Diamond core drilling, or rock coring is definitely the best method for finding these deposits and the only way to retrieve bedrock samples, of varying sizes, usually five or ten foot long samples at a time. The process of rock coring is fascinating and done surprisingly quickly with modern day tooling and technology.
The use of a diamond encrusted drilling bit, water and high speed rotation, you can advance the casing or core into the bedrock. Watch this video of a diamond core drill, drilling bedrock from ground surface. The sample of rock is collected in a inner tube seated in the core barrel, which cab be extracted with the use of a wire line winch. This core sample is an undisturbed sample of the bedrock.
With high speed rotation and water as a flushing agent, as well as to cool the bit, the drill produces a "core" sample which then is extracted from depth, for examination. Geological site investigation is common in any area for studies of the Earth's formation or fractures in the earths rock layers. Environmental Site assessments are done by installing monitoring wells in the bedrock for future studies for water tables. Exploration diamond drilling is used in the mining industry to probe the contents of known ore deposits and potential sites. By withdrawing a small diameter core of rock from the ore body, geologists can analyze the core by chemical assay and conduct petrological and mineralogical studies of the rock.
Here is a chart showing the diameter sizes of which the rock is cored. Most rock coring tubes are in lengths of ten feet, but can also be done in five feet.
| Size | Hole (outside) diameter, mm | Core (inside) diameter, mm |
|---|---|---|
| AQ | 48 | 27 |
| BQ | 60 | 36.5 |
| NQ | 75.7 | 47.6 |
| HQ | 96 | 63.5 |
| PQ | 122.6 | 85 |
| CHD 76 | 75.7 | 43.5 |
| CHD 101 | 101.3 | 63.5 |
| CHD 134 | 134.0 | 85.0 |
