- Created by: beth_brown29
- Created on: 14-03-17 13:19
Gravity surveys are a GEOPHYSICAL TECHNIQUE.
Differing densities of rocks/deposits cause small variations in the Earth's gravitational field. Measured using GRAVIMETERS.
Positive anomalies may indicate large metal deposits as metal minerals have a higher density than the surrounding rocks.
Negative anomalies can indicate granite intrusions and lead to finding hydrothermal veins.
Measured using a MAGNETOMETER. Surveys can be done on land or from air.
Magnetic anomalies are often caused by the presence of iron rich deposits.
Metal deposits conduct electricity better than the surrounding rocks = lower resistivity.
Survey is done by placing electrodes in the ground and passing electricity from the one to the other through the ground, a machine shows how much resistance was shown. After this the electrodes will be moved further away from eachother and repeated.
The more distance between the electrodes = the deeper the electricity flows and shows the amount of resistivity.
This can also be used for groundwater.
STREAM SEDIMENT SURVEY
This is a GEOCHEMICAL TECHNIQUE.
Geologists collect samples from the streams/rivers etc. They are analysed to measure the concentrations of metals. The researchers then make their was up stream or downstream, whichever way the concentrations get higher, to find the metal source.
DILUTION occurs downstream due to the gradual addition of sediment which does not contain the metal ore.
CATASTROPHIC DILUTION occurs where tributaries meet.
Sampling soil geochemistry on a slope can pinpoint a mineral vein.
Vegetation type and the colour of the soil can also indicate the presence of minerals.