1887
Volume 29 Number 1
  • E-ISSN: 1365-2478

Abstract

A

Since its development some thirty years ago, the airborne electromagnetic (AEM) method has been primarily used as a tool for mineral prospecting. However, advanced AEM systems are capable of other tasks, such as geological mapping and groundwater exploration. Excellent correlation between maps of apparent conductivity and geological maps was observed in several regions of Brazil where AEM surveys were performed. The degree of correlation seems to depend on the local climate. In humid and subhumid tropical regions, a weathered layer develops whose thickness and conductivity depend upon bedrock lithology. Therefore certain lithological types can be recognized from their conductivity signature; e.g., granites and Precambrian coarse clastic rocks are resistive, metavolcanic (particularly mafic) and volcanic rocks are conductive, Phanerozoic sediments are generally highly conductive.

Two geophysical surveys are analyzed in the paper. The first was conducted with the time‐domain, towed‐bird AEM system in the Itapicuru greenstone belt in the state of Bahia. The apparent conductivity map correlated better with the local lithology than the magnetic map. Results of the AEM survey were successfully used to improve the regional geological map. A helicopter EM system was used in the second survey, which covered a portion of the Precambrian shield of Rio Grande do Sul. Also in this region ground checks confirmed the usefulness of conductivity surveys in geological mapping.

The technique outlined in the paper holds great promise for countries of humid tropical climate, where few outcrops exist and access is often difficult. The tests performed in Brazil indicate that by executing AEM/aeromagnetic surveys during initial stages of mapping and exploration programs, time and expenditure required for geological field work can be considerably reduced. The resulting geological maps are more accurate and the inventory of mineral occurrences becomes more complete.

Loading

Article metrics loading...

/content/journals/10.1111/j.1365-2478.1981.tb01011.x
2006-04-27
2024-03-28
Loading full text...

Full text loading...

References

  1. Arcone, S.A.1979, Resolution studies in airborne resistivity mapping at VLF, Geophysics44, 937–946.
    [Google Scholar]
  2. Bentes, M., Gonçalves, G.N.D., Daleiro, V. and Costa, A.F.V.1978, Geofisica terrestre e geoquímica sobre anomalias aeromagnéticas na área de Lavras do Sul‐RS, Anais do xxx Congresso, Sociedade Brasileira de Geologia2218–2232.
  3. Beurlen, K.1970, Geologie von Brasilien, Gebrüder Borntraeger, Berlin , 26–101.
    [Google Scholar]
  4. Carvalho, P.F.1932, Reconhecimento geológico no Estado do Rio Grande do Sul, Boletim do Instuto geológico e mineralógico Brasil66, 1–72.
    [Google Scholar]
  5. Cloos, E.1934, Auto‐radio als Hilfsmittel geologischer Kartierung, Zeitschrift fürĠeophysik, 10, 58–66.
    [Google Scholar]
  6. Collett, L.S.1966, Airborne electromagnetic survey over the Winkler aquifer, Manitoba , Geological Survey of Canada Paper66–2, 6–9.
    [Google Scholar]
  7. Collett, L.S.1970, Resistivity mapping by electromagnetic methods, in Morley, L.W. (editor), Mining and groundwater geophysics 1967, Geological Survey of Canada, Ottawa , 615–625.
    [Google Scholar]
  8. Dyck, A.V.1974, Airborne Input surveys, Geological Survey of Canada Paper74–1, 67.
    [Google Scholar]
  9. Fraser, D.C.1978, Resistivity mapping with an airborne multicoil electromagnetic system, Geophysics43, 144–172.
    [Google Scholar]
  10. Fraser, D.C.1979, The multicoil II airborne electromagnetic system, Geophysics44, 1367–1394.
    [Google Scholar]
  11. Hetu, R.J. and Hansen, J.E.1976, Interpretation report of the Santa Luz area, Bahia , Brazil , Geoterrex Ltd., Ottawa, 112.
    [Google Scholar]
  12. Hetu, R.J., Hansen, J.E., Glass, F. and Finney, W.A.1976, Interpretation report of the Caraíba test area and Vale do Curaçá area, Bahia , Brazil , Geoterrex Ltd., Ottawa, 75.
    [Google Scholar]
  13. Hoekstra, P.1978, Electromagnetic methods for mapping shallow permafrost, Geophysics43, 782–787.
    [Google Scholar]
  14. Jackson, V.N., Ramos, V.A., Terry, S.A. and Zuzek, A.B.1973, Projeto aero‐geofisico Camaquã, Estado do Rio Grande do Sul, Texas Instruments, Rio de Janeiro, 125.
    [Google Scholar]
  15. Kishida, A. and Riccio, L.1980, Chemostratigraphy of lava sequencies from the Rio Itapicuru greenstone belt, Bahia, Precambrian Research11, 161–178.
    [Google Scholar]
  16. Lima, O.A.L.1979, Estudo de utilização de reservatórios subterrãneos naturais para armazenamento de água numa área experimental na região semi‐árida do Nordeste Brasileiro, unpublished Ph.D. thesis, Federal University of Bahia, 145.
  17. Makowiecki, L.Z., King, A.S. and Cratchley, C.R.1965, A comparison of three airborne electromagnetic methods of mineral prospecting—Results of test surveys in East Africa, Geological Survey of Canada Paper65–6.
    [Google Scholar]
  18. McNeill, J.D.1977, Interpretation aids—EM‐33 helicopter electromagnetic system, Technical note TN‐4, Geonics Ltd., Mississauga , 13.
    [Google Scholar]
  19. McNeill, J.D.1979, Electrical conductivity of soils and rocks, Technical note TN‐5, Geonics Ltd., Mississauga , 61.
    [Google Scholar]
  20. Moraes, L.C. and Silva, J.F.1978, O distrito cuprífero do Rio Curaçá no contexto geológico regional e possíveis relações de mineralizações de cobre com referencias estratigráficas, Anais do xxx Congresso Sociedade Brasileira de Geologia1533–1544.
  21. Neves, A.S.1977, Levantamento HEM no Rio Grande de Sul—Relatório final, Consórcio LASA-Prospec-Geofoto, Rio de Janeiro, 213.
    [Google Scholar]
  22. Neves, A.S. and Fagundes, P.1978, Prospecção aeroelectromagnética pelo sistema HEM, Mineração e Metalurgia61–396, 4–11.
    [Google Scholar]
  23. Palacky, G.J.1975, Interpretation of Input AEM measurements in areas of conductive overburden, Geophysics40, 490–502.
    [Google Scholar]
  24. Palacky, G.J.1976, Use of decay patterns for the classification of anomalies in time‐domain AEM measurements, Geophysics41, 1031–1041.
    [Google Scholar]
  25. Palacky, G.J.1978, Selection of a suitable model for quantitive interpretation of towed‐bird AEM measurements, Geophysics43, 576–587.
    [Google Scholar]
  26. Palacky, G.J. and Dias, A.C.1978, ProspecçαTo de sulfetos maciços no núcleo pré‐Cambriano de Caçapava do Sul (RS), Anais do xxx Congresso Sociedade Brasileira de Geologia2451–2463.
  27. Palacky, G.J. and Jagodits, F.L.1975, Computer data processing and quantitative interpretation of airborne resistivity surveys, Geophysics40, 818–830.
    [Google Scholar]
  28. Palacky, G.J. and Kadekaru, K.1979, Effect of tropical weathering on electrical and electromagnetic measurements, Geophysics44, 69–88.
    [Google Scholar]
  29. Palacky, G.J. and Sena, F.O.1979, Conductor identification in tropical terrains—Case histories from the Itapicuru greenstone belt, Bahia , Brazil , Geophysics 44, no. 12.
    [Google Scholar]
  30. Palacky, G.J. and West, G.F.1973, Quantitative interpretation of Input AEM measurements, Geophysics38, 1145–1158.
    [Google Scholar]
  31. Paterson, N.R.1970, Exploration for massive sulphides in the Canadian shield, in Morley, L.W. (editor), Mining and groundwater geophysics/1967, Geological Survey of Canada, Ottawa , 275–289.
    [Google Scholar]
  32. Peltoniemi, M.1977, Conductive bedrock and overburden effects on airborne electromagnetic methods used by the Geological Survey of Finland, in Jones, M.J. (editor), Prospecting in areas of glaciated terrain 1977, The Institution of Mining and Metallurgy, London , 89–103.
    [Google Scholar]
  33. Pemberton, R.H.1962, Airborne electromagnetics in review, Geophysics27, 691–713.
    [Google Scholar]
  34. Reischl, J.L.1978, Mineralizações cupriferas associades a vulcânicas da mina Seival (RS), Anais XXX Congr. Brasil . Geol., 1568–1582.
    [Google Scholar]
  35. Ribeiro, M., Bocchi, P.R., Figuereido Filho, P.M. and Tessari, R.I.1966, Geologia de quadricula de Caçapava do Sul, Rio Grande do Sul, Boletim DNPM, Brasil 127, 232.
    [Google Scholar]
  36. Ribeiro, M. and Lichtenberg, E.1978, Síntese da geologia do escudo do Rio Grande do Sul, Anais do xxx Congresso Sociedade Brasileira de Geologia2312–2322.
  37. Seigel, H.O. and Pitcher, D.H.1978, Mapping earth conductivities using a multifrequency airborne electromagnetic system, Geophysics43, 563–575.
    [Google Scholar]
  38. Sinha, A.K.1973, Comparison of airborne EM coil systems placed over a multilayer conducting earth, Geophysics38, 894–919.
    [Google Scholar]
  39. Siqueira, L.P.1978, A evolução geológia do Précambriano no Estado da Bahia e as mineralizações, Anais XXX Congr. Brasil . Geol. 2478–2492.
    [Google Scholar]
  40. Teixeira, G., Gonzales, A.P., Gonzales, M.A. and Licht, O.A.B.1978, Contribuiçõo ao estudo de mineralizações cupríferas disseminadas no distrito minas do Camaquã, Anais do xxx Congresso Sociedade Brasileira de Geologia1644–1654.
  41. Zietz, I., Eaton, G.P., Frischknecht, F.C., Kane, M.F. and Moss, C.K.1976, A western view of mining geophysics in the USSR, Geophysics41, 310–323.
    [Google Scholar]
http://instance.metastore.ingenta.com/content/journals/10.1111/j.1365-2478.1981.tb01011.x
Loading
  • Article Type: Research Article

Most Cited This Month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error