TRENCHING AS USED IN GEOLOGICAL EXPLORATION

_{Taking some readings within trench}

WHAT IS TRENCHING?

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Trenching refers to the cross-cut session of the earth and it is done to pick lithology types, identify structures, and assay values. Trenches are done in shallow areas. This means that they are done in areas where the over bedding cover is less than 3 meters thick.

Also, in deciding our area for trenches, we need to consider the behaviour of our mineralization. Where mineralization is steeping, we do trenches and where they are flattening, we do pitting. This is because we want to have get a cut section of the earth and see how the structures are behaving.

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_{Typical Example Of A Trench}

PROFILING THE TRENCH

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The trench is such that it was planned to be perfectly horizontal but in reality, we may not be able to achieve this. As such in profiling, we are interested in obtaining a reference point from where our readings are going to be taken. This reference point needs to be horizontal so with the aid of a spirit level, we use a nail to demarcate our points and a rope to tie around it. This means that we will take our readings with respect to these reference point.

This done for various intervals and where the rope seems to be nearing the ground, we introduce a change in elevation so we can proceed. Where the elevation is increasing upwards, it is positive and where it is going downwards, it is negative.

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PROFILING THE TRENCH

The steps involved in profiling can be seen below;

• Hammer a nail at the start of your profiling at depth 0m.
• Tie a rope around it and stretch it horizontally with the help of a spirit level. 7
• Ensure that it doesn’t lean against the trench wall.
• As it nears the ground, we introduce a change in elevation and then continue from there.
• The change in elevation is noted and then indicated as well.

_{Profiling of Trench within the Ashanti Region}

TRENCH SAMPLING

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Trench sampling is done so that we can know the specific composition of various elements within the trench. Here, we sample across the trench at various intervals. And in sampling the trench, we make sure that priority is given to the alteration zones or shear zones.

This is because, these are the areas we expect to find mineralization. We do 1 meter or 2 meter sampling of areas of the same lithology or rock mass till we reach different lithology such as an intrusion, shear zone or alteration and then we sample that one alone. This is because, these are the areas we are most interested in.

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After samples have been collected, they are sent to the lab to be examined and interpretations are made based on the elements of interest.

Thank you for your attention.