Abstract
In diamond drilling, an annular, diamond impregnated cutting tool (called a bit) mounted on the end of a rotating string of hollow steel rods, cuts a solid cylinder of rock (core) which passes up inside the drill rods as the bit advances (Fig. 5.3). The bit is lubricated with water (or sometimes a special water/mud mixture) which is pumped to the cutting face down the inside of the rods, before returning to the surface between the rods and the sides of the hole. At surface, the return water is usually collected in a sump where fine suspended ground rock material can settle. The water can then be recirculated to the drill bit.
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Notes
- 1.
The commonly used standard core diameters for wireline drilling are AQ, 27 mm; BQ 36.5 mm; NQ 47.6 mm; HQ, 63.5 mm and PQ, 85 mm.
- 2.
The system described here is called wire-line drilling and was invented by the US Lo ngyear Company in 1958. By the late 1960s it was in almost universal use. Before wireline drilling, the whole string of rods had to be pulled from the ground in order to recover core from each advance of the drill.
- 3.
Although it may be necessary to include the sign when inputting hole survey data to some computer programs.
- 4.
The position in three dimensions of surface features should be determined to a comparable accuracy to the location of features in the drill core. Even where there is no surface outcrop, the surface profile of the section often reflects the influence of underlying geology and can provide valuable extra clues when it comes to interpreting the drill section.
- 5.
As W.C. Peters (1987) says in his book Exploration and Mining Geology: “Logging is… most quickly done for the main objective of the moment. The main objective of the moment is to find or to outline an orebody, not to log core.”
- 6.
Roy Woodall, former Exploration Director for Western Mining Corporation, was quoted (1995) as saying: “We’ve relogged the drill core from the Kambalda area (West Australian Ni/Au Camp) three times and each time we do it, we find a new orebody.”
- 7.
But only if the core is oriented.
- 8.
The same technique is useful for detecting cryptic minerals present in any hand specimen.
- 9.
He also had the mineral pumpellyite named after him.
- 10.
- 11.
An a ntiform is any upwards-closing folded surface. A synform is any downwards-closing folded surface. The terms anticline and syncline can strictly only be used when describing sedimentary sequences where the original stratigraphic top of the sequence is known. Thus in an anticline beds become older towards the centre of the fold. In a syncline, beds become older away from the centre of the fold.
- 12.
This is a good illustration of the aphorism – “The Medium is the Message” – coined by Marshall McCluhan (1964).
- 13.
This type of logging has been referred to as fixed-format logging using alpha-numeric codes. The term used here is considered to better reflect the methodology behind this system.
- 14.
Between 1995 and 1997, at the Busang gold prospect in Indonesia, some employees of the Canadian junior exploration company Bre-X carried out one of the most massive frauds in mining history. On an almost industrial scale, entire drill core was crushed, salted with extra gold, before being sent for assay. The Bre-X stock price soared from a few cents to over $285. The lack of retained core to compare with the fraudulent assays meant that the few honest explorationists who made it to the remote jungle site were unable to recognise the deception (see Gould and Willis, 1997; Hutchison, 1998).
- 15.
RQD or Rock Quality Designation is defined as percentage core recovered during drilling, counting only those pieces of intact rock over 100 mm long.
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Marjoribanks, R. (2010). Diamond Drilling. In: Geological Methods in Mineral Exploration and Mining. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-74375-0_7
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