Advances in time‐domain electromagnetic surveys at Colorado School of Mines

1983 ◽  
Author(s):  
J. I. Pritchard
Keyword(s):  
Time Domain ◽  
Colorado School ◽  
Time Domain Electromagnetic ◽  
Electromagnetic Surveys

Integrated application of heliborne and ground electromagnetic surveys for mapping EM conductor for uranium exploration and its subsurface validation, North Delhi Fold Belt, Rajasthan, India: A case study

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. B13-B24 ◽  
Author(s):  
A. K. Chaturvedi ◽  
Cas Lotter ◽  
Shailesh Tripathi ◽  
A. K. Maurya ◽  
Indrajit Patra ◽  
...  
Keyword(s):  
Time Domain ◽  
Uranium Mineralization ◽  
Model Parameters ◽  
Fold Belt ◽  
The North ◽  
Geophysical Surveys ◽  
Uranium Exploration ◽  
Time Domain Electromagnetic ◽  
Conducting Bodies ◽  
Electromagnetic Surveys

A fracture-controlled uranium deposit was identified in Proterozoic Ajabgarh metasediments of the North Delhi Fold Belt within the Khetri subbasin at Rohil, Sikar district, Rajasthan, India. Uranium mineralization in the area is associated with geologic structures, albitization, and pyroxenization of metasediments and conductors such as metallic sulfides and carbonaceous phyllites/graphitic schists. To locate uranium mineralization akin to Rohil in nearby thick soil covered areas, this association was targeted through heliborne geophysical surveys. High-resolution heliborne magnetic and time domain electromagnetic (TEM) surveys were conducted around Rohil. The survey delineated several targets with favorable geologic structures and conductors such as graphitic schist for further uranium exploration. One favorable target near Chappar village was taken up for follow-up exploration work. The EM conductor mapped from heliborne survey was subsequently validated through ground time-domain electromagnetic surveys and subsurface exploration. Modeling of heliborne and ground-based electromagnetic data revealed the presence of subsurface conducting bodies with comparable model parameters. Drilling established the presence of a subsurface conductor up to a depth of 300 m, which was attributed to the presence of graphite and sulfides (pyrrhotite) along foliation plane of carbon phyllite/graphitic schist/quartz-biotite schist and calc-silicate rock. Further detailed laboratory investigations (petrology/X-ray diffraction) of selected core samples from the conductive zones confirmed the presence of pyrrhotite and graphite responsible for EM signature. This study, carried out by using multiparameter data sets, proved the efficacy of heliborne surveys in locating favorable targets for uranium exploration in Ajabgarh group of rocks.

Megasource time‐domain electromagnetic sounding methods

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 993-1009 ◽  
Author(s):  
George V. Keller ◽  
James I. Pritchard ◽  
Jimmy Joe Jacobson ◽  
Norman Harthill
Keyword(s):  
Time Domain ◽  
Vertical Component ◽  
High Amplitude ◽  
Colorado School ◽  
Electromagnetic Sounding ◽  
The Earth ◽  
Field Versus ◽  
Time Domain Electromagnetic ◽  
Em Field ◽  
Depth Of Investigation

The Colorado School of Mines time‐domain electromagnetic (EM) sounding system makes use of a grounded length of cable powered with high‐amplitude current square waves to generate an EM field for probing the earth. The vertical component of magnetic induction is detected at a sounding site located at a relatively large distance compared to the desired depth of investigation. With a source moment of a million ampere meters or greater, offset distances of several tens of kilometers can be achieved easily, providing depths of investigation of up to 10 km. The recorded induction field versus time curves are routinely interpreted by comparison with computer‐generated theoretical curves for a layered earth. Megasource EM surveys have been carried out at The Geysers in northern California and near Yakima in central Washington, providing apparently meaningful information on the electrical structure in these areas at depths as great as 10 km.

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