Multiparameter petrophysical characterization of an orebody: an exploration case history

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Emmanuel Bongajum, Isabel White, Bernd Milkereit,
Abstract We present results from petrophysical studies to characterize a large Zn-Pb-Ag deposit in New Brunswick. The measurements are part of an integrated study that includes geological and geophysical data acquired on the property. In order to successfully characterize the ore body, we need to understand how the physical parameters and assay data provide information on the vertical and lateral variations of the lithology especially that of the target. The quality of the estimated 3D variation in the physical properties is supported by the presence of several boreholes that randomly span the survey region. Density was measured from cores of thirty-two boreholes across the area. Seventeen of these boreholes constitute two intersecting borehole profiles, which is ideal for locally modeling the 3D distribution of the ore deposit. High density (>3.2g/cm3) correlates strongly with low resistivities (<15ohm.m) obtained from vertical resistivity profiling (VRP). This high density and low resistivity corresponds to Zn-rich mineralization. Compression and shear wave velocity measurements made from representative core samples of the regional geology range from ~2.91 to ~6.41 km/s for P-waves and from ~1.41 to ~4.20 km/s for S-waves. The lower bounds of these velocity values correspond to regions with a high degree of alteration. Moreover, porosity estimates from rocks on the property suggest that porosities range from very low porosity (0.006) to very high porosity (0.2). Core samples with high mineralization show very low values of magnetic susceptibility, suggesting potential difficulties in mapping the ore deposit with magnetic methods. Induced polarization (IP) measurements confirm that mineralized samples have a sharp chargeability contrast with respect to the host rock. Chargeability can thus be used as a basis for identifying conductors associated with mineralization in electrical survey data.
Information on these physical parameters and their 3D statistical distribution have serious implications in various aspects of mineral exploration that include: resource estimation, choice of geophysical data acquisition and interpretation, and information for preliminary rock stability assessment.
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