Air Core Drilling

What Is Air Core Drilling?

Air core drilling uses three-bladed steel or tungsten drill bits to bore holes into unconsolidated ground and is used when safe and clean removal of sample material is paramount.
Air Core Drilling is an inexpensive method of exploration drilling that can be employed when safe removal of sample material is paramount. Where possible, it is preferred over RAB (Percussion rotary air blast drilling) drilling and unlike the diamond drilling method, which withdraws a small diameter core of rock from the orebody, air core drilling is much faster and more cost-effective.

As the name suggests, air core drilling relies on compressed air to flush cutting samples out of your drill holes. This enables the safer collection of samples without unnecessary damage to the surrounding area and results in a more effective analysis sample.

How Does Air Core Drilling Work?

Air core drilling uses a three-bladed steel or tungsten drill bit to penetrate the weathered layer of loose soil and rock fragments. The drill rods are hollow and feature an inner tube with an outer barrel (similar to RC drilling).

Air core drilling works by using small compressors to drill holes into the weathered layer of loose soil and fragments of rock. After drilling is complete, an injection of compressed air is unleashed into the space between the inner tube and the drill rod’s inside wall, which flushes the cuttings up and out of the drill hole through the rod’s inner tube.

These samples then pass through a sample hose and into a cyclone, where they’re collected for review and assay.

Where is Air Core Drilling Applied?

Air core drilling is a valuable method of drilling for organisations looking to reduce the risk of sample cross-contamination. It’s commonly used in first-pass exploration drill programs on unconsolidated ground, with an optimal depth of up to 300 metres.

Advantages of Air Core Drilling

Air core drilling has clear advantages over other drilling methods.

  • It eliminates the need for casting holes.
  • It provides a more representative sample of material. The nature of the expulsion of the materials provides samples that are easier to analyse.
  • Delivers safer sample removal. Due to its reliance on compressed air injection, air core drilling involves less damage to the samples, when compared with blast drilling.
  • Boosts efficiencies and reduces costs. Air core drilling is an efficient method for removing material. It enables real-time sample collection, which speeds up drilling rates, resulting in reduced field costs. Air core drill rigs are also lighter in weight than other rigs, meaning they’re quicker and easier to transport.
  • Less chance of cross-contamination. As compressed air is used to flush the cuttings through the inner tube, there is less sample pollution than other methods.

Disadvantages of Air Core Drilling

While there are many advantages to air core drilling, it also comes with disadvantages when compared to other methods of drilling.

  • Air core drilling can be slower. While air core drilling is considered more efficient, the drills typically operate at a slower speed than other methods, making the drill process itself slower.
  • Depth limited. Depending on many variables but predominantly available air pressure, air core drilling is usually limited to depths of 50-120m.
  • Fresh rock penetration. While air core drilling can drill through cap rock at the top of a hole using a hammer or tri-cone roller, air core drilling is usually unable to penetrate fresh rock.

What’s The Difference Between Air Core Drilling and RC Drilling?

While the equipment used in air core drilling and RC drilling is similar, the mechanisms involved are different, so each is useful in different situations.

Both involve the use of compressed air to flush out samples. However, air core drilling is ideal where unconsolidated ground is present.

RC drilling on the other hand, uses the added element of concussive force to power the drill bit, pulverising the rock in its path. This makes RC drilling ideal for harder ground. RC drilling is also typically able to achieve greater depths, and better-quality samples, than other types of drilling.

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