By Gerry Mitchell, P.Geo, President PhotoSat
Accurate topographic mapping and surveying of a mining exploration project requires a significant investment of time and resources.
For early stage mining exploration project work, 3m survey accuracy is sufficient.
Early stage mining exploration project work:
- Geological mapping and outcrop sampling
- Geochemical surveys
- Geophysical surveys: magnetics, electromagnetics, induced polarization, gravity
Most early stage mining exploration projects require mapping quality topography, accurate to about 3m horizontally and 3m in elevation. This is similar to the accuracy of the hand held GPS units used by most exploration geologists to record geological observations and sample locations.
For exploration drilling up to the “discovery” drill hole, 3m survey accuracy is sufficient.
The initial exploration drilling will be focused on geological, geochemical or geophysical targets. Location of drill collars to 3m in XYZ is usually sufficient accuracy for the initial exploration drilling. Once there is a discovery drill hole, project focus shifts to the confirmation and delineation of inferred resources.
When drilling to delineate resources after a discovery drill hole, you need better than 50cm survey accuracy.
Once the focus of the drilling campaign shifts to confirmation and delineation of inferred resources, survey quality topographic accuracy is required for the project. This is accuracy of better than 50cm in XYZ for drill hole collar locations and the locations of surface samples and trenches.
First, establish a survey benchmark with GPS.
The first and most important step in accurately surveying an exploration project is establishing a survey benchmark that is accurate to better than 10cm in easting, northing and elevation. The most reliable way of establishing an accurate survey benchmark is to record 12 hours of GPS signals with a dual frequency geodetic quality GPS receiver. PhotoSat provides guidelines for establishing survey benchmarks.
GPS survey the drill hole collars, trenches and ground control targets.
The drill holes, trenches and at least three ground control targets should be surveyed with differential GPS. For differential GPS surveys, the GPS signals at the benchmark, and the survey point must be recorded at the same time. Many of the survey points can be surveyed while the benchmark survey is being recorded for 12 hours. The GPS signals at each of these survey locations should be recorded for at least 30 minutes plus one minute for each kilometer of distance between the survey benchmark and the survey location.
LiDAR, PhotoSat or Drone topographic survey of the project area
Depending on the size of the area, vegetation cover and location survey the project area to an accuracy of better than 50cm in elevation with airborne LiDAR PhotoSat or a Drone survey. The advantages of the different survey methods are discussed in a PhotoSat surveying white paper Comparison of PhotoSat, LiDAR, GPS and Drone surveying.
This survey will provide the topographic surface needed by the mining engineers preparing the reserve and resource volume calculations for your Preliminary Economic Assessment (PEA).