Trenching is a basic but important exploration method used to find valuable minerals or materials in the ground. It involves digging long, narrow ditches (trenches) to expose and study underground rock layers and mineral deposits. This technique helps exploration companies determine if an area might contain valuable resources before investing in more expensive drilling programs. Think of it like cutting a slice in a cake to see all the layers inside. Companies use trenching as an early-stage exploration tool because it’s relatively low-cost and provides direct access to study the rocks and minerals below the surface [1].
Are commended procedure which has been found useful for sampling a trench is as follows [2]:
- Cut a continuous chip channel sample along the trench. The maximum size of the fragments should be around 50 mm. Any overlarge pieces will have to be broken with a hand-held hammer and the over break discarded.
- Lay a canvas sheet along the bottom of the trench to collect the sample.
- The sample volume is hard to control and will usually be too great for easy bagging. It must therefore be split to a smaller representative portion (say 5 10 kg) before it can be sent for assay. If the rock fragments are sufficiently small, this can be done using a riffle splitter. However, operating a splitter in the restricted area of a trench floor can be difficult, and cleaning the splitter between each sample is tedious and time consuming.
- An effective and less labour-intensive way of collecting a split for assay is to homogenize the sample by rolling it once or twice in the canvas tarpaulin on which it was collected, so as to form a long even pile of broken rock. The action is somewhat similar to rolling a cigarette but unlike a cigarette requires at least two people. A section of lengthways-cut 100–150 mm poly-pipe is then laid alongside the rock pile and by rolling rock and pipe together in the tarpaulin once more, the split pipe is filled with a portion of the broken rock pile. The contents of the half poly-pipe section can then be easily slid into a sample bag.
Reference
[1] “What is Trenching (in Exploration)? (for recruiters).” Accessed: Aug. 20, 2025. [Online]. Available: https://machinehiring.com/glossary/trenching
[2] R. Marjoribanks, Geological Methods in Mineral Exploration and Mining. Berlin, Heidelberg: Springer, 2010. doi: 10.1007/978-3-540-74375-0.
