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Iron ore interpretation using gravity-gradient inversions in the Carajás, Brazil

Leonardo Uieda
November 15, 2012

Iron ore interpretation using gravity-gradient inversions in the Carajás, Brazil

Leonardo Uieda

November 15, 2012
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  1. 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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  2. Carajás survey area

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  6. N1
    plateau

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  7. N1
    plateau
    Target: hematite
    hard (3.6 g/cm3)
    soft (3.4 g/cm3)

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  8. N1
    Survey
    System: FTG
    Line spacing: 150 m
    Height: 100 m
    Total survey: ~550 km

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  9. The data

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  10. Gzz
    N1 geology

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  11. Gzz
    N1 geology

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  12. 3D inversion

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  13. 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

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  14. Planting anomalous densities

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  15. Observed data
    Mesh

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  16. Zero
    density contrast

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  17. Seeds
    (user specified)
    Predicted data

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  18. Neighbors

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  19. The best
    New predicted data

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  20. The best
    New predicted data
    φ=
    √∑
    i=1
    N
    (g
    i
    −d
    i
    )2
    min of Γ=φ+μθ
    and
    compactness

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  21. The best
    New predicted data

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  30. Fit

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  31. Smooth inversion

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  32. Mesh

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  33. min φ( p)=φ
    d
    +μ φ
    p

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  34. min φ( p)=φd
    +μφp
    Densities

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  35. min φ( p)=φd
    +μφp
    Densities Data misfit

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  36. min φ( p)=φd
    +μφp
    Densities Data misfit
    Smoothness + depth weights

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  37. min φ( p)=φd
    +μφp
    subject a⩽ p⩽b
    Densities Data misfit
    Smoothness + depth weights

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  38. True model
    Recovered

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  39. Different methods
    • Different approaches
    • Different constraints
    • Common data
    • Common target

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  40. Inversion parameters
    • Gzz component = 9,053 obs
    • Cell size = 75 m
    – Planting = 581,440 cells
    – Smooth = 1,520,960 cells (larger mesh)

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  41. Seeds
    45 seeds

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  42. Results

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  45. Smooth
    Planting

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  46. Smooth
    Planting

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  47. Cross-section

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  48. Smooth

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  49. Smooth
    Hematite

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  50. Smooth
    Hematite
    Jaspilite

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  51. Planting anomalous densities

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  52. Conclusions
    • Joint interpretation
    • Preliminary results
    • Compatible solutions
    • Agree with boreholes
    • Concentrated above 300 m
    • Bellow 200 m could be jaspilite
    – Same density contrast

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  53. Acknowledgements
    Colorado School of Mines, USA
    Observatório Nacional, Brazil
    Vale S.A.

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