Underground Core Drilling

HOW IT WORKS?

Diamond drilling gives a good indication of vein location and structure, but it is not an effective measure of grade. For a better understanding of grade and geological continuity of the vein, the underground development became a key method. The main challenge of the underground exploration drilling is to gather ground samples deeper in the ground in small spaces within areas such as tunnels and mines.

Application Used for very accurate underground solid sampling extracted from deep, hard rock environments for stratigraphy and mineral content analysis
Sample quality High core sample with very reliable results
Drilling speed Slow speed depending on ground conditions normally 25 – 30m per shift
Hole depth The hole’s depth depends on the capabilities of the drilling rig, but typically 300 m
Hole size 46 to 146 mm
Flexibility Taking into account the ground geological characteristics and choosing accordingly the right range of tools, allow to be very flexible with this method of drilling
Cost High, because of drilling speed limitations and expensive tailor made drilling consumables made to suit the rig.
Time Time consuming as drilling is done slowly to preserve the life of the parts and also because of the rock hardness
Technique A drill is required to produce the rotation and force needed to drive a string of tools consisting of a bit  which rotates at high speed, cutting through the fresh rock, core barrel assembly, drill rods through the ground, all the while retrieving a solid core sample. Water is also used for lubrication, cooling, and removal of drill cuttings from the hole.
Challenges The main challenge related to underground core drilling is providing a large inner diameter through the drill pipe to allow easy retrieval of core barrels and surely, the drilling operations in a limited space
Products & Solutions

Drill Structure

Diamond core drilling is so called because it uses a ‘diamond bit’. This drill bit is composed of group of small, industrial grade diamonds set into a metallic, soft matrix. As the ground is drilled, this matrix will wear away and expose more diamonds.
This is then attached to a drill rod, which is around 10 foot in length, and then more sections of pipe can be attached to the top of this so a greater depth can be drilled. The depth that is drilled to is estimated by the number of rods attached to the top of the drill rod.

 

Inside the drill rod, a core tube is attached to a cable via a latching mechanism. The core tube is lifted to the surface using the cable, so the solid core can be removed.

There are two primary types of diamond drilling-rotary drilling and wireline drilling. Rotary drilling is used primarily for bore hole drilling, whereas wireline drilling is used for solid core sampling.

There a five standard tube sizes associated with wire line drilling as follows:

  • AQ (Hole diameter: 48mm)
  • BQ (60mm)
  • NQ (75.5mm)
  • HQ (96mm)
  • PQ (122.6mm)

The drill size used depends on the desired core diameter and the desired depth of drilling, and the wider the diameter of the tube, the more power that is required to drive the drilling.