- Email: [email protected]
High resolution airborne magnetics and gamma-ray spectrometry for reconnaissance geological mapping
216
HIGH RESOLUTION AIRBORNE MAGNETICS AND GAMMA-RAY SPE~ROMETRY FOR RECONNAISSANCE GEOLOGICAL MAPPING
S. BREINER GeoMetrics
International
Corporation,
Palo Alto,
Calif. (U.S.A.)
The combined utilization of large-detector-volume differential gammaray spectrometers, higher resolution magnetometers, and proper analytical techniques represents a new, promising and effective technique for geological mapping over large virgin areas. As a follow-up procedure after photo interpretation, spectrometers and magnetometers are conveniently flown at the same altitude and speeds and in the same aircraft; they require similar treatment of data; and they provide significantly better and less costly information over a large area than either one alone or than would be obtained from corresponding ground measurements. Gamma-ray data provides information related to surface or near-surface rock types and inferred structure whereas magnetics include the effects of sub-surface as well as near-surface structure and lithology. Supported by subsequently acquired geologic control, the geophysical maps and geological interpretation become infinitely more valuable in a geological mapping program and greatly reduce requirements and costs for ground geological mapping. Surveys are presently being flown with differential spectrometer crystal volume in excess of 1,000 cu. inches, ma~etometers of 0.5-0.1 gamma resolution, and digital recording and processing of all data. Interpretation of the ratios of potassium, uranium, and thorium even over widely-spaced survey lines has been demonstrated to be useful for mapping near-surface contacts between acidic and basic or sedimentary rocks; contacts between different sedimentary formations; and contacts of other lithologies with subtle differences in potassium, uranium or thorium or their ratios. Interpretation of the magnetics using depth-to-source as well as plan-view criteria allows geological interpretation of intrusives, buried contacts, configuration of basins, magnetic basement topography, faults and rock-type as related to magnetite content. Digital processing and precision Doppler navigation facilitate the perfo~ance of such surveys and allow for rapid and efficient compilation and interpretation of the data.
HIGH RESOLUTION AIRBORNE MAGNETICS AND GAMMA-RAY SPE~ROMETRY FOR RECONNAISSANCE GEOLOGICAL MAPPING
S. BREINER GeoMetrics
International
Corporation,
Palo Alto,
Calif. (U.S.A.)
The combined utilization of large-detector-volume differential gammaray spectrometers, higher resolution magnetometers, and proper analytical techniques represents a new, promising and effective technique for geological mapping over large virgin areas. As a follow-up procedure after photo interpretation, spectrometers and magnetometers are conveniently flown at the same altitude and speeds and in the same aircraft; they require similar treatment of data; and they provide significantly better and less costly information over a large area than either one alone or than would be obtained from corresponding ground measurements. Gamma-ray data provides information related to surface or near-surface rock types and inferred structure whereas magnetics include the effects of sub-surface as well as near-surface structure and lithology. Supported by subsequently acquired geologic control, the geophysical maps and geological interpretation become infinitely more valuable in a geological mapping program and greatly reduce requirements and costs for ground geological mapping. Surveys are presently being flown with differential spectrometer crystal volume in excess of 1,000 cu. inches, ma~etometers of 0.5-0.1 gamma resolution, and digital recording and processing of all data. Interpretation of the ratios of potassium, uranium, and thorium even over widely-spaced survey lines has been demonstrated to be useful for mapping near-surface contacts between acidic and basic or sedimentary rocks; contacts between different sedimentary formations; and contacts of other lithologies with subtle differences in potassium, uranium or thorium or their ratios. Interpretation of the magnetics using depth-to-source as well as plan-view criteria allows geological interpretation of intrusives, buried contacts, configuration of basins, magnetic basement topography, faults and rock-type as related to magnetite content. Digital processing and precision Doppler navigation facilitate the perfo~ance of such surveys and allow for rapid and efficient compilation and interpretation of the data.