Marco Antonio Braga

3D Inversion of Airborne Gravity Gradiomentry For Iron Ore Exploration In Brazil

We present the 3D inversion results of gravity gradiometry data over iron ore deposits in Minas Gerais, Brazil. The host formation for the iron ore is largely the Caue Itabirite, along with the overlying Gandalera Formation and, to a lesser degree, the underlying Batatal. Consequently, the iron ore bodies have a distinctly high density contrast and produce well defined anomalies in airborne gravity gradiometry data. We have carried out a preliminary study to apply a 3D inversion to a 20-km2 subarea of data from a larger survey to demonstrate the utility of such an algorithm both in delineatng the ore deposit and in estimating the reserves. We focus on three components of the data (Tzz, Txz, and Tyz). The commonly discussed Tzz component is sufficient to produce geologically reasonable and interpretable results, while including the two horizontal components increases the resolution of the recovered density model and improves the ore delineation.

In-depth imaging of an iron orebody from Quadrilatero Ferrífero using 3D gravity gradient inversion

SUMMARY We have interpreted the airborne gravity gradiometry data from Quadrilatero Ferrifero, an iron ore province in southeastern Brazil. Aiming at retrieving the geometry of the iron body, we have used a fast and novel gravity inversion method for estimating a 3D density-contrast distribution defined on a grid of prisms. This inversion approach combines robust data-fitting with an iterative procedure that does not require the solution of a large equation system. By using a systematic search algorithm, the estimated mass grows around prismatic elements called “seeds”. The interpreter specifies the locations and the associated density contrasts of the seeds. Automatically, the inversion method fits the observations and favors compact gravity sources closest to the seeds. To produce a more robust data fitting than least-squares fit, the inversion method minimizes the L1–norm of the residuals. Hence, it allows the presence of large residuals, so that outliers produced by non-targeted bodies can be handled. By using 126 seeds which were assigned density contrasts of 0.5 g.cm -3 and whose locations were based on our knowledge about the QF area, we have retrieved a continuous elongated iron body that fits the observed components of the gravity gradient. Our inversion result agrees reasonably with previous geophysical interpretations. In addition, our result honors the borehole information about the iron body

Exploração de minério de ferro utilizando dados de aerogradiometria gravimétrica 3D-FTG e aeromagnetometria no Quadrilátero Ferrífero, Minas Gerais, Brasil

This research shows a geological interpretation with focus on iron ore exploration using 3D-FTG airborne gravity gradiometry and airborne magnetic data acquired at Bau-Gandarela region, Quadrilatero Ferrifero, Minas Gerais State, Brazil. The main idea was to establish priorities for hematite prospection in the region cited above. Towards this study was possible to optimize the core drilling, delimiting the best areas for iron ore mineralization, saving economical resources.

Lithologic characterization using magnetic and gravity gradient data over an iron ore formation

Magnetic and gravity gradient data over part of the Gandarela Syncline iron formation in the Quadril´ atero Ferr´ ifero have been utilized to obtain a 3D susceptibility and density contrast model using inversion. It is possible to use these detailed 3D physi- cal property distributions of subsurface features for lithologic interpretation purposes. We group the two physical property distributions into geologically representative units. A distribu- tion of these lithologic units can then be organized in a model similar to the susceptibility and density distributions in order to help characterize subsurface structure.

Planejamento e controle de qualidade de dados de gradiometria gravimétrica 3D-FTG

This research job shows a detailed description of different steps of 3D-FTG (Full Tensor Gravity Gradiometry) planning and quality control (QC). The characteristics of 3D-FTG system, quality control during the flight and the result of the QC recorded through SNR (signal-to-noise ratio) analysis and the synthetical models of each gravity tensor component, will be presented. Iron oxide mineralization style is usually controlled by both crustal and local scale structures such as major shear, fault zones and lithological contacts. Air-FTG (Airborne Full Tensor Gravity Gradiometry) is nowadays the only existing airborne full tensor gradiometer technology can be used for both detailed and regional surveys. The system takes real time measurements of gravity gradient field in three orthogonal directions and at same time compensates for bias in the orientation and accelerations of the aircraft.

Correção de terreno para dados de aerogradiometria gravimétrica 3D-FTG no Quadrilátero Ferrífero, Minas Gerais, Brasil

The aim of this research is to show the application of terrain correction to 3D-FTG data at Bau-Gandarela, Quadrilaterio Ferrifero region at Minas Gerais State, Brazil. For this purpose we have used different digital terrain models with distinct resolutions (SRTM versus lidar).

EVALUATION OF GAMMA-GAMMA WELL LOGGING DATA APPLIED TO IRON ORE EXPLORATION – VALE GEOPHYSICAL WELL LOGGING TEST FACILITY

ABSTRACT. The present paper shows the results of density measurement tests determined by probing of gamma-gamma geophysical well logging, performed in two stages: one at VALE Geophysical Well Logging Test Facility (GWTF), and another in boreholes for iron ore exploration... Keywords: geophysical well logging, iron ore exploration, data evaluation. RESUMO. O presente trabalho mostra os resultados dos testes de afericao de valores de densidades determinados por sonda de perfilagem geofisica gama-gama, realizados em duas etapas, uma no Campo de Teste de Perfilagem Geofisica VALE e outra em furos de sondagem para exploracao de minerio de ferro. Palavras-chave: perfilagem geofisica, exploracao mineral de ferrosos, afericao de dados.

Modelagem numérica e validação de dados tensoriais de aerogradiometria gravimétrica 3D-FTG

Iron oxide mineralization style is usually controlled by both crustal and local scale structures such as major shear, fault zones and lithological contacts. Air-FTG (Airborne Full Tensor Gravity Gradiometry) is nowadays the only existing airborne full tensor gradiometer technology can be used for both detailed and regional surveys. The system takes real time measurements of gravity gradient field in three orthogonal directions and at same time compensates for bias in the orientation and accelerations of the aircraft. Each one of these measurements is related to either the density contrast or the geometry of discrete bodies. The aim of this work was to implement a numerical algorithm to compute the five gxx, gxy, gxz, gyy and gyz independent tensor components and use the knowledge acquired with them to help in real data interpretation and Air-FTG validation. To go over this subject, Air-FTG survey was flown over the Quadrilatero Ferrifero region, in Minas Gerais state, Brazil, to delineate and to map structures associated with iron oxide mineralizations. A complete procedure for data processing, together with joint interpretation of the geological models, ground gravity and air gravity gradiometry tensor components, indicates the high precision capability of the Air-FTG system in mapping and detecting iron oxide bodies with high accuracy. Results show that gradiometer depict a more observable advantage for identification of those near surface targets, revealing structures such as lineament, edges, corners and as a consequence, body shapes and their thickness. We have concluded that the best images of the subsurface rocks acquired by the Air-FTG platform can provide more realistic targets information than the conventional ground gravity field instruments.