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7. ROCK CORING
1. The acceptable minimum core diameter shall be 52mm (NMLC triple tube core
barrels). However, when directed by the S.O., cores of larger diameter shall be
used.
2. Core drilling in rock shall be limited to a maximum length of 1.5m. When less than
95% of the core is recovered from a run, the length of the following run shall be
reduced by 50% unless otherwise directed by the S.O. If less than 50% recovery is
achieved, the following run shall not exceed 0.5m until full recovery is achieved
from two consecutive runs until minimum coring length as specified is achieved.
3. Core Recovery Ratio (CRR) and Rock Quality Designation (RQD)
a. CRR – The ratio of the total length of the good quality cores over the drilling, expressed to
the nearest 5%.
b. RQD – The ratio of the length of good quality cores each exceeding 100mm in length over
the drilling run, correct to be nearest 5%.
