Particularly when it comes to exploration and grade control, there are a variety of factors to first consider when deciding which drilling method will suit your project best. Aside from time and cost, it is important to anticipate the environmental impact of the works, the benefits, the depth of drilling, sample quality, and any health and safety concerns.
What is Reverse Circulation Drilling?
As the best method for grade control, RC drilling is the method of which uses dual wall drill rods, consisting of both an outer drill rod, as well as an inner tube. These inner tubes are hollow, allowing for the drill cuttings to be transported back to the surface in a continuous, steady flow.
RC differs from other kinds of drilling (such as diamond or rotary air blast drilling) by gathering sample rock cuttings instead of rock core. The device that is commonly used is called a pneumatic reciprocating piston, which in essence acts like a hammer to drive a tungsten-steel drill bit into hard rock. This process occurs as follows:
- The hammer is used to remove rock samples which are pushed through the machine with compressed air.
- When air is blown down the annulus of the rod, the pressure shift creates a reverse circulation, bringing the cuttings up the inner tube. When the cuttings reach a deflector box at the top of the rig, the matter is moved through a hose attached to the top of the cyclone.
- The drill cuttings will travel around the cyclone until they fall through the bottom opening into a sample bag. These bags are marked with the location and depth of the place where the sample was collected and can be transported directly to the assay lab for analysis.
- The penetration rates of RC Drilling are comparable to open drilling methods, and are often faster at greater depths.
- When the cutting travels through the bit into the inner tube towards the cyclone, it is not introduced to other areas of the hole, keeping it free of cross-contamination. This creates the possibility of producing large quantities of high quality, reliable samples.
- RC Drilling is versatile in extreme conditions, making it ideal in arid, dessert landscapes across Australia.
- This type of drilling is also more cost-effective than diamond drilling, with operating costs reduced by up to 40%.
Why is RC drilling best for grade control?
Grade control is used to define the ore grades and blocks in the pit. For an exploration program, the quality of the samples is imperative for mine planning and blasting, as the samples must be reliably accurate.
RC drilling is the ideal method for grade control in open pit mining operations, for a variety of reasons, including:
- samples obtained by way RC drilling are free of contaminants,
- the samples are collected at the drill and sent directly to the lab to be assessed
- RC sampling requires less handling than other methods
- less handling results in cost reduction and faster turnaround times
The reliability of the cuttings produced during RC drilling is an industry asset, RC grade control is the most cost effective and efficient way to differentiate between waste rock and minerals.
Due to RC drilling leaving behind a small rig footprint, it eliminates the need for extensive earthworks. This means RC drilling has a minimal environmental impact. This kind of exploration drilling is also strictly controlled and regulated when an exploration license is approved. Most drilling requires further governmental approval, which will demand a thorough environmental survey, proposed methodology, administrative plan, and environmental mitigation.
While different locations, companies and worksites might have varying safety regulations, there are of course general precautions to observe, such as always wearing some type of personal protection, from earmuffs to safety footwear, respiratory masks, hard hats, and industrial gloves.
Rig operators must also remain vigilant about a number of hazards including:
- the physical strain they could receive from manually handling samples,
- the potential of falling objects,
- proximity to compressed air, and
- pinch points or areas around the rig that could be the source of crush injuries.