A Framework for Resolving Geotechnical Parameters in Hardrock Setting

A new framework resolving geotechnical parameters for hardrock environments has been established by linking seismic parameter (sp), bulk modulus (k), and density (d) in a 3D space. Conventional empirical relations (i.e Birch, Gardner, and Nafe-Drake) use a 2-parameter approach correlating seismic velocity and density. These relations prove compressional velocities do increase with increasing densities and this trend is observable, however, it only holds true for common crystalline rocks and not for high-density ores. Instead of a smooth trend as observed with silicate rocks, high-density materials, such as massive sulphides and Fe-oxides, are outliers and only exhibit a wide scatter distribution. Exploiting borehole seismic data (compressional and shear wave velocities), the new framework uses a three-parameter configuration of an elastic moduli (bulk modulus), density, and seismic parameter. Seismic parameter is defined as sp = Vp2 - (4/3)Vs2and is used as proxy for seismic velocities. In the d-k-sp space, all rock types project onto a single surface, including the high-density crustal rocks. Furthermore, the 3-parameter fit could hold as the basis for establishing calibration curves for ore materials of known hardrock environments (felsic, intermediate, to mafic setting) and in turn obtain elastic moduli and density from seismic data. Borehole logging is used extensively in mineral exploration to measure physical rock property contrasts and evaluate the quantitative link between geology and geophysics. A large dataset of over 2000 petrophysical measurements from laboratory experiments and multi-parameter borehole logging databases were used to provide the basis of investigating this new technique.