The Difference Between Aircore, RC and Diamond Drilling

  Educational Article

PUBLISHED: 21-02-2022 11:39 a.m.

3 minute read

Drilling underpins the activities of junior exploration companies.

Drilling is the only surefire way to find out what mineralisation lies below the surface - and if you invest in mining explorers, expect to encounter a lot of drilling.

Discovering and defining a deposit is like putting together a complicated puzzle. The more drilling a company does, the clearer the picture for investors.

There are a few different types of drilling that you will encounter on your investment journey and each plays a different role in solving the exploration puzzle.

Drilling programs will often occur in chunks of metres to drill, so 3000m of drilling or 10,000m of drilling, for a specific period of time.

Once the drilling is complete, investors and the company will evaluate the results to better inform the next drilling program.

The three types of drilling that we will look at today are:

  • Aircore Drilling (AC Drilling)
  • Reverse Circulation Drilling (RC Drilling)
  • Diamond Drilling

As an investor it's important to understand each of the different types of drilling and how they help to solve the ‘puzzle’ of discovering and defining a deposit.

What is Aircore (AC) Drilling?

AC drilling is one of the cheapest types of drilling that an exploration company can do.

AC drilling is used in first pass exploration programs and used as a precursor to generating higher priority drill targets.

The benefits of AC drilling is that it uses a small rig, which can drill quicker and at a much cheaper cost.

AC drilling is however limited by the depths at which it can reach, ~150m at best, and the type of rock structures it can penetrate.

As a result, very rarely are discoveries made during AC drilling programs.

Almost always AC drilling is used as a ranking exercise to try and narrow down a large sample of targets into ‘high priority targets’ which can then be drilled using heavier, more expensive rigs.

What is Reverse Circulation (RC) Drilling?

RC drilling is the most common type of drilling an exploration company will choose to do.

RC drilling is popular amongst exploration companies mostly because these drill-rigs are heavy and powerful enough to drill down to depths of upto 600m (depending on the rock formations being targeted).

Most economic deposits start showing some mineralisation before 600m in depth, as a result explorers tend to prefer RC drilling programs so as not to lower the probabilities of missing anything.

RC drilling also produces higher quality samples, again increasing the number of results that come from a drilling program.

The downside to RC drilling is that it is relatively expensive versus an AC program, this usually means that RC drilling is only done on higher priority targets where the exploration companies are confident they can make a large-scale discovery.

What is Diamond Drilling?

Diamond drilling is the next step up from RC drilling, with the primary difference being that the drill bit on the end of the rig is diamond encrusted.

Diamonds are known to be one of the hardest materials in the world, making them perfect to put on the end of a drilling rig and penetrate through hard rock formations. As a result diamond drilling is often used when looking to drill down to really high depths.

Another reason diamond drilling is used is because it produces clean core-logs.

With AC or RC drilling the core sample can crumble, rendering it unusable by the assay lab to generate an accurate assessment of the mineralisation.

The clean cuts produced by diamond drilling provide a much higher sample recovery rate, and are more representative of the ore body being targeted.

Diamond drilling provides the best reflection of what is under the surface, however it is the most expensive type of drilling.

Explorers under normal circumstances will deploy diamond drill rigs either when they have found a mineralised system and want to further define it or if they are drilling into hard rock structures at depth.