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3D inversion of SPECTREM and ZTEM airborne electromagnetic data from the Pebble Cu–Au–Mo porphyry deposit, Alaska
Pascal
Pare 1
Alexander V.
Gribenko 2 3
Leif H.
Cox 2
Martin
Čuma 2 3
Glenn A.
Wilson 2 7
Michael S.
Zhdanov 2 3
Jean
Legault 4
Jaco
Smit 5
Louis
Polome 6
1
Anglo American Exploration (Canada) Ltd, 800-700 West Pender Street, Vancouver, British Columbia, V6C 1G8, Canada.
2
TechnoImaging LLC, 4001 South, 700 East, Suite 500, Salt Lake City, Utah, 84107, USA.
3
University of Utah, 115 South, 1460 East, Room 383, Salt Lake City, Utah, 84112, USA.
4
Geotech Ltd, 245 Industrial Parkway North, Aurora, Ontario, L4G 4C4, Canada.
5
Anglo Operations Ltd, 45 Main Street, Johannesburg, 2001, Republic of South Africa.
6
Spectrem Air Ltd, PO Box 457, Lanseria, 1748, Republic of South Africa.
7
Corresponding author. Email: glenn@technoimaging.com
Exploration Geophysics
43(2)
104-115 http://dx.doi.org/10.1071/EG11044
Submitted: 9 September 2011 Accepted: 6 March 2012 Published:
13
April
2012
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Abstract
Geological, geochemical, and geophysical surveys have been conducted in the area of the Pebble Cu–Au–Mo porphyry deposit in south-west Alaska since 1985. This case study compares three-dimensional (3D) inversion results from Anglo American’s proprietary SPECTREM 2000 fixed-wing time-domain airborne electromagnetic (AEM) and Geotech’s ZTEM airborne audio-frequency magnetics (AFMAG) systems flown over the Pebble deposit. Within the commonality of their physics, 3D inversions of both SPECTREM and ZTEM recover conductivity models consistent with each other and the known geology. Both 3D inversions recover conductors coincident with alteration associated with both Pebble East and Pebble West. The high grade CuEqn 0.6% ore shell is not consistently following the high conductive trend, suggesting that the SPECTREM and ZTEM responses correspond in part to the sulphide distribution, but not directly with the ore mineralization. As in any exploration project, interpretation of both surveys has yielded an improved understanding of the geology, alteration and mineralization of the Pebble system and this will serve well for on-going exploration activities. There are distinct practical advantages to the use of both SPECTREM and ZTEM, so we draw no recommendation for either system. We can conclude however, that 3D inversion of both AEM and ZTEM surveys is now a practical consideration and that it has added value to exploration at Pebble.
Key words:
3D, AEM, AFMAG, inversion, Pebble, SPECTREM, ZTEM.
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