Preliminary exploration can be performed by trenching. This method needs a backhoe or bulldozer, which makes possible to observe and take bulk samples on a continuous basis across the mineralized zone. Several ore types are weathered easily at the surface and these layers have to be removed in order to have good information on mineralogy and lithology. Preliminary trenching and pitting may be done with the objective of providing initial information to geologists in order to improve the parameters estimated for this sampling program.
Different rock layers are detected by trenching
Normally, trenches are excavated by hand employing picks and shovels until the bedrock is visible, most the time at depths of 1 to 3 metres. Trench sampling can be carried out by channelling a sample along the floor of the trench. Each channel is between 10 to 20 cm wide and 5 to 10 cm depth. Samples are taken for geological purposes. In this way, veins, altered zones or different mineralized zones can be sampled so that the contacts can be 2-4 cm within the sample boundaries. Sample weights are usually between four to eight kilos.
In serious and big trenching programs, bulldozers are employed to explore the different areas at different depths. That kind of equipment is easily available when is necessary to move huge tonnes of waste material to access the place. Mechanical or hydraulic rippers are employed in difficult mineralized zones. If extra depth is required, a shallow shaft is sunk at lower cost and with less damage to the surface. The face or uphill side of the trench is a zone of geological information and sampling point due to these zones are virgin and clean of broken material. Trenching programs are useful when they are planned properly, but they could be a waste of money and time when the program was prepared without technical considerations.