MODES: AREAL MAPPING AND DEPTH SOUNDING
A comprehensive PMRSE field survey is achieved by a combination of two survey
modes: areal mapping and depth sounding.
While mapping allows exploring subsurface objects in plan, soundings allow
exploring subsurface objects in a vertical perspective.
The PMRSE mapping is
a process of delineating the boundaries of distribution of the substance of
interest and is performed by way of intersecting surveyed objects along profiles.
The distance between survey profiles depends on details required and
accessibility of the territory. The frequency of records on the profile depends
on the speed of movement. When moving along profile one operator can make
records of one parameter at a time. Usually this is the content of the substance
of interest. By performing mapping of the area it is also possible to trace
tectonic faults, caverns,
contacts of rocks, etc.
When doing the mapping the work
productivity depends on exploration details required and a vehicle used. If
exploring afoot, in 1 working day one operator can cover the grid of profiles
total 6-8 km long taking readings for one parameter. Using a car such
measurements can be performed on the grid of profiles total 100-150 km long.
The results of mapping allow
plotting areal maps of mineral deposits or plumes of chemical contamination of
underground water or soils in form of projections on the daylight surface or in
form of slice-maps at a set depth. A PMRSE map of chromite ore
deposits at a set depth is presented as an example on the left.
The PMRSE depth sounding,
as a standard well log, allows exploring subsurface objects vertically or at an
angle but the method does not need well drilling. The step/interval for signal
measurements down the "hole" can vary from 10 cm to 1 m depending on details
required to the depth of 5000 m.
The resolution and the minimum step of measurements during soundings depend on
the resonance wavelength of the objects of concern as well as resonance
properties of the antenna.
With each step of measurement the substance content is measured in the rock
column 10 cm in diameter and from 1-2 cm to a few decimeters in height depending
on the resonance frequency of the surveyed substance.
During soundings all the measurements are discrete but when the measurements are
performed with a resonance wavelength ratio taken into account, the technology
can provide a continuous description of the geologic section.
Each selected location is usually surveyed for a number of parameters. To get a
complete description of the geologic section the obligatory parameters for
measurements are density of rocks in their natural occurrence, content of two or
three rock-forming minerals and possibly moisture of rocks – for layering the
cross-section, determining the watering of rocks and a possible
position of the mineral(s) of concern.
Additionally, the measurements of content of the substances of concern are
carried out to the whole exploration depth or in a set depth interval. The
substances of concern can be any kinds of minerals in exploration projects and
chemical compounds of a technogenic origin in environmental projects.
When doing vertical soundings the work productivity depends on the step of
and the number of parameters
When measuring one parameter with the step of 10 cm one operator in 1 working
day can perform
up to 1000 running meters of
When measuring one parameter with the step of 1 m one operator in 1 working day
can perform up to 10,000 running meters of soundings.
Taking into account at least 4-5 parameters usually measured at one location,
one operator in one day can perform a comprehensive sounding with the step of 10
cm to the depth of 250 m and with the step of 1 m to the depth of 2500 m.
The results of soundings allow
lithologic columns, geologic sections, structural maps, maps showing bedding
depths of underground water and other geologic models.