Theoretical studies of in‐situ rock density determinations using underground cosmic‐ray muon intensity measurements with application in mining geophysics

Abstract

The feasibility of in‐situ rock density determinations by means of subsurface cosmic‐ray muon intensity measurements is based on theoretical calculations for two hypothetical scintillation counter telescopes: one is intended for registration in a gallery and the other is intended for use in narrow boreholes. It is shown that it is possible to measure the mean density of the rock traversed by the muons by measuring the muon intensity. The sensitivity of the method is favorable—a 1 percent change in mean rock density corresponds to a change of about 3 percent in the counting rate. A possible use of cosmic‐ray muon technique is the localization of an anomalous density distribution in overlying rock. A characteristic minimum registration time to detect a certain density anomaly varies from a few hours to about 10 days, depending on the geologic situation and the depth and design of the detector. The device is found to be most applicable for massive sulfide and iron exploration. This tecnique provides some new possibilities. A certain spatial resolution can be achieved at the expense of the registration time, and the overlying rock can, to some extent, be investigated in different directions from one point of observation. The method seems to be useful down to depths of approximately 600 m for the gallery application and 400 m for the borehole application. However, these limits are a consequence of the size of the detector, the size and density contrast of the target, and the maximum registration time accepted for each observation.