Induced-polarization surveys applied to exploration for roll-front uranium deposits

Abstract

This open-file report summarizes the oral presentation given at the 45th Annual Meeting of the Society of Exploration Geophysicists. The data analysis given here is brief because of time limitations imposed at the meeting. A more detailed analysis of the data (both geological and geophysical) will be given in subsequent publications. Our oral presentation was preceded by one given by Jeffrey Daniels and James Scott entitled "Borehole Investigations of South Texas Uranium Deposits." Statements made in their presentation that are pertinent to this report are as follows: (1) a Tertiary sandstone is the host for the South Texas uranium occurrence, (2) the roll-front geometry is similar to those found in Wyoming, and (3) the roll-front does not occur at a visually obvious change from reduced to oxidized environments. A careful comparison of the IP (induced polarization) borehole logs and lithology revealed the following general points: (1) the largest IP response logged in the boreholes occurred at the uranium roll-front, and (2) the IP response can be correlated with percentage pyrite and with variations in the percentage and type of clay present. The IP measurements reported here were made with a time-domain Huntec IP receiver. The transmitted wave-form had a two-second on-and-off period. Four windows were measured during the off-time. The second window, M2, which is given here, has a window duration of 130 milliseconds from 50 to 130 milliseconds. IP coupling is inferred not to be a serious problem in the survey data reported here, because the variations in M measurements are the same as those seen for the2 window of longest delay and length. The data presented herein are part of a broad data set which the U.S. Geological Survey has gathered on surface geophysical methods. Other people who have been involved in the data collection, interpretation, and presentation are John Cady, David Campbell, Ralph Corken, Richard Meyer, Louis O'Connor, Tommas Nash, and James Scott.