Reverse Circulation drilling, or RC drilling, uses dual wall drill rods consisting of an outer drill rod with an inner tube. These hollow inner tubes allow the drill cuttings to return back to the surface in a continuous, steady flow.
The advantage of this drilling technique is that it produces large quantities of high quality, reliable samples free of cross-contamination. The cuttings also allow surveyors to locate mineral deposits more precisely as the samples are identified by the exact depth and location that they were found.
Reverse circulation drilling produces dry rock chips, large air compressors dry the rock ahead of the advancing drill bit. It is slower, but achieves better penetration than other types of drilling.