oa Rock Mass Characterization Using Geophysics For Stope I,Eaching

The Bureau of Mines is researching the feasibility of in situ stope<br>leaching for active underground metal mines. A test facility was<br>developed in an underground mine near Idaho Springs, CO, to<br>investigate the processes of leaching solution control. An<br>important aspect of the research is the characterization of the<br>rock mass in terms of discontinuities which will determine fluid<br>flow and affect fragmentation from blasting. Geologic mapping and<br>core logging documented the fracture and joint systems in the<br>simulated stope and adjacent areas of the underground facility.<br>Slimline borehole geophysical logs were used to verify lithologic<br>changes and indicate locations of fracture zones. Conventional<br>and full wave form sonic (FWS) logs were obtained, where<br>possible, to interpret fracture zones and define optimum<br>locations for permeability tests. In addition, sonic shear wave<br>profiles were obtained with a wall-clamping probe in the<br>boreholes drilled at the site. Shear wave measurements were not<br>as sensitive to fracturing as the conventional travel time P-wave<br>logs, but the capability for dry hole operation provided data in<br>zones of the rock mass that would otherwise be unavailable.<br>Integrated interpretation of the geophysical logs enhanced the<br>geological characterization of the in situ rock mass by<br>distinguishing open fractures (possible fluid conduits) from the<br>closed fractures. Estimates of the dynamic elastic moduli<br>provided a baseline for comparison of post-blast measurements to<br>evaluate overbreak and control solution loss during the leaching<br>phase of the experiment. Cross-borehole sonic surveys and<br>tomographic imaging were also demonstrated effective in<br>correlating the fracture zones between drillholes.