The branch of geology that deals with the form, arrangement, and internal structure of rocks, and especially with the description, representation, and analysis of structures, chiefly on a moderate to small scale is called Structural Geology.
What to understand?
It is of paramount importance for the geologist and mining geologist to characterize the orientations observed in the field. Also, remember that whatever the observed structure, its shape can be reduced to the classic forms of the plane or line. Thus, in practice, it is sufficient to measure the spatial orientation of a line in the field to be able to characterize that of a geological structure.
Some definitions
Plane strike: This is the spatial position of its horizontal. The horizontal being the intersection between the plane in question and a fictitious horizontal plane.
Trace: From the structural geology perspective, this is the line obtained by the intersection of two planes.
Azimuth of the LGP: This is the angle between the direction of North and the projection of the line of greatest slope onto the horizontal plane.
Azimuth of the line: This is the angle measured between the direction of North and the down-dip direction of the line.
Pitch or dip angle: This is the acute angle measured between the horizontal of the plane bearing the line and the line itself.
Descriptive methods
In structural geology, it is fundamental to remember that there are 04 types of representation modes.
- Representations by blocks made in 3D by drawing such as the example of block diagrams;
- Cartographic representations such as geological maps and structural maps;
- Cross-section representations;
- Stereographic diagram representations.
Measuring equipment: compass and clinometer
The compass and clinometer allow for the measurement of the orientation of a plane. The compass is graduated from 0 to 360° clockwise (internal graduation). The clinometer, on the other hand, is at 180° with two internal subdivisions that vary from 0 to 90°. A good compass must contain a clinometer at the same time.
Importance of taking structural measurements
Taking structural measurements is of paramount importance for a geological and mining engineer.
It allows in general geology to identify the cleavage planes of rocks. Also, to characterize the various geological structures outcropping. It also allows to define the preferential orientation of minerals and thus to understand the various geological phenomena that have affected the rock in place.
In rock mechanics, it allows to define the major direction of discontinuities in a massif and thus to predict the results of future mining in relation to the orientation of the boreholes.
