Reverse circulation (R.C.) drilling or the dual tube method as it is quite commonly known, has a unique place in conventional mineral drilling. It can be classified half-way between open hole drilling at the lower end of the scale and diamond drilling at the upper end. The system basically consists of two tubes, one inside the other, with compressed air flowing between the inner and outer tubes. Sample cuttings return up the inner tube through the head of the rig and via a hose to a cyclone where the sample is collected._x000D_
This system means that the cuttings are free of contamination as they are at no time in contact with the outside formation of the hole._x000D_
Reverse circulation drilling is divided into two areas: R.C. Roller and Blade for softer formations; and R.C._x000D_
Percussion for harder formations.