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
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
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
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.