JORC, NI43-101, SAMREC, etc. guidelines used by the company undertaking the drilling campaign may require the mining company to complete drilling following either methodology (DD or RC) to ensure samples collected are representative for assay.
RC and DD drilling techniques are distinguished in several important ways:
Context of use
Diamond drilling is used for very precise sampling where: relationships between geological units (contacts between sequences, veins) and analysis and angular measurements of structures are important. Reverse circulation is used for bulk sampling where a broad definition of ore bodies and geochemical analysis is important.
Nature of the sample
In the context of RC drilling, rock chips called cuttings are obtained, while in the case of DD drilling an intact sample is obtained. Cuttings are intended more for geochemistry while cores from diamond drilling are used to perform structural measurements, evaluate the quality of the rocks and conduct geotechnical studies.
Drilling speed
The rate of advance in DD drilling is slow and variable depending on the type of rock as well as fracturing. This speed is greater with the RC method.
Depth capacity
RC drilling can go up to a maximum of 800 m while with large capacity machines DD drilling can reach 3000 m.
Hole diameter:
✓ DD drilling: 46 to 146 mm
✓ RC drilling: 89 to 146 mm.
These diameters depend on the tool used.
Cost
DD drilling requires a low initial investment but is more expensive per drilled metre due to the speed limitation; approximately €30 to €100/m while RC is certainly expensive initially but with the speed, the cost price per drilled metre is between €20 and €50, assuming that a booster is not used.
