There is other option called Rotary drilling. This technique is inexpensive and fast and similarly to the reverse circulation drilling, there is some disadvantages such as samples are broken into small chips that don’t show the structure of the bedrock and the samples submitted for assaying are not very realistic. Most of the rigs are truck mounted and completely self contained, including the air compressor. Standard tri-cone bit can drill a hole four inches in diameter and the drill cuttings are blown out of the hole with compressor air. Samples are piled on the ground in rows, each pile represents approximately 0.50 to 3.0 meters of advance and each row from 6.0 to 30.0 meters of hole. Ideally, the sample must be collect in appropriate containers. This method is preferred by people who want to perform the sampling and logging in the same drilling hole.
Sometime, the drilling can be performed in two parts if the first program didn’t cover all the mineralized area. This additional drilling program can be complemented with geophysical methods in order to define the objectives of the program. For example, magnetic surveys identify magnetic zones that are related to silica cap areas. If the deposit presents high sulphidisation in areas far from the main ore body, the extra drilling is recommended. This can occur in deposits with structural and stratigraphic control and consequently some areas could be occulted. If the mineralization is close to the surface, at deeper areas may be or not possible to find high mineralization.
The drilling procedure can be designed under several considerations such as the geology team set out the holes in an area close to the drill rigs, drilling pads are done with bulldozers and the geologist oversee the work, cores are laid out for inspection, the final hole depth is decided by the geologists, hole location is recorded by GPS system, and geologist performs logging and coordinate the sample storage. There are other considerations that depend on the drilling target.
It is important to mark all drilled points