The airborne geophysical survey covered a 6,127 square kilometre area stretching from Port McNeill in the north to Tahsis in the south, covering portions of the Regional Districts of Strathcona and Mount Waddington. It did not include Woss Lake, Nimpkish Lake or Schoen Lake Provincial Parks.
How Was the Data Collected?
The project was announced in March 2019. Following requests for feedback from the mineral development sector, community leaders and Indigenous groups, the helicopter survey was flown from August to October 2019.
The airborne geophysical survey collected information about the magnetic properties of the rocks below the ground and the radiometric properties of rocks and soils near the surface.
Precision GeoSurveys, the contractor selected to fly the airborne geophysical survey, began flying one helicopter over the survey area in early August 2019 from Port McNeill and from Woss. The helicopter was easily identified by three ‘booms’ containing magnetic sensors – one on each side and one at the front. It flew along lines spaced 250 metres apart and at a constant height of 80 metres, rising to 300 metres over communities. It did not fly over larger parks.
The magnetic survey mapped out the rock units below the surface that contain magnetic minerals, mostly magnetite, but also the iron oxide minerals hematite, maghemite, limonite, and some sulphide minerals such as pyrrhotite. These minerals disrupt the Earth’s magnetic field, and the magnetometer connected to the survey helicopter measured these subtle variations in the Earth’s magnetic field.
The results of the magnetic survey can help geologists understand the structure of the rocks several kilometers below and identify areas that are worthy of further investigation.
The radiometric survey mapped the distribution of naturally occurring radiometric isotopes in rocks and soils within about 30 centimetres of the Earth’s surface. As potassium, uranium and thorium naturally decay, they release gamma rays with characteristic energy signatures that the survey equipment attached to the helicopter detects.
The results of the radiometric survey can be used to update geological maps and, in some cases, may be used to directly detect mineral deposits.