Summary

The Mira Geoscience Advanced Geophysical Interpretation Centre has completed 3D inversion modelling, integration, and visualization of airborne gravity, magnetic, and electromagnetic data for Central BC (including QUEST-West and Nechako), and integrating it with the QUEST and QUEST-South project areas. This was undertaken for Geoscience BC as follow-up analysis of geoscience data. The objective of this work is to provide useful 3D physical property products that can be directly employed in regional exploration to target prospective ground based on different exploration criteria.

This work considers all airborne gravity, magnetic and electromagnetic data available for the project area. The inversions were performed using the UBC-GIF GRAV3D, MAG3D, and EM1DTM, suite of algorithms for the gravity, magnetic, and AEM data respectively. The products are 3D inversion models of density contrast, magnetic susceptibility, and electrical conductivity, and integrated products combining the individual physical property models. In addition, detailed plate modelling of specific EM anomalies in several in-fill survey areas have been modelling using Maxwell discrete plates to provide a better interpretation where the target is less flat-lying in nature.

The gravity and magnetic data were modelled in 3D using several smaller tiles after separation of regional signal. The tiles for the QUEST-West and Nechako Basin areas were combined and merged with QUEST and QUEST-South models to construct a detailed model over the whole Central BC area.

The conductivity data were inverted for 1D (layered earth) models using a laterally parameterized method and subsequently interpolated in 3D. A late-time, background conductivity map has also been produced for the survey area. An estimate of the depth of penetration has been provided for the AEM conductivity models. The resulting models provide guidance to the regional structure and prospective geology and location of alteration and mineralization.

Final density contrast, magnetic susceptibility and conductivity models have been provided in different formats ready for 3D GIS analysis, interpretation, and integration with geologic, drillhole, and other geophysical information. The extensive set of digital deliverable products that accompany this report include: physical property cut-off iso-surfaces, observed and predicted data, and the inversion models in several different, commonly used formats. A suite of 3D PDF scenes have been produced to aid in visualization and communication.

The resulting physical property models can be used to guide regional targeting and help design more detailed, follow-up data acquisition. The inclusion of geologic or physical property information in the inversion from maps, drill-holes, and samples was not within the scope of this project, although it is expected that the integration of these data would improve the resulting models, especially at the local scale.

Results of the QUEST and QUEST-South inversion modelling projects were released by Geoscience BC as Reports 2009-15 and 2011-14 respectively.