Iron ore interpretation using gravity-gradient inversions in the Carajás, Brazil
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Iron ore interpretation using gravity-gradient inversions in the Carajás, Brazil Dionisio Uendro Carlos Leonardo Uieda* Yaoguo Li Valéria Cristina Ferreira Barbosa Marco Antonio Braga Glauco Angeli Guilherme Gravina Peres
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Presentation given on behalf of Dionisio Uendro Carlos at the 2012 SEG Annual Meeting in Las Vegas.
Transcript of Iron ore interpretation using gravity-gradient inversions in the Carajás, Brazil
Iron ore interpretation using gravity-gradient inversions
in the Carajás, Brazil
Dionisio Uendro CarlosLeonardo Uieda*
Yaoguo LiValéria Cristina Ferreira Barbosa
Marco Antonio BragaGlauco Angeli
Guilherme Gravina Peres
Carajás survey area
N1 plateau
N1 plateau
Target: hematite hard (3.6 g/cm3) soft (3.4 g/cm3)
N1
Survey
System: FTGLine spacing: 150 mHeight: 100 mTotal survey: ~550 km
The data
GzzN1 geology
GzzN1 geology
3D inversion
2 methods
Li, Y. (2001), 3-D inversion of gravity gradiometer data, SEG Expanded Abstracts, 20, 1470–1473, doi:10.1190/1.1816383
Uieda, L., and V. C. F. Barbosa (2012), Robust 3D gravity gradient inversion by planting anomalous densities, Geophysics, 77(4), G55–G66, doi:10.1190/geo2011-0388.1
(1) Planting anomalous densities
(2) Smooth inversion
Planting anomalous densities
Observed data
Mesh
Zero density contrast
Seeds (user specified)
Predicted data
Neighbors
The best
New predicted data
The best
New predicted data
φ=√∑i=1
N
(g i−d i)2
min of Γ=φ+μθ
and
compactness
The best
New predicted data
Fit
Smooth inversion
Mesh
min φ( p)=φd+μφ p
min φ( p)=φd+μφ p
Densities
min φ( p)=φd+μφ p
Densities Data misfit
min φ( p)=φd+μφ p
Densities Data misfit
Smoothness + depth weights
min φ( p)=φd+μφ p
subject a⩽ p⩽b
Densities Data misfit
Smoothness + depth weights
True model
Recovered
Different methods
• Different approaches
• Different constraints
• Common data
• Common target
Inversion parameters
• Gzz component = 9,053 obs
• Cell size = 75 m
– Planting = 581,440 cells
– Smooth = 1,520,960 cells (larger mesh)
Seeds
45 seeds
Results
Smooth
Planting
Smooth
Planting
Cross-section
Smooth
Smooth
Hematite
Smooth
HematiteJaspilite
Planting anomalous densities
Conclusions
• Joint interpretation
• Preliminary results
• Compatible solutions
• Agree with boreholes
• Concentrated above 300 m
• Bellow 200 m could be jaspilite
– Same density contrast
Acknowledgements
Colorado School of Mines, USA
Observatório Nacional, Brazil
Vale S.A.
