Reverse Circulation use in drilling programs
Harley Hollier, Technical Director, Harlsan Industries
Summary: Considerations in setting up for a reverse circulation drilling program. The types of drilling programs and the issues surrounding equipment choices for drill rigs and support equipment.
Date: Feb 6, 2013
Key words: RC Drilling Consumables, Reverse Circulation Drilling, Drill String
Reverse Circulation is used in drilling programs for initial exploration and also for resource definition. There are two types of RC drilling. One is RC with hammer, used in medium and hard rock that can reach depths up to 800m. Rods are usually 4″ and 4 ½” diameters.
The other is Air Core drilling used in softer oxide and clay ground to depths of 100m using Air Core & Vacuum Bits designed specifically for the type of ground conditions. RC Rods used for Air Core drilling are normally 3’’ to 3 ½’’. Harlsan’s has broad experience in the design and manufacture of Air Core Drilling equipment to suit a variety of ground conditions.
Compared to diamond core drilling, RC drilling with inherently faster penetration rates provides several benefits:
- Direct drilling cost reductions in the range of 25% to 40%.
- Faster completion of drill programs with quicker delivery of results.
- Reduced man-hours at the drill with decreased exposure to potential accidents.
- Indirect cost reductions gained from a simplified sampling process.
- Requires less water than diamond drilling.
When setting up or buying a rig to commence exploration RC drilling there are a lot of factors to consider. Initial costs are high so you need to get it right the first time. Talking to peers in the industry plus rig and consumable manufacturers is a great way to get firsthand experience so that costly mistakes can be avoided. It would difficult to over emphasis the importance of paying careful attention to initial equipment purchases.
Choices like the type, configuration and setup of a rig has downstream affects on production rates, downtime, profitability and operator safety.
Exploration drilling requires support equipment. This can vary depending on the amount and depth of holes to be drilled as well as the remoteness of the location. Drilling companies will typically be set up with caravans, satellite communications, lighting towers, auxiliary compressors (with boosters) and support trucks carrying water, fuel, spare equipment & drilling consumables.
Site Grade Control
Reverse Circulation is the most commonly used drilling method for grade control in open pit mining operations. Grade control is used to define the ore grades and ore blocks in the pit and also provide knowledge for mine planning and blasting. This information is critical to reduce waste rock (dilution) in concentrator feed as dilution can vary from 5-40%. RC grade control is the most cost effective and accurate way to define boundaries between waste rock and ore bodies.