
Keyword(s):  
Iron Ore ◽  
Density Ratio ◽  
Iron Formation ◽  
Magnetic Data ◽  
Airborne Gravity ◽  
Magnetic Survey ◽  
Carajás Mineral Province ◽  
Uniform Magnetization ◽  
Gravity And Magnetic ◽  
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.

scholarly journals AIRBORNE GRAVITY GRADIOMETRY – DATA PROCESSING AND INTERPRETATION

2013 ◽  
Vol 31 (3) ◽  
pp. 427 ◽  
Author(s):  
Dionisio Uendro Carlos ◽  
Marco Antonio Braga ◽  
Henry F. Galbiatti ◽  
Wanderson Roberto Pereira
Keyword(s):  
Iron Ore ◽  
A Priori ◽  
Synthetic Data ◽  
Real Data ◽  
Geological Mapping ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Gravity Gradiometry ◽  
Quadrilátero Ferrífero ◽  
Airborne Gravity Gradiometry

ABSTRACT. This paper discusses some processing techniques (all codes were implemented with open source software) developed for airborne gravity gradient systems, aiming at outlining geological features by applying mathematical formulations based on the potential field properties and its breakdown into gradiometric tensors. These techniques were applied to both synthetic and real data. These techniques applied to synthetic data allow working in a controlled environment, under- standing the different processing results and establishing a comparative parameter. These methodologies were applied to a survey area of the Quadrilátero Ferrífero to map iron ore targets, resulting in a set of very helpful and important information for geological mapping activities and a priori information for inversion geophysical models.Keywords: processing, airborne gravity gradiometry, iron ore exploration, FTG system, FALCON system. RESUMO. Neste trabalho apresentamos algumas técnicas de processamento (todos os códigos foram implementados em softwares livres) desenvolvidas para aplicação aos dados de aerogradiometria gravimétrica. Os processamentos foram aplicados tanto a dados sintéticos como a dados reais. A aplicação a dados sintéticos permite atuar em um ambiente controlado e entender o padrão resultante de cada processamento. Esses mesmos processamentos foram aplicados em uma área do Quadrilátero Ferrífero para o mapeamento de minério de ferro. Todos os resultados desses processamentos são muito úteis e importantes para o mapeamento geológicoe como informação a priori para modelos de inversão geofísica.Palavras-chave: processamento, dados de aerogradiometria gravimétrica, exploração de minério de ferro, sistema FTG, sistema FALCON.

Robust 3D gravity gradient inversion by planting anomalous densities

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. G55-G66 ◽  
Author(s):  
Leonardo Uieda ◽  
Valéria C. F. Barbosa
Keyword(s):  
Iterative Algorithm ◽  
Iron Ore ◽  
Density Contrast ◽  
Southeastern Brazil ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Inversion Method ◽  
Multiple Sources ◽  
Sensitivity Matrix ◽  
Current Estimate

We have developed a new gravity gradient inversion method for estimating a 3D density-contrast distribution defined on a grid of rectangular prisms. Our method consists of an iterative algorithm that does not require the solution of an equation system. Instead, the solution grows systematically around user-specified prismatic elements, called “seeds,” with given density contrasts. Each seed can be assigned a different density-contrast value, allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals. In real world scenarios, some sources might not be targeted for the interpretation. Thus, we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources. In our iterative algorithm, the estimated sources grow by the accretion of prisms in the periphery of the current estimate. In addition, only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations. Therefore, the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place, greatly reducing the demand for computer memory and processing time. Tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources, even when interfering signals produced by nontargeted sources are present. Inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of Quadrilátero Ferrífero, southeastern Brazil, we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations.

3D inversion of airborne gravity gradiometry data in mineral exploration: A case study in the Quadrilátero Ferrífero, Brazil

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. B1-B11 ◽  
Author(s):  
Cericia Martinez ◽  
Yaoguo Li ◽  
Richard Krahenbuhl ◽  
Marco Antonio Braga
Keyword(s):  
Iron Ore ◽  
Mineral Exploration ◽  
Density Contrast ◽  
Airborne Gravity ◽  
Gravity Gradiometry ◽  
Inversion Algorithm ◽  
3D Inversion ◽  
Ore Bodies ◽  
Airborne Gravity Gradiometry

We present a case study of applying 3D inversion of gravity gradiometry data to iron ore exploration in Minas Gerais, Brazil. The ore bodies have a distinctly high-density contrast and produce well-defined anomalies in airborne gravity gradiometry data. We have carried out a study to apply 3D inversion to a [Formula: see text] subarea of data from a larger survey to demonstrate the utility of such data and associated inversion algorithm in characterizing the deposit. We examine multiple density contrast models obtained by first inverting [Formula: see text]; then [Formula: see text], [Formula: see text], and [Formula: see text] jointly; and finally all five independent components to understand the information content in different data components. The commonly discussed [Formula: see text] component is sufficient to produce geologically reasonable and interpretable results, while including additional components involving horizontal derivatives increases the resolution of the recovered density model and improves the ore delineation. We show that gravity gradiometry data can be used to delineate the iron ore formation within this study area.

scholarly journals UM MODELO PARA A EVOLUÇÃO MICROESTRUTURAL DOS MINÉRIOS DE FERO DO QUADRILÁTEO FERRÍFERO. PARTE I - ESTRUTURAS E RECRISTALIZAÇÃO

1993 ◽  
Author(s):  
Carlos Alberto Rosière ◽  
Farid Chemale Jr. ◽  
Marcelo L.V. Guimarães
Keyword(s):  
Iron Ore ◽  
Banded Iron Formations ◽  
Lower Proterozoic ◽  
Ore Bodies ◽  
Quadrilátero Ferrífero ◽  
Textural Relationship ◽  
Iron Formations ◽  
Ore District ◽  
Proterozoic Age

In the Quadrilátero Ferrífero iron ore district, the Cauê Formation of the Minas Supergroup comprise banded iron formations, called itabirites, of Lower Proterozoic age enclosing iron rich ore bodies. Although many ore bodies are associated with syntectonic enrichment processes, due to the leaching of gangue minerals like quartz and carbonates, others are probably of sedimentary origin and were recrystallized during the tectonometamorphic development of the region.Three generations of magnetite and four of hematite are recognized in these rocks. They display a clear textural relationship in zones of high and low strain, with the development of two main deformational events under variable metamorphic conditions and different tectonic levels.The first part of this paper one describes the recrystallization phenomena and its relation to the main structures, while in the second part the developed textures and its association to the strain are presented.

Particle swarm optimization inversion of magnetic data: Field examples from iron ore deposits in China

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. J43-J59 ◽  
Author(s):  
Shuang Liu ◽  
Miao Liang ◽  
Xiangyun Hu
Keyword(s):  
Particle Swarm Optimization ◽  
Iron Ore ◽  
Particle Swarm ◽  
Physical Property ◽  
Pso Algorithm ◽  
Ore Deposits ◽  
Source Distribution ◽  
Magnetic Data ◽  
Swarm Optimization ◽  
Iron Ore Deposits

Inspired by the social behavior of birds or fish swarms, particle swarm optimization (PSO) is used to solve many engineering optimization problems. The PSO algorithm is mostly applied to the geophysical parametric inversion based on specific models, and it is rarely used to implement the physical property inversion of geophysical data. We have applied the standard PSO algorithm to the 2D inversion of magnetic data to recover the distribution of subsurface magnetization intensity. To manage the over-stochastic problem of a standard PSO inversion, the velocities of particle swarms are smoothed, and the [Formula: see text]-means clustering model constraint to the objective function is implemented to distinguish the multiple magnetic sources in the case of the complicated magnetic anomaly. The PSO inversion of magnetic data is tested using synthetic models. In the field examples of Galinge and Weigang iron ore deposits in China, concealed iron orebodies were detected, and the reconstructed magnetic source distribution yielded good agreement with the orebodies inferred from drillhole information. The uncertainty analysis results demonstrated that the recovered models using the PSO algorithm had lower reliability for the bottom and boundary areas of target sources because of the influence of observation noise and the weak magnetic response of deep-buried sources. The PSO algorithm obtained a sharp physical property distribution and demonstrated strong global optimization ability.

Geophysical expression of a buried niobium and rare earth element deposit: The Elk Creek carbonatite, Nebraska, USA

2014 ◽  
Vol 2 (4) ◽  
pp. SJ23-SJ33 ◽  
Author(s):  
Benjamin J. Drenth
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Primary Source ◽  
Physical Property ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Magnetic Survey ◽  
Lower Paleozoic ◽  
Vertical Gravity Gradient

The lower Paleozoic Elk Creek carbonatite is a 6–8-km-diameter intrusive complex buried under 200 m of sedimentary rocks in southeastern Nebraska. It hosts the largest known niobium deposit in the U.S. and a rare earth element (REE) deposit. The carbonatite is composed of several lithologies, the relations of which are poorly understood. Niobium mineralization is most enriched within a magnetite beforsite (MB) unit, and REE oxides are most concentrated in a barite beforsite unit. The carbonatite intrudes Proterozoic country rocks. Efforts to explore the carbonatite have used geophysical data and drilling. A high-resolution airborne gravity gradient and magnetic survey was flown over the carbonatite in 2012. The carbonatite is associated with a roughly annular vertical gravity gradient high and a subdued central low and a central magnetic high surrounded by magnetic field values lower than those over the country rocks. Geophysical, borehole, and physical property data are combined for an interpretation of these signatures. The carbonatite is denser than the country rocks, explaining the gravity gradient high. Most carbonatite lithologies have weaker magnetic susceptibilities than those of the country rocks, explaining why the carbonatite does not produce a magnetic high at its margin. The primary source of the central magnetic high is interpreted to be mafic rocks that are strongly magnetized and are present in large volumes. MB is very dense (mean density [Formula: see text]) and strongly magnetized (median 0.073 magnetic susceptibility), producing a gravity gradient high and contributing to the aeromagnetic high. Barite beforsite has physical properties similar to most of the carbonatite volume, making it a poor geophysical target. Geophysical anomalies indicate the presence of dense and strongly magnetized rocks at depths below existing boreholes, either a large volume of MB or another unknown lithology.

scholarly journals Chemical fingerprint of iron oxides related to iron enrichment of banded iron formation from the Cauê Formation - Esperança Deposit, Quadrilátero Ferrífero, Brazil: a laser ablation ICP-MS study

2015 ◽  
Vol 45 (2) ◽  
pp. 193-216 ◽  
Author(s):  
Lucilia Aparecida Ramos de Oliveira ◽  
Carlos Alberto Rosière ◽  
Francisco Javier Rios ◽  
Sandra Andrade ◽  
Renato de Moraes
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Iron Oxides ◽  
Iron Ore ◽  
Redox Conditions ◽  
Iron Formation ◽  
High Grade ◽  
Banded Iron Formation ◽  
Iron Enrichment ◽  
Quadrilátero Ferrífero

<p>Chemical signatures of iron oxides from dolomitic itabirite and high-grade iron ore from the Esperança deposit, located in the Quadrilátero Ferrífero, indicate that polycyclic processes involving changing of chemical and redox conditions are responsible for the iron enrichment on Cauê Formation from Minas Supergroup. Variations of Mn, Mg and Sr content in different generations of iron oxides from dolomitic itabirite, high-grade iron ore and syn-mineralization quartz-carbonate-hematite veins denote the close relationship between high-grade iron ore formation and carbonate alteration. This indicates that dolomitic itabirite is the main precursor of the iron ore in that deposit. Long-lasting percolation of hydrothermal fluids and shifts in the redox conditions have contributed to changes in the Y/Ho ratio, light/heavy rare earth elements ratio and Ce anomaly with successive iron oxide generations (martite-granular hematite), as well as lower abundance of trace elements including rare earth elements in the younger specularite generations.</p>

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