Mid-Atlantic Iron Belt Project -
Phase 2 -
Rittenhouse Gap Geophysical Reconnaissance Survey
Four undergraduates student involved:
- Richard Orner (junior)
- Bob Hopkins (junior)
- Kerk Halberg (junior)
- Laurel Black (sophomore)
Project: Using
GPS integrated with a laser surveyor to determine precise locations of
measurements, students used a proton precession magnetometer and gamma
ray spectrometer to measure the intensity of the magnetic field and the
gamma emissions of basement rocks beneath thick soil cover. The
intensity of the earth’s magnetic field is locally affected by the
presence of magnetic minerals in rock. Gamma rays are emitted
from rocks as minute amounts of radioactive isotopes that are present
in all rocks decay. The intensity of different types of gamma ray
emissions translates directly into the concentrations of potassium,
uranium, and thorium in the rock. Measurements were made along
two 80-meter long linear traverses spaced every two meters.
Because the magnetometer, GPS, and gamma ray spectrometer can
potentially interfere with each other’s measurements, we required a
3-4-person team for data collection to keep the devices separated by a
safe distance.
Results: Although
gamma ray data did not have a recognizable pattern, possibly due to
varying thickness of soil cover “shielding” gamma emissions, the
magnetic data clearly demonstrated that we could successfully identify
the locations of magnetite veins buried beneath the forest
litter. Laser surveying was successful for determining sample
location because tree cover blocked GPS signals, although the close
spacing of trees prevented long distance shots. We concluded that
standard GPS techniques would be quicker if we made measurements late
in the fall or in winter when tree canopy was clear.
