In-mine seismic delineation of mineralization and rock structure

Significant progress has been made towards the goal of generating detailed seismic images as an aid to mine planning and exploration at the Kambalda n ickel mines of Western Australia. Crosshole and vertical-seismic-profiling instrumentation including a slimline multielement hydrophone array, three-c omponent geophone sensors, and a multishot detonator sound source, have bee n developed along with special seismic imaging software to map rock structu re. Seismic trials at the Hunt underground mine established that high frequency (>1 kHz) signals can be propagated over distances of tens of meters. Tomog raphic as well as novel 3-D multicomponent reflection imaging procedures ha ve been applied to the data to produce useful pictures of the ore-stope geo metry and host rock. Tomogram interpretation remains problematic because ve locity changes not only relate to differing rock types and/or the presence of mineralisation, but can also be caused by alteration/weathering and othe r rock condition variations Ultrasonic measurements on rock core samples he lp in assigning velocity values to lithology, but geological assessment of tomograms remains ambiguous. Reflection imaging is complicated by the prese nce of strong tube-wave to body-wave mode conversion events present in the records, which obscure the weak reflection signatures. Three-dimensional re flection data processing, especially three-component analysis, is time cons uming and difficult to perform. Notwithstanding the difficulties, the seism ic migrations at the Hunt mine show a striking correlation with the known g eology Combined seismic and radar surveying from available underground bore holes and mine drivages is probably needed in the future to more confidentl y delineate mineralisation.