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Diamond drill core laid out in a core box CC-BY-SA

Diamond Drill Core Logging

A qualified and skilled geologist normally carries out core logging.
This is done to extract as much information out of the core as possible.
Drill-core comes in various sizes including; PQ which is 85.0 mm in
diameter, HQ is 63.5 mm and NQ is 47.6 mm. typically as the holes gets
deeper the drill core size is reduced.
After collecting the core trays from the drill rig they are laid out in an
area where logging, sampling and storage takes place, normally a
purpose built core shed. First, the core trays are laid out in order on trestle tables. Core is washed down
with water and a brush is used to remove any mud and other residue from the core’s surface.
The core is then marked up; with the start and end of each meter interval is marked on the core with a
brightly coloured wax pencil. During marking up any gaps in the drilling are noted and a wooden block is
placed at the location of the missing core. Core can be lost down the hole when drilling encounters faults
and fault zones. Rock within these zones is often broken up and may fall out of the drill pipe when it is
being removed from the hole. Gaps in the core can be significant.

Diamond Core Sampling

Core sampling involves identifying the mineralised zones that require assaying. The procedure is similar
to that used for rock and soil sampling. The core several metres either side of the identified zone is also
sampled to establish if the adjacent wall rock are mineralised too. The technician then uses a rock saw,
, to cut each metre of core in half along its length. One half is put into a plastic sample bag and the other
half is retained and kept in the core tray for later reference. A duplicate sample is obtained by cutting the
halved core again resulting in a quartered piece of core. One of the quartered pieces is submitted as the
sample and the other is submitted as the duplicate.

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