Core orientation is a method of measuring the orientation of the length of rock that is cored when drilling.
Usually core orientation is achieved by fitting a device or instrument above the core barrel (some may fit within it) that records its own rotational angle (relative to vertical) when the core is broken off by the driller. When the rock core is recovered the recorded angle in the tool is used to orientate the core into the position it was.
This information, together with borehole survey information, provides an accurate orientation of the core. This in turn allows the correct location of any and all linear features in the rock and so allows accurate modeling of the rock structures, lithological features and/or mineral deposit.
A single instrument involves running the instrument with the core barrel, recording the angle, breaking core, retrieving the core barrel and instrument then orientating the core at surface before restarting/attaching the tool to a core barrel to repeat the process. This involves a delay (minutes) in drilling whilst the orientation is made at surface. In some projects this time may not be important but, in others, this delay may add up to be an important consideration when many core runs are being made. Mistakes may be made when a Driller measuring the core orientation feels under time pressure to get the reading.