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

84d34651c3931a54310a57484a109821?s=47 Leonardo Uieda
November 15, 2012

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

84d34651c3931a54310a57484a109821?s=128

Leonardo Uieda

November 15, 2012
Tweet

Transcript

  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
  2. Carajás survey area

  3. None
  4. None
  5. None
  6. N1 plateau

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

  8. N1 Survey System: FTG Line spacing: 150 m Height: 100

    m Total survey: ~550 km
  9. The data

  10. Gzz N1 geology

  11. Gzz N1 geology

  12. 3D inversion

  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
  14. Planting anomalous densities

  15. Observed data Mesh

  16. Zero density contrast

  17. Seeds (user specified) Predicted data

  18. Neighbors

  19. The best New predicted data

  20. The best New predicted data φ= √∑ i=1 N (g

    i −d i )2 min of Γ=φ+μθ and compactness
  21. The best New predicted data

  22. None
  23. None
  24. None
  25. None
  26. None
  27. None
  28. None
  29. None
  30. Fit

  31. Smooth inversion

  32. Mesh

  33. min φ( p)=φ d +μ φ p

  34. min φ( p)=φd +μφp Densities

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

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

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

    Smoothness + depth weights
  38. True model Recovered

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

    data • Common target
  40. Inversion parameters • Gzz component = 9,053 obs • Cell

    size = 75 m – Planting = 581,440 cells – Smooth = 1,520,960 cells (larger mesh)
  41. Seeds 45 seeds

  42. Results

  43. None
  44. None
  45. Smooth Planting

  46. Smooth Planting

  47. Cross-section

  48. Smooth

  49. Smooth Hematite

  50. Smooth Hematite Jaspilite

  51. Planting anomalous densities

  52. Conclusions • Joint interpretation • Preliminary results • Compatible solutions

    • Agree with boreholes • Concentrated above 300 m • Bellow 200 m could be jaspilite – Same density contrast
  53. Acknowledgements Colorado School of Mines, USA Observatório Nacional, Brazil Vale

    S.A.