- geophysical contract negotiations (survey design, data quality, deliverables and accountability)
- geophysical survey design and pre-survey modelling where applicable
- geophysical data acquisition Quality Control for airborne or ground surveys
- contractor supervision and management
- data QA/QC, compilation, processing and visualization (2D & 3D)
- historical data organization, compilation and re-interpretation
- data modelling in 2D & 3D using WinDisp & MGinv3D for MAG and GRAV data
- data modelling using Geosoft VOXI cloud-based 3D inversion code for MAG, GRAV and IP/Resistivity
- data modelling in 2D IP/Resistivity inversion using UBC DCIP2D v5 code
- Maxwell EM plate modelling
- data visualization, interpretation, target selection and follow-up recommendations
- data compilations are conducted in Geosoft Oasis montaj and Discover PA (Encom Profile Analyst). Geosoft work is delivered as a complete project file that is accessible through the free Geosoft viewer.
- drill program targeting
- program management of both ground and airborne geophysical surveys
- internal or remote presentations and planning sessions
Pre-survey planning is essential for geophysical programs. This begins with contract negotiations and ensuring that the survey type and design are best suited for your exploration needs. Contract negotiations are often overlooked. Data acquisition parameters with respect to measurement tolerances are an important consideration. Data modelling can be conducted in order to refine survey parameters and confirm that a target of interest or conceptual model will be appropriately delineated. Target detection and delineation are not necessarily the same. Clearly defining survey objectives is crucial. Choosing the correct survey type is also a key first step.
- Is your target known or conceptual?
- Are there any target variations? Could aspects of the conceptual model be missing?
- What are the defining characteristics of the model in terms of physical rock properties?
- How do rock properties such as magnetic susceptibility, density, resistivity, porosity and gamma radiation factor into your target model?
- Is your target amenable to direct detection through mapping physical rock properties or would geologic mapping be a contributing factor to further exploration?
- Geophysical measurements are directly related to geology, mineralization and alteration.
- Successful geophysical surveys require that physical rock property contrasts be large enough to be measurable from either ground or airborne surveys.
- Target size, depth, geometry and amplitude of rock property contrast are key factors in detectability.
- What is the role of alteration and its effect on rock properties? Is there evidence of magnetite destruction?
- Are multiple survey types required in order to maximize geologic mapping and direct detection?
- Survey design takes into account known information as well as conceptual ideas.
Geophysical surveys are a long term investment and data quality is critical for confidently interpreting the results. Data review and QC is an essential aspect of any geophysical survey. It is ideal to perform data QC during data acquisition rather than after a survey has been completed and the survey crew has demobilized. QC or review should also be conducted soon after receipt of final data to confirm that data quality and positioning is as it should be. It’s unfortunate, but sometimes final data is not final.
Data visualization is a key component of building a data compilation. Numerous enhancements can be achieved from individual data sets or combinations. For example, ternary images which are a common product in radiometric surveys are also useful or revealing geophysical domains from other data sources such as magnetics, gravity or electromagnetics. The first two images show a ternary image of magnetic data and automated lineament interpretations based on CET lineament analysis and USGS curvature analysis. The third image illustrates enhancements of magnetic data (original data shown on the left). Image descriptions are included as captions for the remaining images.
Geophysical data modelling is performed in either 2D or 3D. 3D inversion modelling of magnetic and gravity data is conducted using MGinv3D inversion code (Scientific Computing and Applications) or Geosoft VOXI cloud-based on-demand modelling. 3D EM plate modelling is conducted using Maxwell. 2D modelling for IP and Resistivity utilizes UBC DCIP2D version 5 code. 2D modelling for magnetics and gravity is performed using WinDisp.
Data interpretation is a process that benefits from collaboration between geoscience disciplines. Geophysics data can be interpreted in isolation, at times there could be justification, but ideally geophysical interpretation should be conducted alongside geologic and geochemical data. Image 1 is an example of a target compilation summarizing all available data. A PDF document is created for each target. Image 2 illustrates presentation variations of radiometric elements used in interpretation. Image 3 suggests that sometimes it’s better not to interpret “solid lines or features”, but rather highlight a feature of interest and allow the observer to see it for themselves. If outlines had been drawn on this image it would have obscured a subtle outlines of these regional features. Suggesting where to look helps the observer to confirm it for themselves. There are possibly two more ovoids that have not been outlined in this image.
An interpreters natural tendency is to look for targets in regions of known mineral showings. This is not a bad thing as “closology” often works very well. However, it is important to understand and be aware this bias (keeping in check that it is possible to see what we want or hope to see) as well as being willing to think outside the near-mine scale. Exploration targeting generally takes multiple passes through integrated data sets. The more data are integrated, the better they can illuminate conceptual models and minimize the inherent risk in exploration. It is important to root one’s thinking in the mechanics of mineral systems. How did they get there? By what processes? What are the by-products and how do they affect rock physical properties such as susceptibility (i.e. magnetic mineral destruction due to chemical and thermal alteration effects), resistivity/chargeability and density.
Explorationists should consider that all traditional components of generalized deposit models may not be present in all instances; how will this affect targeting? Geoscience data integration promotes a collaborative working environment: geologists help guide geophysicists efforts by helping to constrain and promote interpretations within the realms “geologic” reality and providing straightforward geologic models that can be attributed to rock property contrasts and geophysicists support geology and geochemistry with the ability to help map geology and alteration by connecting the dots within their data sets and allow them to target at depth and undercover.