Airborne gamma-ray spectrometer and magnetometer survey: Sioux Falls quadrangle, South Dakota. Volume I. Final report

Abstract

Computer printer maps of the magnetic total intensity and the six radiometric parameters have been prepared in addition to the radiometric anomaly maps for this area. The magnetic total intensity map displays a rather subdued response pattern of broad low amplitude anomalies over much of the area with an average magnetic intensity of approximately 58,900 gammas. The radiometric response over much of the area is relatively low. Equivalent concentrations of uranium, thorium and potassium only rarely exceed 3.2 ppM, 7.5 ppM and 1.4% respectively. A number of these zones of increased concentrations show corresponding anomalous responses on the uranium/potassium and/or uranium/thorium pseudo-contour maps. Based on this set of computer printer maps alone however, it is, at times, difficult to discern the contribution of coinciding local decreases in the potassium and thorium parameters to these ratio anomalies. Based on the criteria stated in the general section on interpretation, a total of seven uranium and seven thorium anomalies have been outlined on the interpretation map. All of these features, described in Appendix B, exhibit only weakly to moderately anomalous responses. Due to the generally low radiometric levels encountered throughout the quadrangle along with the lack of any favorable indications for enriched accumulation of either uranium or thorium as seen in their radioelement distributions when correlated with the mapped geology and the weak, at best, evidence of preferential accumulations of either parameter, no follow-up work is recommended.