Summary

Airborne time-domain electromagnetic (EM) data were collected in 2012 over the Caber volcanogenic massive sulfide (VMS) deposit in western Quebec. We inverted the data in three-dimensions (3D) to produce a conductivity inversion model that helped image the thin dipping conductor and surrounding geology. The 3D inversion method consisted of a two-step approach. The first step employed a parametric inversion to recover a best-fitting shape of the dipping conductor using only data exhibiting an anomalous response over the deposit. With the parametric result as an initial and reference model, the second step used a conventional 3D EM inversion with data locations over the entire survey area. The second stage allowed for fine tuning of the shape and conductivity of the central dipping anomaly, while filling in features, such as overburden, in the remaining areas of the domain. The shape of the central conductive anomaly in the 3D inversion compared well with the known outline of the Caber deposit, based on geologic knowledge from past drilling. The overburden layer in the inversion model also agreed with previous geologic mapping. Preliminary results from this two-stage process show that it possible to recover a thin, dipping conductor with sharp boundaries through 3D EM inversion, which has been a difficult challenge in recent years.

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