Integrated analyses of density, P-wave velocity, lithogeochemistry, and mineralogy to investigate effects of hydrothermal alteration and metamorphism on seismic reflectivity: a summary of results from the Lalor volcanogenic massive-sulfide deposit, Snow Lake, Manitoba

We present herein a summary of integrated data analyses aimed at investigating the effects of hydrothermal alteration on seismic reflectivity in the footwall of the Lalor volcanogenic massive-sulfide (VMS) deposit, Manitoba. Multivariate analyses of seismic rockproperties, lithofacies, and hydrothermal alteration indices show an increase in P-wave velocity for altered volcanic and volcaniclastic lithofacies with respect to their least-altered equivalents. Scanning electron microscopy-energy dispersive X-ray spectrometry analyses of drill-core samplessuggest that this P-wave velocity increase is due to the high abundance of high P-wave velocity aluminous minerals, including cordierite, Fe-Mg amphibole, and garnet, which in volcanic rocks are characteristic of VMS-associated hydrothermal alteration metamorphosed in the amphibolite facies. Aseismic synthetic profile computed from a simple amphibolite-facies mineral assemblage model, consisting of mafic-felsic host rock contacts, a sulfide ore lens, and a discordant hydrothermal conduit, show enhanced seismic reflections at conduit-host rock contacts in comparison to the equivalentgreenschist facies mineral assemblage model. Collectively our results suggest that VMS footwall hydrothermal alteration zones metamorphosed under middle- to upper-amphibolite facies conditions have enhanced potential for seismic detection.