Converted wave seismic imaging in the Flin Flon mining camp, Canada

Abstract

Abstract Seismic imaging for mineral exploration in hardrock environment has typically relied on P-waves recorded using vertical component geophones. Here we demonstrate the potential of using P-to-S converted waves for mineral exploration by applying converted wave processing to high-resolution 3-component data acquired in the Flin Flon mining camp, Canada. Inferences regarding the relative value of PS data are made through comparison with corresponding PP images, interpretation with geological constraints, and by comparison with modeling results. Modeling results show that the horizontal component data provide a robust means of separating the PS conversions from the PP reflections in converted wave processing whereas contamination by PP energy is more severe if the vertical component data are used. A customized processing workflow has been developed in which horizontal component data are sorted into common-reflection point gathers by the application of the converted wave dip-moveout operator. The PS images are characterized by lower signal-to-noise ratios than the PP images due to the smaller S-wave impedance contrasts associated with the main lithologic units and the angular dependence of P-to-S conversion. An exception to this occurs for PS reflections from the ore zones which are accentuated on the PS images relative to the background host-rock reflectivity. There are discrepancies in the reflection dips and positions observed on corresponding PP and PS sections that are not fully explained. They can be partly attributed to the non-coincidence of subsurface spatial sampling associated with common-depth points versus common-conversion points, with an additional complication associated with the known 3D geology. Vp/Vs ratios determined by correlation of reflections observed on PP and PS images can provide a limited means of lithological discrimination.