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

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

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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

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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

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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.