Subsurface rock interface imaging with the application of Ground Penetrating Radar (GPR)

ABSTRACT: In this study, ground penetrating radar (GPR) data were collected in field trials both on the surface and downhole. The target of this study is to evaluate the possibility of the identification of the rock interface between gold ore and surrounding rock using borehole GPR. The basic theory of GPR was reviewed before the trials. In surface field trials, the GPR data were collected to identify the rock interface between shale and limestone in a quarry and to identify the rock interface between basalt and rhyolite in cripple bay. In the downhole field trials, the GPR antenna was put in the borehole in the mining site. The GPR imaging result was analyzed with the consideration of the field geometries. Then, the penetration depth and the ability to identify the subsurface structure was evaluated. According to the result, GPR units with the center antenna frequency of 1GHz presents a smaller penetration depth than 250MHz GPR, which is 2.5m for surface imaging in homogenous material and 1.8m for downhole imaging. Primary reflections are collected in the results and concur with the field geometries. This study also revealed some problems. The fast traveling speed of the antenna reduced the noise cancelling efficiency and influenced the imaging quality. Unexpected reflections found in the result, which may be a result of a lack of understanding of the field geometry. Overall, 1GHz GPR showed its potential in the downhole imaging application and further work should be done to improve the quality and accuracy.