Gpr Technique Applied To Mineral Exploration Of Geodes In Basalts: Amethyst Geode Deposits (Rs, Brazil)

Geodes in basalts are not simply a void problem. The<br>amethyst geodes are hosted by a massive, poorly<br>fractured basalt. Amethyst geodes range from 0,1 to<br>1,0 m in diameter, and are variably filled with<br>different paragenesis. GPR technique does permit<br>imaging amethyst geodes and other structural features<br>based on contrasting electrical properties of materials.<br>GPR imaging resolution, penetration and wave<br>propagation image features depend on EM wave<br>frequency. High frequency EM wave (800 and 1000<br>MHz) has low penetration and high resolution, and<br>they are suitable for amethyst geode detection, even<br>the reflection and diffraction pattern produced. Low<br>frequency EM imaging (250 MHz) imaging for<br>amethyst geode can display reflection and diffraction<br>pattern similar to that defined for high frequency<br>ones, but can also image fracture systems crosscutting<br>host basalts. These radargrams patterns can be used<br>mainly for amethyst exploration and extraction planning.