Integrated Geological & Geophysical Porphyry Models: Adding Value to Geoscience BC Geophysical Data (NTS 93E, 93K, 93L, 93M, 93N)
- Dianne Mitchinson, MDRU

To interpret geophysical data most effectively, it is necessary to have an understanding of the characteristic ranges of physical property values of the rocks being surveyed. With knowledge of how physical rock properties vary with rock type, hydrothermal alteration, and mineralization, it is also possible to constrain geophysical inversion calculations to refine 3D models of the Earth's subsurface. This Geoscience BC funded project aims to 1. compile existing property data from rocks representing a selection of central BC mineral deposits, 2. enhance the physical property database with new property measurements made on samples from these deposits, as well as from rock samples collected from outlying areas, and 3. apply acquired property knowledge to constrain geophysical inversions. The mineral deposits being investigated are those over which Geoscience BC had detailed magnetic and EM surveys flown as part of their QUEST and QUEST-West projects. They represent mainly porphyry-style deposits, and include past producers, current producers, and projects in development stages.

Selected Mineral Deposits in Project Study
Initial work will involve compilation of four types of rock property data: magnetic susceptibility, density, conductivity, and chargeability. These are the rock properties that correspond to magnetic, gravity, electromagnetic/DC resistivity, and induced polarization geophysical methods, respectively. This data will be statistically analyzed, and mineral analyses will be completed to identify the primary and secondary geologic processes controlling each of the properties. The mineral deposits focused on showcase a range of host rocks and alteration styles, and physical property studies will involve a comparison between behaviors of rock properties in the various settings represented. Unique property ranges found to be associated with mineralized rocks will be sought.

The second phase of the study involves using physical property knowledge to constrain geophysical inversions. Geophysical inversion, the calculation of a subsurface physical property distribution from collected geophysical data, yields improved models when prior geological and physical property information is considered. Downhole property measurements, such as magnetic susceptibility measurements can be directly input as control points. General physical property knowledge, such as expected ranges of property values for certain rock types or altered zones can also be used to guide inversion results. For this second stage of the project, there will be close collaboration with Doug Oldenburg of the Geophysical Inversion Facility (GIF) at the University of British Columbia in assembling all available geological, geophysical, and physical property information, and throughout forward modeling and constrained inversion work.

The physical property data compiled as part of this project, and the geophysical case study demonstrations will serve to aid BC geoscientists in planning geophysical surveys, interpreting geophysical data, and improving subsurface geology models in similar geological settings in BC.

Posters and Presentations
2013: Linking Physical Rock Properties to Porphyry Alteration and Mineralization: Examples from the QUEST and QUEST-West Project Areas
- Mineral Exploration Roundup Presentation (pdf, 4 MB)

2011: Physical Property-Geology Relationships in Porphyry Deposit Settings in Geoscience BC's QUEST and QUEST-West Project Areas, Central British Columbia
- Mineral Exploration Roundup Poster (pdf, 4.6 MB)

2010: Enhancing Geophysical Interpretation and Mineral Deposit Modelling Through Knowledge of Physical Rock Properties: Magnetic Susceptibility Studies for Porphyry Deposits in the QUEST and QUEST-West Areas (NTS 93E, K, N)
- Mineral Exploration Roundup Poster (pdf, 7.68MB)
Technical Articles
2011: "Continued investigations of physical property–geology relationships in porphyry-deposit settings in the QUEST and QUEST-West project areas, central British Columbia"
- Summary of Activities 2010, Report 2011-1 p.17-32 (pdf, 12.9 MB)

2010: "Enhancing geophysical interpretation and mineral deposit modelling through knowledge of physical rock properties: magnetic susceptibility studies for porphyry deposits in the QUEST and QUEST-West areas (NTS 93E, K, N)"
- Summary of Activities 2009, Report 2010-1 p.53-64 (pdf, 6.0 MB)

Final Deliverables
Geoscience BC Report 2013-14
Linking Porphyry Deposit Geology to Geophysics via Physical Properties: Adding Value to Geoscience BC Geophysical Data

This report presents physical rock property data from six BC porphyry deposits (Mount Milligan, Endako, Huckleberry, Bell, Granisle and Morrison) and discusses observed trends within the detailed QUEST and QUEST-West geophysical datasets and mapped geology. The resulting physical rock property data compilation has implications for improving interpretations of geophysical data from porphyry deposits. A synopsis of physical property criteria defining hydrothermally altered or mineralized rocks in BC porphyry settings is provided, which can ultimately be used for ranking similar mineral exploration targets throughout BC, thereby minimizing exploration risk.

 


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